Home > Products > State Listing > Illinois Data
Latest:
 AFDLOT |  AFDILX |
  [top]

000
FXUS63 KLOT 010016
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
616 PM CST SAT JAN 31 2015

.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...
312 PM CST

MONDAY NIGHT THROUGH SATURDAY...

THE START OF THE FORECAST PERIOD WILL BE MARKED WITH EXITING
SNOWFALL WITH THE DEPARTING WINTER STORM...WHILE LAKE EFFECT SNOW
SHOWERS PERSIST NEAR THE LAKE ON MONDAY. WITH THE DEPARTING UPPER
LEVEL TROUGH AND ASSOCIATED SURFACE LOW...LOW LEVEL FLOW WILL
CONTINUE TO BACK MORE TO THE NORTH AND NORTHWEST. HOWEVER...THE
EXTENT OF THIS VEERING THROUGHOUT THE DAY WILL DETERMINE THE
PLACEMENT/DURATION OF THESE LINGERING SNOW SHOWERS WITH SOME
GUIDANCE KEEPING THE POSSIBILITY FOR LAKE EFFECT SNOW SHOWERS INTO
ILLINOIS DURING THIS TIME. EVEN IF THIS WERE TO OCCUR...NOT OVERLY
CONCERNED WITH TOO MUCH ADDITIONAL SNOWFALL DURING THIS TIME WITH
DEPARTING SYNOPTIC LIFT AND MODEST INVERSION HEIGHTS. SHIFTING HIGH
PRESSURE ACROSS THE REGION WILL ALLOW FLOW TO CONTINUE BACKING AND
ANY LINGERING SNOW SHOWERS TO PUSH FURTHER EAST LATER IN THE DAY AND
INTO MONDAY EVENING. APPROACHING SPEED MAX MONDAY NIGHT WILL HELP
STEER ANOTHER AREA OF LIGHT SNOW TOWARDS THE CWA AND DO THINK IT
WILL REACH NORTHERN ILLINOIS...BUT IT SHOULD BE DIMINISHING WITH
DISJOINTING LARGE SCALE SUPPORT AND WITH LITTLE ACCUMULATION
EXPECTED. TEMPS IN THE SINGLE DIGITS ARE LIKELY MONDAY NIGHT...WITH
INCREASING CLOUD COVER AND WHILE THE SURFACE RIDGE QUICKLY SHIFTS TO
THE SOUTHEAST.

ACTIVE WEATHER PATTERN WILL PERSIST THROUGH MID WEEK AS NORTHWEST
FLOW USHERS IN AN ADDITIONAL MID/UPPER LEVEL SYSTEM. THIS APPEARS TO
BE MORE OF A VIGOROUS SYSTEM WITH ACCUMULATING SNOW APPEARING TO BE
A POSSIBILITY LATE TUESDAY AND TUESDAY NIGHT. PRECIP SHOULD EXIT
WEDNESDAY MORNING...AS LARGE UPPER LEVEL TROUGH DIGS SOUTH ACROSS
THE REGION. STRONG PUSH OF COLDER AIR WILL OCCUR AND HELP WITH
ADDITIONAL LAKE EFFECT SNOW SHOWERS ON WEDNESDAY AS WELL AS MUCH
COLDER LOW TEMPS...WITH BELOW ZERO TEMPS APPEARING LIKELY WEDNESDAY
NIGHT AND THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* PRECIPITATION MOVING IN 02-04Z MAY START AS A PERIOD OF RAIN AND
  SLEET BUT QUICKLY TURN TO SNOW. SNOW COVERAGE AND INTENSITY
  VARIES THROUGH EARLY TONIGHT BECOMING MORE WIDESPREAD AND
  INTENSE OVERNIGHT AND CONTINUES THROUGH SUNDAY.

* INTERMITTENT IFR VSBY IN SNOW THIS EVENING WITH STEADIER IFR
  VSBY LATER TONIGHT. 1/2-3/4SM VSBY LIKELY FROM EARLY SUNDAY
  MORNING THROUGH THE AFTERNOON AND POSSIBLY THE EVENING. PERIODIC
  1/4SM VSBY POSSIBLE...ESPECIALLY DURING THE AFTERNOON.

* VARIABLE WINDS TURN NORTHEAST THIS EVENING THEN GRADUALLY
  INCREASE IN SPEED LATE TONIGHT...THEN RAMP UP LATE SUNDAY
  MORNING. 30-35 KT GUSTS LIKELY SUNDAY AFTERNOON.

* SNOW MAY TAKE UNTIL LATE SUNDAY EVENING OR EARLY SUNDAY NIGHT TO
  END. IFR VSBY MAY CONTINUE THROUGH THIS TIME.

MDB

//DISCUSSION...UPDATED 00Z...

TONIGHT...MAJOR WINTER STORM IS GETTING UNDERWAY THIS EVENING AS
LOW PRESSURE DEVELOPS ACROSS THE CENTRAL/SOUTHERN HIGH PLAINS.
PRECIPITATION IS STEADILY MOVING INTO THE AREA FROM THE SOUTHWEST
AND HAS MAINLY BEEN RAIN THUS FAR BUT AM NOW STARTING TO SEE SOME
REPORTS OF WET SNOW. A COLD FRONT IS SLOWLY SAGGING SOUTHWARD INTO
FAR NORTHERN ILLINOIS WHICH IS ALLOWING COOLER AND DRIER AIR TO
MOVE IN. THIS WILL LIKELY ALLOW PRECIPITATION TO MORE QUICKLY
TRANSITION TO SNOW AT THE TERMINALS AFTER BEGINNING AS A RAIN/SNOW
MIX WITH SOME SLEET ALSO POSSIBLE. COVERAGE AND INTENSITY OF SNOW
WILL LIKELY BE VARIABLE INTO THE EARLY OVERNIGHT BEFORE BECOME
MORE WIDESPREAD AND INTENSE LATE TONIGHT. THIS WILL LIKELY LEAD TO
VARIABILITY IN VSBY AND MAY BE A LITTLE TOO PESSIMISTIC WITH
PREVAILING 1-2SM VSBY...BUT CONFIDENCE 1-2SM VSBY WILL AT LEAST
OCCUR AT TIMES THIS EVENING. SUB 1SM VSBY IS LIKELY BY LATE
TONIGHT. ACCUMULATION RATES OF UP TO AROUND A HALF INCH PER HOUR
ARE EXPECTED OVERNIGHT.

SUNDAY AND SUNDAY EVENING...THE PEAK SNOW INTENSITY IS EXPECTED
DURING THE DAY SUNDAY. WIDESPREAD SNOW WILL PERSIST ACROSS THE
TERMINALS WITH 1/2-3/4SM VSBY EXPECTED FOR MOST OF THE DAY. 1/4SM
VSBY WILL LIKELY OCCUR AT TIMES...ESPECIALLY DURING THE AFTERNOON
AS WINDS PICK UP CAUSING BLOWING SNOW AS SNOW TYPE BECOMES
DRIER/FLUFFIER. NORTHEAST WINDS WILL STEADILY RAMP UP LATE SUNDAY
MORNING AND PEAK DURING THE AFTERNOON WITH 30-35 KT GUSTS LIKELY.
AM CONCERNED THAT GYY MAY SEE GUSTS CLOSE TO 40 KT GIVEN PROXIMITY
TO THE LAKE. ACCUMULATION RATES OF 0.5-0.75 IN/HR ARE LIKELY WITH
SOME 1 IN/HR RATES POSSIBLE AT TIMES. LAKE ENHANCEMENT MAY OCCUR
LATER IN THE AFTERNOON AND MORESO DURING THE EVENING SO SUB 1SM
VSBY MAY CONTINUE THROUGH THE EVENING...WITH 1/2SM VSBY CERTAINLY
POSSIBLE AS LONG AS SNOW IS FALLING AND THE WINDS CONTINUE. THE
END TIME OF SNOW AND IMPROVEMENT OF VSBY IS NOT CERTAIN AT THIS
TIME...THOUGH RFD SHOULD SEE IMPROVING CONDITIONS DURING THE
EVENING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE PRECIP ARRIVAL TIMING. MEDIUM-HIGH CONFIDENCE IN
  RAIN/MIX OCCURRING INITIALLY. MEDIUM-HIGH CONFIDENCE IN
  INTERMITTENT CHANGES IN INTENSITY THROUGH EARLY TONIGHT BEFORE
  STEADILY INCREASING LATE.

* MEDIUM-HIGH CONFIDENCE IN IFR OCCURRING THIS EVENING...BUT LOW-
  MEDIUM CONFIDENCE IN STEADY DURATION. HIGH CONFIDENCE IN STEADY
  IFR LATE TONIGHT. HIGH CONFIDENCE IN MAINLY 1/2-3/4SM VSBY
  SUNDAY. MEDIUM CONFIDENCE IN PERIODIC 1/4SM VSBY...ESPECIALLY
  SUNDAY AFTERNOON.

* HIGH CONFIDENCE IN WIND TRENDS INCLUDING 30-35 KT GUSTS SUNDAY
  AFTERNOON.

* LOW CONFIDENCE IN END TIME OF SNOW BUT HIGH CONFIDENCE IN IT
  CONTINUING THROUGH SUNDAY AFTERNOON.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY...IFR VSBY
POSSIBLE.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

MDB

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 010016
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
616 PM CST SAT JAN 31 2015

.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...
312 PM CST

MONDAY NIGHT THROUGH SATURDAY...

THE START OF THE FORECAST PERIOD WILL BE MARKED WITH EXITING
SNOWFALL WITH THE DEPARTING WINTER STORM...WHILE LAKE EFFECT SNOW
SHOWERS PERSIST NEAR THE LAKE ON MONDAY. WITH THE DEPARTING UPPER
LEVEL TROUGH AND ASSOCIATED SURFACE LOW...LOW LEVEL FLOW WILL
CONTINUE TO BACK MORE TO THE NORTH AND NORTHWEST. HOWEVER...THE
EXTENT OF THIS VEERING THROUGHOUT THE DAY WILL DETERMINE THE
PLACEMENT/DURATION OF THESE LINGERING SNOW SHOWERS WITH SOME
GUIDANCE KEEPING THE POSSIBILITY FOR LAKE EFFECT SNOW SHOWERS INTO
ILLINOIS DURING THIS TIME. EVEN IF THIS WERE TO OCCUR...NOT OVERLY
CONCERNED WITH TOO MUCH ADDITIONAL SNOWFALL DURING THIS TIME WITH
DEPARTING SYNOPTIC LIFT AND MODEST INVERSION HEIGHTS. SHIFTING HIGH
PRESSURE ACROSS THE REGION WILL ALLOW FLOW TO CONTINUE BACKING AND
ANY LINGERING SNOW SHOWERS TO PUSH FURTHER EAST LATER IN THE DAY AND
INTO MONDAY EVENING. APPROACHING SPEED MAX MONDAY NIGHT WILL HELP
STEER ANOTHER AREA OF LIGHT SNOW TOWARDS THE CWA AND DO THINK IT
WILL REACH NORTHERN ILLINOIS...BUT IT SHOULD BE DIMINISHING WITH
DISJOINTING LARGE SCALE SUPPORT AND WITH LITTLE ACCUMULATION
EXPECTED. TEMPS IN THE SINGLE DIGITS ARE LIKELY MONDAY NIGHT...WITH
INCREASING CLOUD COVER AND WHILE THE SURFACE RIDGE QUICKLY SHIFTS TO
THE SOUTHEAST.

ACTIVE WEATHER PATTERN WILL PERSIST THROUGH MID WEEK AS NORTHWEST
FLOW USHERS IN AN ADDITIONAL MID/UPPER LEVEL SYSTEM. THIS APPEARS TO
BE MORE OF A VIGOROUS SYSTEM WITH ACCUMULATING SNOW APPEARING TO BE
A POSSIBILITY LATE TUESDAY AND TUESDAY NIGHT. PRECIP SHOULD EXIT
WEDNESDAY MORNING...AS LARGE UPPER LEVEL TROUGH DIGS SOUTH ACROSS
THE REGION. STRONG PUSH OF COLDER AIR WILL OCCUR AND HELP WITH
ADDITIONAL LAKE EFFECT SNOW SHOWERS ON WEDNESDAY AS WELL AS MUCH
COLDER LOW TEMPS...WITH BELOW ZERO TEMPS APPEARING LIKELY WEDNESDAY
NIGHT AND THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* PRECIPITATION MOVING IN 02-04Z MAY START AS A PERIOD OF RAIN AND
  SLEET BUT QUICKLY TURN TO SNOW. SNOW COVERAGE AND INTENSITY
  VARIES THROUGH EARLY TONIGHT BECOMING MORE WIDESPREAD AND
  INTENSE OVERNIGHT AND CONTINUES THROUGH SUNDAY.

* INTERMITTENT IFR VSBY IN SNOW THIS EVENING WITH STEADIER IFR
  VSBY LATER TONIGHT. 1/2-3/4SM VSBY LIKELY FROM EARLY SUNDAY
  MORNING THROUGH THE AFTERNOON AND POSSIBLY THE EVENING. PERIODIC
  1/4SM VSBY POSSIBLE...ESPECIALLY DURING THE AFTERNOON.

* VARIABLE WINDS TURN NORTHEAST THIS EVENING THEN GRADUALLY
  INCREASE IN SPEED LATE TONIGHT...THEN RAMP UP LATE SUNDAY
  MORNING. 30-35 KT GUSTS LIKELY SUNDAY AFTERNOON.

* SNOW MAY TAKE UNTIL LATE SUNDAY EVENING OR EARLY SUNDAY NIGHT TO
  END. IFR VSBY MAY CONTINUE THROUGH THIS TIME.

MDB

//DISCUSSION...UPDATED 00Z...

TONIGHT...MAJOR WINTER STORM IS GETTING UNDERWAY THIS EVENING AS
LOW PRESSURE DEVELOPS ACROSS THE CENTRAL/SOUTHERN HIGH PLAINS.
PRECIPITATION IS STEADILY MOVING INTO THE AREA FROM THE SOUTHWEST
AND HAS MAINLY BEEN RAIN THUS FAR BUT AM NOW STARTING TO SEE SOME
REPORTS OF WET SNOW. A COLD FRONT IS SLOWLY SAGGING SOUTHWARD INTO
FAR NORTHERN ILLINOIS WHICH IS ALLOWING COOLER AND DRIER AIR TO
MOVE IN. THIS WILL LIKELY ALLOW PRECIPITATION TO MORE QUICKLY
TRANSITION TO SNOW AT THE TERMINALS AFTER BEGINNING AS A RAIN/SNOW
MIX WITH SOME SLEET ALSO POSSIBLE. COVERAGE AND INTENSITY OF SNOW
WILL LIKELY BE VARIABLE INTO THE EARLY OVERNIGHT BEFORE BECOME
MORE WIDESPREAD AND INTENSE LATE TONIGHT. THIS WILL LIKELY LEAD TO
VARIABILITY IN VSBY AND MAY BE A LITTLE TOO PESSIMISTIC WITH
PREVAILING 1-2SM VSBY...BUT CONFIDENCE 1-2SM VSBY WILL AT LEAST
OCCUR AT TIMES THIS EVENING. SUB 1SM VSBY IS LIKELY BY LATE
TONIGHT. ACCUMULATION RATES OF UP TO AROUND A HALF INCH PER HOUR
ARE EXPECTED OVERNIGHT.

SUNDAY AND SUNDAY EVENING...THE PEAK SNOW INTENSITY IS EXPECTED
DURING THE DAY SUNDAY. WIDESPREAD SNOW WILL PERSIST ACROSS THE
TERMINALS WITH 1/2-3/4SM VSBY EXPECTED FOR MOST OF THE DAY. 1/4SM
VSBY WILL LIKELY OCCUR AT TIMES...ESPECIALLY DURING THE AFTERNOON
AS WINDS PICK UP CAUSING BLOWING SNOW AS SNOW TYPE BECOMES
DRIER/FLUFFIER. NORTHEAST WINDS WILL STEADILY RAMP UP LATE SUNDAY
MORNING AND PEAK DURING THE AFTERNOON WITH 30-35 KT GUSTS LIKELY.
AM CONCERNED THAT GYY MAY SEE GUSTS CLOSE TO 40 KT GIVEN PROXIMITY
TO THE LAKE. ACCUMULATION RATES OF 0.5-0.75 IN/HR ARE LIKELY WITH
SOME 1 IN/HR RATES POSSIBLE AT TIMES. LAKE ENHANCEMENT MAY OCCUR
LATER IN THE AFTERNOON AND MORESO DURING THE EVENING SO SUB 1SM
VSBY MAY CONTINUE THROUGH THE EVENING...WITH 1/2SM VSBY CERTAINLY
POSSIBLE AS LONG AS SNOW IS FALLING AND THE WINDS CONTINUE. THE
END TIME OF SNOW AND IMPROVEMENT OF VSBY IS NOT CERTAIN AT THIS
TIME...THOUGH RFD SHOULD SEE IMPROVING CONDITIONS DURING THE
EVENING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE PRECIP ARRIVAL TIMING. MEDIUM-HIGH CONFIDENCE IN
  RAIN/MIX OCCURRING INITIALLY. MEDIUM-HIGH CONFIDENCE IN
  INTERMITTENT CHANGES IN INTENSITY THROUGH EARLY TONIGHT BEFORE
  STEADILY INCREASING LATE.

* MEDIUM-HIGH CONFIDENCE IN IFR OCCURRING THIS EVENING...BUT LOW-
  MEDIUM CONFIDENCE IN STEADY DURATION. HIGH CONFIDENCE IN STEADY
  IFR LATE TONIGHT. HIGH CONFIDENCE IN MAINLY 1/2-3/4SM VSBY
  SUNDAY. MEDIUM CONFIDENCE IN PERIODIC 1/4SM VSBY...ESPECIALLY
  SUNDAY AFTERNOON.

* HIGH CONFIDENCE IN WIND TRENDS INCLUDING 30-35 KT GUSTS SUNDAY
  AFTERNOON.

* LOW CONFIDENCE IN END TIME OF SNOW BUT HIGH CONFIDENCE IN IT
  CONTINUING THROUGH SUNDAY AFTERNOON.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY...IFR VSBY
POSSIBLE.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

MDB

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





  [top]

000
FXUS63 KILX 312346
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
546 PM CST Sat Jan 31 2015

.SHORT TERM...(Tonight)
ISSUED AT 304 PM CST SAT JAN 31 2015

Latest surface map shows the low pressure with our storm system
organizing across Colorado early this afternoon, with a frontal
boundary arcing northeast along the Iowa/Minnesota border to just
north of Lake Huron. Upper wave is digging across the
Montana/Wyoming Rockies, as an upper low continues to spin just
south of Arizona. Leading edge of the precipitation shield with this
storm system has edged into the forecast area this afternoon. Some
sprinkles reported as far east as Clinton, but precipitation remains
light as there is a fair amount of dry air at the surface to
overcome. Radar mosaics showing the more organized rain back in
central Missouri and Iowa.

Forecast remains a challenge for tonight. Most of the current
guidance is suggesting precipitation being all rain much of the
evening, with a transition toward snow occurring across the northern
CWA late evening. Complicating matters is the indication by most of
the models that there will likely be a period of dry conditions
across the south half of the forecast area this evening, before
strong isentropic lift moves in from Missouri after midnight and
rapidly moistens the lower atmosphere again. The GFS came in on the
warmer end of the guidance with mainly rain into Sunday morning as
far north as I-72, while the remaining guidance rapidly cools the
column as the precipitation begins, with a switchover to snow. Have
kept a mix in the grids along I-72 past midnight before
transitioning to snow there between midnight and 3 am, with the
southeast CWA remaining mainly rain. Amount-wise, think that 3 to 5
inches of snow is likely north of a Havana to Bloomington line
tonight, with 1-2 inches along I-72, although this area remains
concerning due to the potential mixture lasting longer. Also
complicating things is temperatures above freezing in many areas,
which could limit some of the accumulations unless the snow is
falling heavy enough.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 304 PM CST SAT JAN 31 2015

Main focus for this forecast period continues to be the winter
weather system that will be moving across the area Sunday through
Sunday night. Over most of the area, precip should have changed over
to all snow, mainly along and north of Quincy to Paris line. Just
south of this line, precip will still be a mix of rain and snow, and
then south of I-70 it should be all rain. As the low pressure area
tracks across southern IL during the afternoon, colder air will
advect into the area and the southeast counties will change to a mix
of rain and snow, while areas north of I-70 will be all snow. Models
seem to be in fairly good agreement with the track of the system,
but differ on the temp profile during the morning hours, especially
for areas surrounding the I-72 to Danville corridor. NAM is cooler,
while the GFS is warmer and would mean more rain than snow. This
continues to be the tricky part of the forecast since the temp
profile plays into the amount of snow/snow accumulation those areas
will have. Looking at current snowfall grids, appears that Piatt,
Champaign, and Vermilion counties could reach warning criteria
snowfall Sunday, so will be adding them into the current winter
storm warning. This coincides with the eastward movement of the low
pressure area and lines up well with Indy. Counties just to the
south of this area will still remain in an advisory as the mix of
rain and snow will likely keep snowfall totals below 6 inches. Then
the 500mb trough will move across the area Sunday evening and then
bring an end to the snow by midnight.

The system will also be deepening some as it moves across the area,
and with colder air advecting into the system, the gradient will
become tighter, which means that the winds will increase and become
gusty for Sunday afternoon through Sunday night. Therefore, there
could be areas of blowing and drifting snow in the north Sunday
afternoon and then along and north of Quincy to Paris line for
Sunday evening. As the winds decrease overnight, the blowing snow
will become patchy. The areas of blowing and drifting snow will be
where most of the snow will have fallen. Believe the blowing and
drifting will be possible, even though the initial snowfall might be
heavier due to the amount of moisture. The snowfall during Sunday
afternoon and evening should be lighter given that the water content
should be drier than the earlier snowfall. Wind gusts should reach
between 30 and 35 mph during the afternoon and into the evening.

After this system, dry and cold weather is expected for Monday.
However, a clipper system is forecast to drop into the area and
bring a little bit of more snow to northern parts of the CWA for Mon
night through Tue night. Any snowfall looks to be less than one half
inch since moisture for this system will be very limited. Beyond
this, conditions will be dry through the rest of the week.

Temps will still be on the warm side Sunday, but then become much
colder for Sun night as colder air advects into the area behind the
system. Temps will remain cold for Monday and Mon night behind the
system but then warm slightly for Tue as the clipper system moves
through the area. Once the clipper moves through, colder air will
return for Wed night through Friday. Overnight low Wed night and
Thur night will be in the single digits for the northern half of the
CWA with some sites likely getting below zero. Temps will then begin
to warm again for the beginning of the weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 545 PM CST SAT JAN 31 2015

Initial band of precipitation associated with the approaching
winter storm is currently lifting through the area late this
afternoon. Most of the precip has been in the form of light rain:
however, some higher reflectivity echoes seen on radar lifting
northward across the I-74 corridor have resulted in a brief
change-over to snow at both KBMI and KCMI. Have included RASN at
both sites accordingly. Based on radar timing tools, it appears
this initial precip area will lift north of the central Illinois
terminals by 01z, followed by a lull in the precip for much of the
evening. Have therefore ended the predominant precip after 01-02z,
with only VCSH and higher VFR ceilings expected until later this
evening into the overnight hours when the main area of precip
arrives. NAM continues to spread RASN from west to east, beginning
at KPIA by around 04z, then further east to KCMI by 09z. The
precip will quickly change to all snow overnight into Sunday
morning, with visbys reduced to less than 1 mile and ceilings
dropping below 500ft. The heaviest snow will shift east of the
area by mid-afternoon, so have improved visbys slightly after
20-21z. In addition, strong N/NE winds will develop on the back
side of the departing system by late Sunday afternoon, especially
at sites along/west of the I-55 corridor. Stronger winds will be
delayed until after 00z at the eastern terminals.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ049>057-061.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Barnes






000
FXUS63 KLOT 312224
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
424 PM CST SAT JAN 31 2015

.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...
312 PM CST

MONDAY NIGHT THROUGH SATURDAY...

THE START OF THE FORECAST PERIOD WILL BE MARKED WITH EXITING
SNOWFALL WITH THE DEPARTING WINTER STORM...WHILE LAKE EFFECT SNOW
SHOWERS PERSIST NEAR THE LAKE ON MONDAY. WITH THE DEPARTING UPPER
LEVEL TROUGH AND ASSOCIATED SURFACE LOW...LOW LEVEL FLOW WILL
CONTINUE TO BACK MORE TO THE NORTH AND NORTHWEST. HOWEVER...THE
EXTENT OF THIS VEERING THROUGHOUT THE DAY WILL DETERMINE THE
PLACEMENT/DURATION OF THESE LINGERING SNOW SHOWERS WITH SOME
GUIDANCE KEEPING THE POSSIBILITY FOR LAKE EFFECT SNOW SHOWERS INTO
ILLINOIS DURING THIS TIME. EVEN IF THIS WERE TO OCCUR...NOT OVERLY
CONCERNED WITH TOO MUCH ADDITIONAL SNOWFALL DURING THIS TIME WITH
DEPARTING SYNOPTIC LIFT AND MODEST INVERSION HEIGHTS. SHIFTING HIGH
PRESSURE ACROSS THE REGION WILL ALLOW FLOW TO CONTINUE BACKING AND
ANY LINGERING SNOW SHOWERS TO PUSH FURTHER EAST LATER IN THE DAY AND
INTO MONDAY EVENING. APPROACHING SPEED MAX MONDAY NIGHT WILL HELP
STEER ANOTHER AREA OF LIGHT SNOW TOWARDS THE CWA AND DO THINK IT
WILL REACH NORTHERN ILLINOIS...BUT IT SHOULD BE DIMINISHING WITH
DISJOINTING LARGE SCALE SUPPORT AND WITH LITTLE ACCUMULATION
EXPECTED. TEMPS IN THE SINGLE DIGITS ARE LIKELY MONDAY NIGHT...WITH
INCREASING CLOUD COVER AND WHILE THE SURFACE RIDGE QUICKLY SHIFTS TO
THE SOUTHEAST.

ACTIVE WEATHER PATTERN WILL PERSIST THROUGH MID WEEK AS NORTHWEST
FLOW USHERS IN AN ADDITIONAL MID/UPPER LEVEL SYSTEM. THIS APPEARS TO
BE MORE OF A VIGOROUS SYSTEM WITH ACCUMULATING SNOW APPEARING TO BE
A POSSIBILITY LATE TUESDAY AND TUESDAY NIGHT. PRECIP SHOULD EXIT
WEDNESDAY MORNING...AS LARGE UPPER LEVEL TROUGH DIGS SOUTH ACROSS
THE REGION. STRONG PUSH OF COLDER AIR WILL OCCUR AND HELP WITH
ADDITIONAL LAKE EFFECT SNOW SHOWERS ON WEDNESDAY AS WELL AS MUCH
COLDER LOW TEMPS...WITH BELOW ZERO TEMPS APPEARING LIKELY WEDNESDAY
NIGHT AND THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW/SLEET MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW.

* WINDS WILL BE GENERALLY LIGHT FROM THE WEST FOR THE NEXT FEW
  HOURS BUT TURN NORTH THEN NORTHEAST THROUGH MID EVENING. SPEEDS
  WILL INCREASE SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS
  APPROACHING 30KT BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW MAY START OUT INTERMITTENT BEFORE SNOW
  COVERAGE INCREASES OVERNIGHT BUT 1-2SM IS LIKELY THIS EVENING.
  LOWER VSBY IS LIKELY LATE TONIGHT WITH 1/2SM OR POSSIBLY 1/4SM
  FROM EARLY SUNDAY MORNING THROUGH MUCH OF IF NOT ALL OF THE
  AFTERNOON IN SNOW AND BLOWING SNOW.

MDB

//DISCUSSION...UPDATED 22Z...

PRECIPITATION SHIELD CONTINUES TO ADVANCE NORTHEASTWARD TOWARDS
THE TERMINALS LATE THIS AFTERNOON. HAVE MAINTAINED TIMING FROM
PREVIOUS TAFS BUT AM SUSPICIOUS THAT THAT MAY BE A BIT FAST...AT
LEAST FOR STEADY PRECIP. INTERMITTENT LIGHT PRECIP MAY BE WHAT
OCCURS INITIALLY WITH LESS VSBY REDUCTION. A COLD FRONT IS MOVING
SOUTHWARD INTO THE AREA AND WILL ALLOW A STEADIER NORTHEAST LOW
LEVEL FLOW TO SET UP WHICH MAY HELP SLOW THE PRECIP ADVANCEMENT.
MAY NEED TO MAKE ADJUSTMENTS. OTHERWISE A SHORT PERIOD OF MIXED
PRECIPITATION IS POSSIBLE SO HAVE ADDED A TEMPO GROUP FOR THIS TO
THE TAFS. OTHERWISE NO CHANGES IN THINKING THROUGH THE REST OF THE
PERIOD.

MDB

FROM 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULTANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN AND
  MEDIUM CONFIDENCE THAT IT WILL BE A MIX INITIALLY.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW WITH
  THE PEAK PERIOD FROM EARLY SUNDAY MORNING THROUGH SUNDAY
  AFTERNOON.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE WILL LIKELY BE
  A PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND SHIFT.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 312224
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
424 PM CST SAT JAN 31 2015

.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...
312 PM CST

MONDAY NIGHT THROUGH SATURDAY...

THE START OF THE FORECAST PERIOD WILL BE MARKED WITH EXITING
SNOWFALL WITH THE DEPARTING WINTER STORM...WHILE LAKE EFFECT SNOW
SHOWERS PERSIST NEAR THE LAKE ON MONDAY. WITH THE DEPARTING UPPER
LEVEL TROUGH AND ASSOCIATED SURFACE LOW...LOW LEVEL FLOW WILL
CONTINUE TO BACK MORE TO THE NORTH AND NORTHWEST. HOWEVER...THE
EXTENT OF THIS VEERING THROUGHOUT THE DAY WILL DETERMINE THE
PLACEMENT/DURATION OF THESE LINGERING SNOW SHOWERS WITH SOME
GUIDANCE KEEPING THE POSSIBILITY FOR LAKE EFFECT SNOW SHOWERS INTO
ILLINOIS DURING THIS TIME. EVEN IF THIS WERE TO OCCUR...NOT OVERLY
CONCERNED WITH TOO MUCH ADDITIONAL SNOWFALL DURING THIS TIME WITH
DEPARTING SYNOPTIC LIFT AND MODEST INVERSION HEIGHTS. SHIFTING HIGH
PRESSURE ACROSS THE REGION WILL ALLOW FLOW TO CONTINUE BACKING AND
ANY LINGERING SNOW SHOWERS TO PUSH FURTHER EAST LATER IN THE DAY AND
INTO MONDAY EVENING. APPROACHING SPEED MAX MONDAY NIGHT WILL HELP
STEER ANOTHER AREA OF LIGHT SNOW TOWARDS THE CWA AND DO THINK IT
WILL REACH NORTHERN ILLINOIS...BUT IT SHOULD BE DIMINISHING WITH
DISJOINTING LARGE SCALE SUPPORT AND WITH LITTLE ACCUMULATION
EXPECTED. TEMPS IN THE SINGLE DIGITS ARE LIKELY MONDAY NIGHT...WITH
INCREASING CLOUD COVER AND WHILE THE SURFACE RIDGE QUICKLY SHIFTS TO
THE SOUTHEAST.

ACTIVE WEATHER PATTERN WILL PERSIST THROUGH MID WEEK AS NORTHWEST
FLOW USHERS IN AN ADDITIONAL MID/UPPER LEVEL SYSTEM. THIS APPEARS TO
BE MORE OF A VIGOROUS SYSTEM WITH ACCUMULATING SNOW APPEARING TO BE
A POSSIBILITY LATE TUESDAY AND TUESDAY NIGHT. PRECIP SHOULD EXIT
WEDNESDAY MORNING...AS LARGE UPPER LEVEL TROUGH DIGS SOUTH ACROSS
THE REGION. STRONG PUSH OF COLDER AIR WILL OCCUR AND HELP WITH
ADDITIONAL LAKE EFFECT SNOW SHOWERS ON WEDNESDAY AS WELL AS MUCH
COLDER LOW TEMPS...WITH BELOW ZERO TEMPS APPEARING LIKELY WEDNESDAY
NIGHT AND THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW/SLEET MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW.

* WINDS WILL BE GENERALLY LIGHT FROM THE WEST FOR THE NEXT FEW
  HOURS BUT TURN NORTH THEN NORTHEAST THROUGH MID EVENING. SPEEDS
  WILL INCREASE SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS
  APPROACHING 30KT BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW MAY START OUT INTERMITTENT BEFORE SNOW
  COVERAGE INCREASES OVERNIGHT BUT 1-2SM IS LIKELY THIS EVENING.
  LOWER VSBY IS LIKELY LATE TONIGHT WITH 1/2SM OR POSSIBLY 1/4SM
  FROM EARLY SUNDAY MORNING THROUGH MUCH OF IF NOT ALL OF THE
  AFTERNOON IN SNOW AND BLOWING SNOW.

MDB

//DISCUSSION...UPDATED 22Z...

PRECIPITATION SHIELD CONTINUES TO ADVANCE NORTHEASTWARD TOWARDS
THE TERMINALS LATE THIS AFTERNOON. HAVE MAINTAINED TIMING FROM
PREVIOUS TAFS BUT AM SUSPICIOUS THAT THAT MAY BE A BIT FAST...AT
LEAST FOR STEADY PRECIP. INTERMITTENT LIGHT PRECIP MAY BE WHAT
OCCURS INITIALLY WITH LESS VSBY REDUCTION. A COLD FRONT IS MOVING
SOUTHWARD INTO THE AREA AND WILL ALLOW A STEADIER NORTHEAST LOW
LEVEL FLOW TO SET UP WHICH MAY HELP SLOW THE PRECIP ADVANCEMENT.
MAY NEED TO MAKE ADJUSTMENTS. OTHERWISE A SHORT PERIOD OF MIXED
PRECIPITATION IS POSSIBLE SO HAVE ADDED A TEMPO GROUP FOR THIS TO
THE TAFS. OTHERWISE NO CHANGES IN THINKING THROUGH THE REST OF THE
PERIOD.

MDB

FROM 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULTANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN AND
  MEDIUM CONFIDENCE THAT IT WILL BE A MIX INITIALLY.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW WITH
  THE PEAK PERIOD FROM EARLY SUNDAY MORNING THROUGH SUNDAY
  AFTERNOON.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE WILL LIKELY BE
  A PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND SHIFT.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 312114
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 PM CST SAT JAN 31 2015


.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...
312 PM CST

MONDAY NIGHT THROUGH SATURDAY...

THE START OF THE FORECAST PERIOD WILL BE MARKED WITH EXITING
SNOWFALL WITH THE DEPARTING WINTER STORM...WHILE LAKE EFFECT SNOW
SHOWERS PERSIST NEAR THE LAKE ON MONDAY. WITH THE DEPARTING UPPER
LEVEL TROUGH AND ASSOCIATED SURFACE LOW...LOW LEVEL FLOW WILL
CONTINUE TO BACK MORE TO THE NORTH AND NORTHWEST. HOWEVER...THE
EXTENT OF THIS VEERING THROUGHOUT THE DAY WILL DETERMINE THE
PLACEMENT/DURATION OF THESE LINGERING SNOW SHOWERS WITH SOME
GUIDANCE KEEPING THE POSSIBILITY FOR LAKE EFFECT SNOW SHOWERS INTO
ILLINOIS DURING THIS TIME. EVEN IF THIS WERE TO OCCUR...NOT OVERLY
CONCERNED WITH TOO MUCH ADDITIONAL SNOWFALL DURING THIS TIME WITH
DEPARTING SYNOPTIC LIFT AND MODEST INVERSION HEIGHTS. SHIFTING HIGH
PRESSURE ACROSS THE REGION WILL ALLOW FLOW TO CONTINUE BACKING AND
ANY LINGERING SNOW SHOWERS TO PUSH FURTHER EAST LATER IN THE DAY AND
INTO MONDAY EVENING. APPROACHING SPEED MAX MONDAY NIGHT WILL HELP
STEER ANOTHER AREA OF LIGHT SNOW TOWARDS THE CWA AND DO THINK IT
WILL REACH NORTHERN ILLINOIS...BUT IT SHOULD BE DIMINISHING WITH
DISJOINTING LARGE SCALE SUPPORT AND WITH LITTLE ACCUMULATION
EXPECTED. TEMPS IN THE SINGLE DIGITS ARE LIKELY MONDAY NIGHT...WITH
INCREASING CLOUD COVER AND WHILE THE SURFACE RIDGE QUICKLY SHIFTS TO
THE SOUTHEAST.

ACTIVE WEATHER PATTERN WILL PERSIST THROUGH MID WEEK AS NORTHWEST
FLOW USHERS IN AN ADDITIONAL MID/UPPER LEVEL SYSTEM. THIS APPEARS TO
BE MORE OF A VIGOROUS SYSTEM WITH ACCUMULATING SNOW APPEARING TO BE
A POSSIBILITY LATE TUESDAY AND TUESDAY NIGHT. PRECIP SHOULD EXIT
WEDNESDAY MORNING...AS LARGE UPPER LEVEL TROUGH DIGS SOUTH ACROSS
THE REGION. STRONG PUSH OF COLDER AIR WILL OCCUR AND HELP WITH
ADDITIONAL LAKE EFFECT SNOW SHOWERS ON WEDNESDAY AS WELL AS MUCH
COLDER LOW TEMPS...WITH BELOW ZERO TEMPS APPEARING LIKELY WEDNESDAY
NIGHT AND THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 312114
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 PM CST SAT JAN 31 2015


.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...
312 PM CST

MONDAY NIGHT THROUGH SATURDAY...

THE START OF THE FORECAST PERIOD WILL BE MARKED WITH EXITING
SNOWFALL WITH THE DEPARTING WINTER STORM...WHILE LAKE EFFECT SNOW
SHOWERS PERSIST NEAR THE LAKE ON MONDAY. WITH THE DEPARTING UPPER
LEVEL TROUGH AND ASSOCIATED SURFACE LOW...LOW LEVEL FLOW WILL
CONTINUE TO BACK MORE TO THE NORTH AND NORTHWEST. HOWEVER...THE
EXTENT OF THIS VEERING THROUGHOUT THE DAY WILL DETERMINE THE
PLACEMENT/DURATION OF THESE LINGERING SNOW SHOWERS WITH SOME
GUIDANCE KEEPING THE POSSIBILITY FOR LAKE EFFECT SNOW SHOWERS INTO
ILLINOIS DURING THIS TIME. EVEN IF THIS WERE TO OCCUR...NOT OVERLY
CONCERNED WITH TOO MUCH ADDITIONAL SNOWFALL DURING THIS TIME WITH
DEPARTING SYNOPTIC LIFT AND MODEST INVERSION HEIGHTS. SHIFTING HIGH
PRESSURE ACROSS THE REGION WILL ALLOW FLOW TO CONTINUE BACKING AND
ANY LINGERING SNOW SHOWERS TO PUSH FURTHER EAST LATER IN THE DAY AND
INTO MONDAY EVENING. APPROACHING SPEED MAX MONDAY NIGHT WILL HELP
STEER ANOTHER AREA OF LIGHT SNOW TOWARDS THE CWA AND DO THINK IT
WILL REACH NORTHERN ILLINOIS...BUT IT SHOULD BE DIMINISHING WITH
DISJOINTING LARGE SCALE SUPPORT AND WITH LITTLE ACCUMULATION
EXPECTED. TEMPS IN THE SINGLE DIGITS ARE LIKELY MONDAY NIGHT...WITH
INCREASING CLOUD COVER AND WHILE THE SURFACE RIDGE QUICKLY SHIFTS TO
THE SOUTHEAST.

ACTIVE WEATHER PATTERN WILL PERSIST THROUGH MID WEEK AS NORTHWEST
FLOW USHERS IN AN ADDITIONAL MID/UPPER LEVEL SYSTEM. THIS APPEARS TO
BE MORE OF A VIGOROUS SYSTEM WITH ACCUMULATING SNOW APPEARING TO BE
A POSSIBILITY LATE TUESDAY AND TUESDAY NIGHT. PRECIP SHOULD EXIT
WEDNESDAY MORNING...AS LARGE UPPER LEVEL TROUGH DIGS SOUTH ACROSS
THE REGION. STRONG PUSH OF COLDER AIR WILL OCCUR AND HELP WITH
ADDITIONAL LAKE EFFECT SNOW SHOWERS ON WEDNESDAY AS WELL AS MUCH
COLDER LOW TEMPS...WITH BELOW ZERO TEMPS APPEARING LIKELY WEDNESDAY
NIGHT AND THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 312104
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
304 PM CST Sat Jan 31 2015

.SHORT TERM...(Tonight)
ISSUED AT 304 PM CST SAT JAN 31 2015

Latest surface map shows the low pressure with our storm system
organizing across Colorado early this afternoon, with a frontal
boundary arcing northeast along the Iowa/Minnesota border to just
north of Lake Huron. Upper wave is digging across the
Montana/Wyoming Rockies, as an upper low continues to spin just
south of Arizona. Leading edge of the precipitation shield with this
storm system has edged into the forecast area this afternoon. Some
sprinkles reported as far east as Clinton, but precipitation remains
light as there is a fair amount of dry air at the surface to
overcome. Radar mosaics showing the more organized rain back in
central Missouri and Iowa.

Forecast remains a challenge for tonight. Most of the current
guidance is suggesting precipitation being all rain much of the
evening, with a transition toward snow occurring across the northern
CWA late evening. Complicating matters is the indication by most of
the models that there will likely be a period of dry conditions
across the south half of the forecast area this evening, before
strong isentropic lift moves in from Missouri after midnight and
rapidly moistens the lower atmosphere again. The GFS came in on the
warmer end of the guidance with mainly rain into Sunday morning as
far north as I-72, while the remaining guidance rapidly cools the
column as the precipitation begins, with a switchover to snow. Have
kept a mix in the grids along I-72 past midnight before
transitioning to snow there between midnight and 3 am, with the
southeast CWA remaining mainly rain. Amount-wise, think that 3 to 5
inches of snow is likely north of a Havana to Bloomington line
tonight, with 1-2 inches along I-72, although this area remains
concerning due to the potential mixture lasting longer. Also
complicating things is temperatures above freezing in many areas,
which could limit some of the accumulations unless the snow is
falling heavy enough.


&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 304 PM CST SAT JAN 31 2015

Main focus for this forecast period continues to be the winter
weather system that will be moving across the area Sunday through
Sunday night. Over most of the area, precip should have changed over
to all snow, mainly along and north of Quincy to Paris line. Just
south of this line, precip will still be a mix of rain and snow, and
then south of I-70 it should be all rain. As the low pressure area
tracks across southern IL during the afternoon, colder air will
advect into the area and the southeast counties will change to a mix
of rain and snow, while areas north of I-70 will be all snow. Models
seem to be in fairly good agreement with the track of the system,
but differ on the temp profile during the morning hours, especially
for areas surrounding the I-72 to Danville corridor. NAM is cooler,
while the GFS is warmer and would mean more rain than snow. This
continues to be the tricky part of the forecast since the temp
profile plays into the amount of snow/snow accumulation those areas
will have. Looking at current snowfall grids, appears that Piatt,
Champaign, and Vermilion counties could reach warning criteria
snowfall Sunday, so will be adding them into the current winter
storm warning. This coincides with the eastward movement of the low
pressure area and lines up well with Indy. Counties just to the
south of this area will still remain in an advisory as the mix of
rain and snow will likely keep snowfall totals below 6 inches. Then
the 500mb trough will move across the area Sunday evening and then
bring an end to the snow by midnight.

The system will also be deepening some as it moves across the area,
and with colder air advecting into the system, the gradient will
become tighter, which means that the winds will increase and become
gusty for Sunday afternoon through Sunday night. Therefore, there
could be areas of blowing and drifting snow in the north Sunday
afternoon and then along and north of Quincy to Paris line for
Sunday evening. As the winds decrease overnight, the blowing snow
will become patchy. The areas of blowing and drifting snow will be
where most of the snow will have fallen. Believe the blowing and
drifting will be possible, even though the initial snowfall might be
heavier due to the amount of moisture. The snowfall during Sunday
afternoon and evening should be lighter given that the water content
should be drier than the earlier snowfall. Wind gusts should reach
between 30 and 35 mph during the afternoon and into the evening.

After this system, dry and cold weather is expected for Monday.
However, a clipper system is forecast to drop into the area and
bring a little bit of more snow to northern parts of the CWA for Mon
night through Tue night. Any snowfall looks to be less than one half
inch since moisture for this system will be very limited. Beyond
this, conditions will be dry through the rest of the week.

Temps will still be on the warm side Sunday, but then become much
colder for Sun night as colder air advects into the area behind the
system. Temps will remain cold for Monday and Mon night behind the
system but then warm slightly for Tue as the clipper system moves
through the area. Once the clipper moves through, colder air will
return for Wed night through Friday. Overnight low Wed night and
Thur night will be in the single digits for the northern half of the
CWA with some sites likely getting below zero. Temps will then begin
to warm again for the beginning of the weekend.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1111 AM CST SAT JAN 31 2015

Difficult forecast for this TAF set, primarily with precipitation
types and associated timing. Radar and surface reports indicating
the leading edge of the rain to our west is near KIRK, a bit later
than earlier projections, and the RAP/HRRR guidance continues with
a slower arrival. Have not gone that slow, but did delay the
arrival at all sites by a couple hours. Am uncertain on the
southern extent of associated MVFR shield, and KSPI-KCMI may stay
VFR the remainder of the afternoon. All models are showing a
warmer trend with the lower atmosphere this evening and have kept
the precip as rain longer. Starting to receive more uniform
guidance that there will be a period of dry weather late evening
and overnight across the southeast half of the state. Trended more
toward a period of VCSH instead of predominate rain from KSPI-KCMI
before the steadier precip arrives after 06Z. The models then
begin to diverge with the thermal profile. KPIA/KBMI most likely
to be all snow the remainder of the forecast period, but have
mixed precip further south until a changeover early morning,
although the GFS would suggest all rain into early afternoon. LIFR
conditions likely to develop after 07Z once the next wave of
precipitation arrives.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ049>057-061.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Geelhart






000
FXUS63 KILX 312104
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
304 PM CST Sat Jan 31 2015

.SHORT TERM...(Tonight)
ISSUED AT 304 PM CST SAT JAN 31 2015

Latest surface map shows the low pressure with our storm system
organizing across Colorado early this afternoon, with a frontal
boundary arcing northeast along the Iowa/Minnesota border to just
north of Lake Huron. Upper wave is digging across the
Montana/Wyoming Rockies, as an upper low continues to spin just
south of Arizona. Leading edge of the precipitation shield with this
storm system has edged into the forecast area this afternoon. Some
sprinkles reported as far east as Clinton, but precipitation remains
light as there is a fair amount of dry air at the surface to
overcome. Radar mosaics showing the more organized rain back in
central Missouri and Iowa.

Forecast remains a challenge for tonight. Most of the current
guidance is suggesting precipitation being all rain much of the
evening, with a transition toward snow occurring across the northern
CWA late evening. Complicating matters is the indication by most of
the models that there will likely be a period of dry conditions
across the south half of the forecast area this evening, before
strong isentropic lift moves in from Missouri after midnight and
rapidly moistens the lower atmosphere again. The GFS came in on the
warmer end of the guidance with mainly rain into Sunday morning as
far north as I-72, while the remaining guidance rapidly cools the
column as the precipitation begins, with a switchover to snow. Have
kept a mix in the grids along I-72 past midnight before
transitioning to snow there between midnight and 3 am, with the
southeast CWA remaining mainly rain. Amount-wise, think that 3 to 5
inches of snow is likely north of a Havana to Bloomington line
tonight, with 1-2 inches along I-72, although this area remains
concerning due to the potential mixture lasting longer. Also
complicating things is temperatures above freezing in many areas,
which could limit some of the accumulations unless the snow is
falling heavy enough.


&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 304 PM CST SAT JAN 31 2015

Main focus for this forecast period continues to be the winter
weather system that will be moving across the area Sunday through
Sunday night. Over most of the area, precip should have changed over
to all snow, mainly along and north of Quincy to Paris line. Just
south of this line, precip will still be a mix of rain and snow, and
then south of I-70 it should be all rain. As the low pressure area
tracks across southern IL during the afternoon, colder air will
advect into the area and the southeast counties will change to a mix
of rain and snow, while areas north of I-70 will be all snow. Models
seem to be in fairly good agreement with the track of the system,
but differ on the temp profile during the morning hours, especially
for areas surrounding the I-72 to Danville corridor. NAM is cooler,
while the GFS is warmer and would mean more rain than snow. This
continues to be the tricky part of the forecast since the temp
profile plays into the amount of snow/snow accumulation those areas
will have. Looking at current snowfall grids, appears that Piatt,
Champaign, and Vermilion counties could reach warning criteria
snowfall Sunday, so will be adding them into the current winter
storm warning. This coincides with the eastward movement of the low
pressure area and lines up well with Indy. Counties just to the
south of this area will still remain in an advisory as the mix of
rain and snow will likely keep snowfall totals below 6 inches. Then
the 500mb trough will move across the area Sunday evening and then
bring an end to the snow by midnight.

The system will also be deepening some as it moves across the area,
and with colder air advecting into the system, the gradient will
become tighter, which means that the winds will increase and become
gusty for Sunday afternoon through Sunday night. Therefore, there
could be areas of blowing and drifting snow in the north Sunday
afternoon and then along and north of Quincy to Paris line for
Sunday evening. As the winds decrease overnight, the blowing snow
will become patchy. The areas of blowing and drifting snow will be
where most of the snow will have fallen. Believe the blowing and
drifting will be possible, even though the initial snowfall might be
heavier due to the amount of moisture. The snowfall during Sunday
afternoon and evening should be lighter given that the water content
should be drier than the earlier snowfall. Wind gusts should reach
between 30 and 35 mph during the afternoon and into the evening.

After this system, dry and cold weather is expected for Monday.
However, a clipper system is forecast to drop into the area and
bring a little bit of more snow to northern parts of the CWA for Mon
night through Tue night. Any snowfall looks to be less than one half
inch since moisture for this system will be very limited. Beyond
this, conditions will be dry through the rest of the week.

Temps will still be on the warm side Sunday, but then become much
colder for Sun night as colder air advects into the area behind the
system. Temps will remain cold for Monday and Mon night behind the
system but then warm slightly for Tue as the clipper system moves
through the area. Once the clipper moves through, colder air will
return for Wed night through Friday. Overnight low Wed night and
Thur night will be in the single digits for the northern half of the
CWA with some sites likely getting below zero. Temps will then begin
to warm again for the beginning of the weekend.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1111 AM CST SAT JAN 31 2015

Difficult forecast for this TAF set, primarily with precipitation
types and associated timing. Radar and surface reports indicating
the leading edge of the rain to our west is near KIRK, a bit later
than earlier projections, and the RAP/HRRR guidance continues with
a slower arrival. Have not gone that slow, but did delay the
arrival at all sites by a couple hours. Am uncertain on the
southern extent of associated MVFR shield, and KSPI-KCMI may stay
VFR the remainder of the afternoon. All models are showing a
warmer trend with the lower atmosphere this evening and have kept
the precip as rain longer. Starting to receive more uniform
guidance that there will be a period of dry weather late evening
and overnight across the southeast half of the state. Trended more
toward a period of VCSH instead of predominate rain from KSPI-KCMI
before the steadier precip arrives after 06Z. The models then
begin to diverge with the thermal profile. KPIA/KBMI most likely
to be all snow the remainder of the forecast period, but have
mixed precip further south until a changeover early morning,
although the GFS would suggest all rain into early afternoon. LIFR
conditions likely to develop after 07Z once the next wave of
precipitation arrives.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ049>057-061.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Geelhart







000
FXUS63 KLOT 311957
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
157 PM CST SAT JAN 31 2015

.UPDATE...

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032...6 PM SATURDAY TO
     MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 311957
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
157 PM CST SAT JAN 31 2015

.UPDATE...

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032...6 PM SATURDAY TO
     MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311938
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 PM CST SAT JAN 31 2015

.UPDATE...

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311938
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 PM CST SAT JAN 31 2015

.UPDATE...

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311938
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 PM CST SAT JAN 31 2015

.UPDATE...

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311938
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 PM CST SAT JAN 31 2015

.UPDATE...

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311801
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1201 PM CST SAT JAN 31 2015

.UPDATE...1032 AM CST

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH 20Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311801
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1201 PM CST SAT JAN 31 2015

.UPDATE...1032 AM CST

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH 20Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 311722
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1122 AM CST Sat Jan 31 2015

.UPDATE...
ISSUED AT 1037 AM CST SAT JAN 31 2015

Radar mosaics overdoing things a bit late this morning, with
surface reports indicating the precipitation just coming into
central Missouri. Have trended a bit slower with the precipitation
development this afternoon across our area, but have likely PoP`s
by late afternoon all the way east to I-57. Temperatures largely
on track and required only minor adjustments.

Early look at the NAM and GFS for the rest of the weekend shows
some concerns with the thermal profiles on the southern edge of
the snow shield. NAM has shifted a bit south and keeps all snow on
Sunday north of I-72, while the GFS is solidly all rain along I-72
into Sunday afternoon. Also have concerns with the dry slot that
both models and the high-res ARW/NMM are showing across the
southeast third of the CWA a good part of the overnight hours.
Have not made any adjustments quite yet, but will be evaluating
this further over the next couple hours.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT JAN 31 2015

Quiet weather is expected to start the day across central and
southeast Illinois. A ridge of high pressure, currently paralleling
the Ohio River Valley, will continue to pull away from the area.
This will allow a storm system, starting to get organized over the
southwest United States, to approach. Decent WAA/isentropic lift
ahead of the approaching storm will result in steadily
increasing/thickening cloud cover this morning. Rain will begin to
spread across the forecast area from southwest to northeast this
afternoon. A rain/snow mix can`t be ruled out by late afternoon
across our far northwest counties, mainly Knox, Stark, and Marshall,
but no snow accumulation is anticipated before tonight. The
southerly winds will push temperatures above normal, despite the
cloud cover and precipitation breaking out, with highs near 40
degrees in most areas.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT JAN 31 2015

Surface wave moving out of the desert SW and phasing with an upper
level trof in the more northern portion of the 500mb flow over the
CONUS to bring the next winter storm for the Midwest Saturday and
Sunday.  Models continue to track a little further north with the
solutions...putting more and more warm air ahead of the low.  This
warmer trend ahead of the system will keep the precipitation mainly
rain even into the evening hours.  Cold air is not as deep and
abundant with this system, and the strong southerly flow in advance
of the sfc low keeping the low levels warm enough for rain.  NAM
Bufkit soundings not switching over to all snow for PIA until
between 03-06Z.  However, have rain/snow mix for the evening, but
temps very at or above freezing through most of the evening up to
midnight will limit the accumulations and/or make for a very slushy
wet mix.  Once the low draws closer and more cold air is pulled into
the system, the changeover to snow will become more widespread
across the area, mainly north of the I-70 corridor.  Areas between
I-70 and roughly I-72 will see a mix a bit longer as well, but still
changing over to mostly snow by Sunday.  Snow lingering into Sunday
evening before ending by Monday morning.

Significant accumulations are expected with this storm...over an
extended period of time.  Winter Storm Warning is confined to a
Rushville to Bloomington line. Traditional Winter Storm Warning
criteria will be very close...though 6"-8" are expected in the
warned area in TOTAL...the snow will accumulate over an extended
period of time-18 to 24 hours-- with the best snowfall accumulations
expected between early Sunday morning and Sunday evening.  The
Winter Weather Advisory south of the warning up to, but not
including, the I-70 corridor will also see the accumulations over a
longer duration event.  Although the southeast likely to see mostly
rain, some snow accumulations will drop south of I-70 by Monday
morning as well.

Phasing of this sfc system with an open wave aloft resulting in
weaker dynamics in the bigger picture and a slower deepening of the
low.  Lift at any given time good to moderate, but limited by lack
of deeper organization. Isentropic lift definitely there on 305-320K
sfcs, but never for long and angle of winds to gradient closer to 45
than to perpendicular. Models struggling with over deepening of the
system and potentially with the snowfall accumulations being
overdone somewhat with the warmer air moving into the system.  That
being said...even reducing the snowfall totals from model QPF...over
such a long duration with a slow moving system, the totals are still
in warning/advisory criteria for much of the Midwest.

Winds increasing as the storm moves through, particularly on Sunday
afternoon could result in some blowing snow over the northern tier
of ILX, although the snow will initially be more wet and heavy...as
the storm goes on the SLRs will increase and snow be more prone to
blowing and drifting.

Cold air moving in behind the system will result in a very chilly
Monday and another quick wave Monday will bring another chance for
some snow mainly across the northern third of the state.
Accumulations are expected to be low at this point with that
system.  Beyond that, the forecast is relatively quiet through the
work week with moderate temperatures until deeper cold air moves
into the region dropping high temps at the end of the week into the
teens and 20s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1111 AM CST SAT JAN 31 2015

Difficult forecast for this TAF set, primarily with precipitation
types and associated timing. Radar and surface reports indicating
the leading edge of the rain to our west is near KIRK, a bit later
than earlier projections, and the RAP/HRRR guidance continues with
a slower arrival. Have not gone that slow, but did delay the
arrival at all sites by a couple hours. Am uncertain on the
southern extent of associated MVFR shield, and KSPI-KCMI may stay
VFR the remainder of the afternoon. All models are showing a
warmer trend with the lower atmosphere this evening and have kept
the precip as rain longer. Starting to receive more uniform
guidance that there will be a period of dry weather late evening
and overnight across the southeast half of the state. Trended more
toward a period of VCSH instead of predominate rain from KSPI-KCMI
before the steadier precip arrives after 06Z. The models then
begin to diverge with the thermal profile. KPIA/KBMI most likely
to be all snow the remainder of the forecast period, but have
mixed precip further south until a changeover early morning,
although the GFS would suggest all rain into early afternoon. LIFR
conditions likely to develop after 07Z once the next wave of
precipitation arrives.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>043-047-048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ044>046-049>057-061.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...HJS
AVIATION...Geelhart







000
FXUS63 KILX 311722
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1122 AM CST Sat Jan 31 2015

.UPDATE...
ISSUED AT 1037 AM CST SAT JAN 31 2015

Radar mosaics overdoing things a bit late this morning, with
surface reports indicating the precipitation just coming into
central Missouri. Have trended a bit slower with the precipitation
development this afternoon across our area, but have likely PoP`s
by late afternoon all the way east to I-57. Temperatures largely
on track and required only minor adjustments.

Early look at the NAM and GFS for the rest of the weekend shows
some concerns with the thermal profiles on the southern edge of
the snow shield. NAM has shifted a bit south and keeps all snow on
Sunday north of I-72, while the GFS is solidly all rain along I-72
into Sunday afternoon. Also have concerns with the dry slot that
both models and the high-res ARW/NMM are showing across the
southeast third of the CWA a good part of the overnight hours.
Have not made any adjustments quite yet, but will be evaluating
this further over the next couple hours.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT JAN 31 2015

Quiet weather is expected to start the day across central and
southeast Illinois. A ridge of high pressure, currently paralleling
the Ohio River Valley, will continue to pull away from the area.
This will allow a storm system, starting to get organized over the
southwest United States, to approach. Decent WAA/isentropic lift
ahead of the approaching storm will result in steadily
increasing/thickening cloud cover this morning. Rain will begin to
spread across the forecast area from southwest to northeast this
afternoon. A rain/snow mix can`t be ruled out by late afternoon
across our far northwest counties, mainly Knox, Stark, and Marshall,
but no snow accumulation is anticipated before tonight. The
southerly winds will push temperatures above normal, despite the
cloud cover and precipitation breaking out, with highs near 40
degrees in most areas.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT JAN 31 2015

Surface wave moving out of the desert SW and phasing with an upper
level trof in the more northern portion of the 500mb flow over the
CONUS to bring the next winter storm for the Midwest Saturday and
Sunday.  Models continue to track a little further north with the
solutions...putting more and more warm air ahead of the low.  This
warmer trend ahead of the system will keep the precipitation mainly
rain even into the evening hours.  Cold air is not as deep and
abundant with this system, and the strong southerly flow in advance
of the sfc low keeping the low levels warm enough for rain.  NAM
Bufkit soundings not switching over to all snow for PIA until
between 03-06Z.  However, have rain/snow mix for the evening, but
temps very at or above freezing through most of the evening up to
midnight will limit the accumulations and/or make for a very slushy
wet mix.  Once the low draws closer and more cold air is pulled into
the system, the changeover to snow will become more widespread
across the area, mainly north of the I-70 corridor.  Areas between
I-70 and roughly I-72 will see a mix a bit longer as well, but still
changing over to mostly snow by Sunday.  Snow lingering into Sunday
evening before ending by Monday morning.

Significant accumulations are expected with this storm...over an
extended period of time.  Winter Storm Warning is confined to a
Rushville to Bloomington line. Traditional Winter Storm Warning
criteria will be very close...though 6"-8" are expected in the
warned area in TOTAL...the snow will accumulate over an extended
period of time-18 to 24 hours-- with the best snowfall accumulations
expected between early Sunday morning and Sunday evening.  The
Winter Weather Advisory south of the warning up to, but not
including, the I-70 corridor will also see the accumulations over a
longer duration event.  Although the southeast likely to see mostly
rain, some snow accumulations will drop south of I-70 by Monday
morning as well.

Phasing of this sfc system with an open wave aloft resulting in
weaker dynamics in the bigger picture and a slower deepening of the
low.  Lift at any given time good to moderate, but limited by lack
of deeper organization. Isentropic lift definitely there on 305-320K
sfcs, but never for long and angle of winds to gradient closer to 45
than to perpendicular. Models struggling with over deepening of the
system and potentially with the snowfall accumulations being
overdone somewhat with the warmer air moving into the system.  That
being said...even reducing the snowfall totals from model QPF...over
such a long duration with a slow moving system, the totals are still
in warning/advisory criteria for much of the Midwest.

Winds increasing as the storm moves through, particularly on Sunday
afternoon could result in some blowing snow over the northern tier
of ILX, although the snow will initially be more wet and heavy...as
the storm goes on the SLRs will increase and snow be more prone to
blowing and drifting.

Cold air moving in behind the system will result in a very chilly
Monday and another quick wave Monday will bring another chance for
some snow mainly across the northern third of the state.
Accumulations are expected to be low at this point with that
system.  Beyond that, the forecast is relatively quiet through the
work week with moderate temperatures until deeper cold air moves
into the region dropping high temps at the end of the week into the
teens and 20s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1111 AM CST SAT JAN 31 2015

Difficult forecast for this TAF set, primarily with precipitation
types and associated timing. Radar and surface reports indicating
the leading edge of the rain to our west is near KIRK, a bit later
than earlier projections, and the RAP/HRRR guidance continues with
a slower arrival. Have not gone that slow, but did delay the
arrival at all sites by a couple hours. Am uncertain on the
southern extent of associated MVFR shield, and KSPI-KCMI may stay
VFR the remainder of the afternoon. All models are showing a
warmer trend with the lower atmosphere this evening and have kept
the precip as rain longer. Starting to receive more uniform
guidance that there will be a period of dry weather late evening
and overnight across the southeast half of the state. Trended more
toward a period of VCSH instead of predominate rain from KSPI-KCMI
before the steadier precip arrives after 06Z. The models then
begin to diverge with the thermal profile. KPIA/KBMI most likely
to be all snow the remainder of the forecast period, but have
mixed precip further south until a changeover early morning,
although the GFS would suggest all rain into early afternoon. LIFR
conditions likely to develop after 07Z once the next wave of
precipitation arrives.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>043-047-048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ044>046-049>057-061.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...HJS
AVIATION...Geelhart






000
FXUS63 KLOT 311643
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1043 AM CST SAT JAN 31 2015

.UPDATE...
1032 AM CST

CURRENTLY GOING OVER THE LATEST FORECAST GUIDANCE. A FIRST LOOK
AT THE 12 UTC GFS INCREASES MY CONCERNS FOR HEAVY SNOW ACROSS MUCH
OF MY AREA TONIGHT INTO SUNDAY. HOWEVER...PRECIP TYPE ISSUES
MENTIONED IN THE PREVIOUS DISCUSSION COULD COMPLICATED THINGS
ACROSS MY FAR SOUTHERN COUNTIES...AS THE LATEST GUIDANCE SUGGESTS
THE 850 MB LOW MAY TRACK RIGHT ACROSS EAST CENTRAL ILLINOIS SUNDAY
AFTERNOON. AS A RESULT...THIS COULD IMPACT SNOW AMOUNTS ACROSS MY
FAR SOUTH.

I AM ALSO BECOMING MORE CONCERNED FOR THE POTENTIAL OF
BLIZZARD CONDITIONS SUNDAY AND SUNDAY EVENING...ESPECIALLY GIVEN
THE TREND FOR A STRONGER SYSTEM. THE 12 UTC RUN OF THE GFS
SUGGESTS WIND ADVISORY LEVEL WINDS...WITH GUSTS POTENTIALLY UP
AROUND 40 KT. IF THESE TYPE OF WINDS MATERIALIZE...WHITE OUT
CONDITIONS COULD CERTAINLY BECOME AN ISSUE. IN ANY
EVENT...CONFIDENCE IS INCREASING THAT MOST OF MY AREA WILL
EXPERIENCE A MAJOR WINTER STORM...WITH UP TO A FOOT OF SNOW
POSSIBLE.

KJB

&&

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* NONE THROUGH LATE AFTERNOON.

* CIGS LOWERING TO MVFR BY LATE AFTERNOON AND THEN TO IFR WITH
  SHORTLY AFTER SNOW ONSET. CIGS LIKELY TO REMAIN IFR THROUGH THE
  DURATION OF THE SNOW.

* TIMING OF SNOW...STARTING EARLY EVENING AND THEN PERSISTING
  UNTIL AFTER THE TAF PERIOD.

* IFR VIS WITH ONSET OF SNOW. VIS WILL LIKELY BE VARIABLE WITH
  PERIODS OF HEAVIER AND LIGHTER SNOW.

* WINDS WILL VEER FROM SWLY TO NELY THIS EVENING. NELY WINDS
  EXPECTED TO STRENGTHEN SUNDAY MORNING...WITH GUSTS TO 30KT.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

QUIET CONDITIONS WILL CONTINUE THROUGH LATE THIS AFTERNOON. A
WINTER STORM DEVELOPING OVER THE SWRN CONUS WILL TRACK
NORTHEAST...WITH PCPN OVERSPREADING THE REGION LATE THIS AFTERNOON
AND EARLY THIS EVENING. INITIALLY...TEMPERATURES SHOULD BE HIGH
ENOUGH FOR THE INITIAL PCPN TO BE RAIN OR A RAIN/SNOW MIX...BUT
TEMPERATURES WILL DROP AND PCPN SHOULD QUICKLY CHANGE OVER TO ALL
SNOW BY LATE EVENING. THIS SYSTEM IS SETTING UP TO BE LONG
DURATION EVENT WITH SNOW FALLING THROUGH LATE SUNDAY NIGHT OR INTO
EARLY MONDAY MORNING. THE PERIOD OF HEAVIEST SNOW SHOULD BE
FROM AROUND EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON
WHEN VISIBILITY MAY DROP TO BELOW 3/4SM AT TIME WITH SNOWFALL
RATES OF 1 INCH PER HOUR OR GREATER. WITH NELY WINDS RAMPING UP
THROUGH THE DAY ON SUNDAY...WITH GUSTS OF 25-30KT...BLOWING AND
DRIFTING SNOW WILL ALSO BE A CONCERN. THERE IS ALSO A CHANCE FOR
SOME LINGERING LAKE EFFECT SNOW SHOWERS ON MONDAY MORNING...BUT
THERE IS SOME UNCERTAINTY AS TO WHERE A LAKE EFFECT SNOW BAND
WOULD DEVELOP. THE LATEST GUIDANCE SUGGESTS THAT THE MAIN BAND OF
LAKE EFFECT SNOW WILL POINT INTO NWRN INDIANA...WITH GYY THE ONLY
TAF SITE IMPACTED...BUT THERE IS STILL A CHANCE FOR SOME SCT LAKE
EFFECT SNOW SHOWERS OVER NERN IL.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KILX 311639
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1039 AM CST Sat Jan 31 2015

.UPDATE...
ISSUED AT 1037 AM CST SAT JAN 31 2015

Radar mosaics overdoing things a bit late this morning, with
surface reports indicating the precipitation just coming into
central Missouri. Have trended a bit slower with the precipitation
development this afternoon across our area, but have likely PoP`s
by late afternoon all the way east to I-57. Temperatures largely
on track and required only minor adjustments.

Early look at the NAM and GFS for the rest of the weekend shows
some concerns with the thermal profiles on the southern edge of
the snow shield. NAM has shifted a bit south and keeps all snow on
Sunday north of I-72, while the GFS is solidly all rain along I-72
into Sunday afternoon. Also have concerns with the dry slot that
both models and the high-res ARW/NMM are showing across the
southeast third of the CWA a good part of the overnight hours.
Have not made any adjustments quite yet, but will be evaluating
this further over the next couple hours.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT JAN 31 2015

Quiet weather is expected to start the day across central and
southeast Illinois. A ridge of high pressure, currently paralleling
the Ohio River Valley, will continue to pull away from the area.
This will allow a storm system, starting to get organized over the
southwest United States, to approach. Decent WAA/isentropic lift
ahead of the approaching storm will result in steadily
increasing/thickening cloud cover this morning. Rain will begin to
spread across the forecast area from southwest to northeast this
afternoon. A rain/snow mix can`t be ruled out by late afternoon
across our far northwest counties, mainly Knox, Stark, and Marshall,
but no snow accumulation is anticipated before tonight. The
southerly winds will push temperatures above normal, despite the
cloud cover and precipitation breaking out, with highs near 40
degrees in most areas.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT JAN 31 2015

Surface wave moving out of the desert SW and phasing with an upper
level trof in the more northern portion of the 500mb flow over the
CONUS to bring the next winter storm for the Midwest Saturday and
Sunday.  Models continue to track a little further north with the
solutions...putting more and more warm air ahead of the low.  This
warmer trend ahead of the system will keep the precipitation mainly
rain even into the evening hours.  Cold air is not as deep and
abundant with this system, and the strong southerly flow in advance
of the sfc low keeping the low levels warm enough for rain.  NAM
Bufkit soundings not switching over to all snow for PIA until
between 03-06z.  However, have rain/snow mix for the evening, but
temps very at or above freezing through most of the evening up to
midnight will limit the accumulations and/or make for a very slushy
wet mix.  Once the low draws closer and more cold air is pulled into
the system, the changeover to snow will become more widespread
across the area, mainly north of the I-70 corridor.  Areas between
I-70 and roughly I-72 will see a mix a bit longer as well, but still
changing over to mostly snow by Sunday.  Snow lingering into Sunday
evening before ending by Monday morning.

Significant accumulations are expected with this storm...over an
extended period of time.  Winter Storm Warning is confined to a
Rushville to Bloomington line. Traditional Winter Storm Warning
criteria will be very close...though 6"-8" are expected in the
warned area in TOTAL...the snow will accumulate over an extended
period of time-18 to 24 hours-- with the best snowfall accumulations
expected between early Sunday morning and Sunday evening.  The
Winter Weather Advisory south of the warning up to, but not
including, the I-70 corridor will also see the accumulations over a
longer duration event.  Although the southeast likely to see mostly
rain, some snow accumulations will drop south of I-70 by Monday
morning as well.

Phasing of this sfc system with an open wave aloft resulting in
weaker dynamics in the bigger picture and a slower deepening of the
low.  Lift at any given time good to moderate, but limited by lack
of deeper organization. Isentropic lift definitely there on 305-320K
sfcs, but never for long and angle of winds to gradient closer to 45
than to perpendicular. Models struggling with over deepening of the
system and potentially with the snowfall accumulations being
overdone somewhat with the warmer air moving into the system.  That
being said...even reducing the snowfall totals from model QPF...over
such a long duration with a slow moving system, the totals are still
in warning/advisory criteria for much of the Midwest.

Winds increasing as the storm moves through, particularly on Sunday
afternoon could result in some blowing snow over the northern tier
of ILX, although the snow will initially be more wet and heavy...as
the storm goes on the SLRs will increase and snow be more prone to
blowing and drifting.

Cold air moving in behind the system will result in a very chilly
Monday and another quick wave Monday will bring another chance for
some snow mainly across the northern third of the state.
Accumulations are expected to be low at this point with that
system.  Beyond that, the forecast is relatively quiet through the
work week with moderate temperatures until deeper cold air moves
into the region dropping high temps at the end of the week into the
teens and 20s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 520 AM CST SAT JAN 31 2015

Conditions across the central Illinois terminals will start out
quiet/VFR as departing high pressure slowly loses its grip on the
area. This will allow a rapid thickening/lowering of the clouds as
a storm system approaches from the west. Rain will begin to break
out from these thicker clouds later this afternoon, with light
rain expected to develop as well. The persistent precipitation
will eventually see conditions degrade to IFR this evening. The
precipitation will also gradually mix with and change over to snow
as cooler air begins to filter into the area.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>043-047-048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ044>046-049>057-061.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...HJS
AVIATION...Bak






000
FXUS63 KILX 311639
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1039 AM CST Sat Jan 31 2015

.UPDATE...
ISSUED AT 1037 AM CST SAT JAN 31 2015

Radar mosaics overdoing things a bit late this morning, with
surface reports indicating the precipitation just coming into
central Missouri. Have trended a bit slower with the precipitation
development this afternoon across our area, but have likely PoP`s
by late afternoon all the way east to I-57. Temperatures largely
on track and required only minor adjustments.

Early look at the NAM and GFS for the rest of the weekend shows
some concerns with the thermal profiles on the southern edge of
the snow shield. NAM has shifted a bit south and keeps all snow on
Sunday north of I-72, while the GFS is solidly all rain along I-72
into Sunday afternoon. Also have concerns with the dry slot that
both models and the high-res ARW/NMM are showing across the
southeast third of the CWA a good part of the overnight hours.
Have not made any adjustments quite yet, but will be evaluating
this further over the next couple hours.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT JAN 31 2015

Quiet weather is expected to start the day across central and
southeast Illinois. A ridge of high pressure, currently paralleling
the Ohio River Valley, will continue to pull away from the area.
This will allow a storm system, starting to get organized over the
southwest United States, to approach. Decent WAA/isentropic lift
ahead of the approaching storm will result in steadily
increasing/thickening cloud cover this morning. Rain will begin to
spread across the forecast area from southwest to northeast this
afternoon. A rain/snow mix can`t be ruled out by late afternoon
across our far northwest counties, mainly Knox, Stark, and Marshall,
but no snow accumulation is anticipated before tonight. The
southerly winds will push temperatures above normal, despite the
cloud cover and precipitation breaking out, with highs near 40
degrees in most areas.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT JAN 31 2015

Surface wave moving out of the desert SW and phasing with an upper
level trof in the more northern portion of the 500mb flow over the
CONUS to bring the next winter storm for the Midwest Saturday and
Sunday.  Models continue to track a little further north with the
solutions...putting more and more warm air ahead of the low.  This
warmer trend ahead of the system will keep the precipitation mainly
rain even into the evening hours.  Cold air is not as deep and
abundant with this system, and the strong southerly flow in advance
of the sfc low keeping the low levels warm enough for rain.  NAM
Bufkit soundings not switching over to all snow for PIA until
between 03-06z.  However, have rain/snow mix for the evening, but
temps very at or above freezing through most of the evening up to
midnight will limit the accumulations and/or make for a very slushy
wet mix.  Once the low draws closer and more cold air is pulled into
the system, the changeover to snow will become more widespread
across the area, mainly north of the I-70 corridor.  Areas between
I-70 and roughly I-72 will see a mix a bit longer as well, but still
changing over to mostly snow by Sunday.  Snow lingering into Sunday
evening before ending by Monday morning.

Significant accumulations are expected with this storm...over an
extended period of time.  Winter Storm Warning is confined to a
Rushville to Bloomington line. Traditional Winter Storm Warning
criteria will be very close...though 6"-8" are expected in the
warned area in TOTAL...the snow will accumulate over an extended
period of time-18 to 24 hours-- with the best snowfall accumulations
expected between early Sunday morning and Sunday evening.  The
Winter Weather Advisory south of the warning up to, but not
including, the I-70 corridor will also see the accumulations over a
longer duration event.  Although the southeast likely to see mostly
rain, some snow accumulations will drop south of I-70 by Monday
morning as well.

Phasing of this sfc system with an open wave aloft resulting in
weaker dynamics in the bigger picture and a slower deepening of the
low.  Lift at any given time good to moderate, but limited by lack
of deeper organization. Isentropic lift definitely there on 305-320K
sfcs, but never for long and angle of winds to gradient closer to 45
than to perpendicular. Models struggling with over deepening of the
system and potentially with the snowfall accumulations being
overdone somewhat with the warmer air moving into the system.  That
being said...even reducing the snowfall totals from model QPF...over
such a long duration with a slow moving system, the totals are still
in warning/advisory criteria for much of the Midwest.

Winds increasing as the storm moves through, particularly on Sunday
afternoon could result in some blowing snow over the northern tier
of ILX, although the snow will initially be more wet and heavy...as
the storm goes on the SLRs will increase and snow be more prone to
blowing and drifting.

Cold air moving in behind the system will result in a very chilly
Monday and another quick wave Monday will bring another chance for
some snow mainly across the northern third of the state.
Accumulations are expected to be low at this point with that
system.  Beyond that, the forecast is relatively quiet through the
work week with moderate temperatures until deeper cold air moves
into the region dropping high temps at the end of the week into the
teens and 20s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 520 AM CST SAT JAN 31 2015

Conditions across the central Illinois terminals will start out
quiet/VFR as departing high pressure slowly loses its grip on the
area. This will allow a rapid thickening/lowering of the clouds as
a storm system approaches from the west. Rain will begin to break
out from these thicker clouds later this afternoon, with light
rain expected to develop as well. The persistent precipitation
will eventually see conditions degrade to IFR this evening. The
precipitation will also gradually mix with and change over to snow
as cooler air begins to filter into the area.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>043-047-048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ044>046-049>057-061.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...HJS
AVIATION...Bak







000
FXUS63 KLOT 311413
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
813 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NONE THROUGH LATE AFTERNOON.

* CIGS LOWERING TO MVFR BY LATE AFTERNOON AND THEN TO IFR WITH
  SHORTLY AFTER SNOW ONSET. CIGS LIKELY TO REMAIN IFR THROUGH THE
  DURATION OF THE SNOW.

* TIMING OF SNOW...STARTING EARLY EVENING AND THEN PERSISTING
  UNTIL AFTER THE TAF PERIOD.

* IFR VIS WITH ONSET OF SNOW. VIS WILL LIKELY BE VARIABLE WITH
  PERIODS OF HEAVIER AND LIGHTER SNOW.

* WINDS WILL VEER FROM SWLY TO NELY THIS EVENING. NELY WINDS
  EXPECTED TO STRENGTHEN SUNDAY MORNING...WITH GUSTS TO 30KT.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

QUIET CONDITIONS WILL CONTINUE THROUGH LATE THIS AFTERNOON. A
WINTER STORM DEVELOPING OVER THE SWRN CONUS WILL TRACK
NORTHEAST...WITH PCPN OVERSPREADING THE REGION LATE THIS AFTERNOON
AND EARLY THIS EVENING. INITIALLY...TEMPERATURES SHOULD BE HIGH
ENOUGH FOR THE INITIAL PCPN TO BE RAIN OR A RAIN/SNOW MIX...BUT
TEMPERATURES WILL DROP AND PCPN SHOULD QUICKLY CHANGE OVER TO ALL
SNOW BY LATE EVENING. THIS SYSTEM IS SETTING UP TO BE LONG
DURATION EVENT WITH SNOW FALLING THROUGH LATE SUNDAY NIGHT OR INTO
EARLY MONDAY MORNING. THE PERIOD OF HEAVIEST SNOW SHOULD BE
FROM AROUND EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON
WHEN VISIBILITY MAY DROP TO BELOW 3/4SM AT TIME WITH SNOWFALL
RATES OF 1 INCH PER HOUR OR GREATER. WITH NELY WINDS RAMPING UP
THROUGH THE DAY ON SUNDAY...WITH GUSTS OF 25-30KT...BLOWING AND
DRIFTING SNOW WILL ALSO BE A CONCERN. THERE IS ALSO A CHANCE FOR
SOME LINGERING LAKE EFFECT SNOW SHOWERS ON MONDAY MORNING...BUT
THERE IS SOME UNCERTAINTY AS TO WHERE A LAKE EFFECT SNOW BAND
WOULD DEVELOP. THE LATEST GUIDANCE SUGGESTS THAT THE MAIN BAND OF
LAKE EFFECT SNOW WILL POINT INTO NWRN INDIANA...WITH GYY THE ONLY
TAF SITE IMPACTED...BUT THERE IS STILL A CHANCE FOR SOME SCT LAKE
EFFECT SNOW SHOWERS OVER NERN IL.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311413
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
813 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NONE THROUGH LATE AFTERNOON.

* CIGS LOWERING TO MVFR BY LATE AFTERNOON AND THEN TO IFR WITH
  SHORTLY AFTER SNOW ONSET. CIGS LIKELY TO REMAIN IFR THROUGH THE
  DURATION OF THE SNOW.

* TIMING OF SNOW...STARTING EARLY EVENING AND THEN PERSISTING
  UNTIL AFTER THE TAF PERIOD.

* IFR VIS WITH ONSET OF SNOW. VIS WILL LIKELY BE VARIABLE WITH
  PERIODS OF HEAVIER AND LIGHTER SNOW.

* WINDS WILL VEER FROM SWLY TO NELY THIS EVENING. NELY WINDS
  EXPECTED TO STRENGTHEN SUNDAY MORNING...WITH GUSTS TO 30KT.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

QUIET CONDITIONS WILL CONTINUE THROUGH LATE THIS AFTERNOON. A
WINTER STORM DEVELOPING OVER THE SWRN CONUS WILL TRACK
NORTHEAST...WITH PCPN OVERSPREADING THE REGION LATE THIS AFTERNOON
AND EARLY THIS EVENING. INITIALLY...TEMPERATURES SHOULD BE HIGH
ENOUGH FOR THE INITIAL PCPN TO BE RAIN OR A RAIN/SNOW MIX...BUT
TEMPERATURES WILL DROP AND PCPN SHOULD QUICKLY CHANGE OVER TO ALL
SNOW BY LATE EVENING. THIS SYSTEM IS SETTING UP TO BE LONG
DURATION EVENT WITH SNOW FALLING THROUGH LATE SUNDAY NIGHT OR INTO
EARLY MONDAY MORNING. THE PERIOD OF HEAVIEST SNOW SHOULD BE
FROM AROUND EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON
WHEN VISIBILITY MAY DROP TO BELOW 3/4SM AT TIME WITH SNOWFALL
RATES OF 1 INCH PER HOUR OR GREATER. WITH NELY WINDS RAMPING UP
THROUGH THE DAY ON SUNDAY...WITH GUSTS OF 25-30KT...BLOWING AND
DRIFTING SNOW WILL ALSO BE A CONCERN. THERE IS ALSO A CHANCE FOR
SOME LINGERING LAKE EFFECT SNOW SHOWERS ON MONDAY MORNING...BUT
THERE IS SOME UNCERTAINTY AS TO WHERE A LAKE EFFECT SNOW BAND
WOULD DEVELOP. THE LATEST GUIDANCE SUGGESTS THAT THE MAIN BAND OF
LAKE EFFECT SNOW WILL POINT INTO NWRN INDIANA...WITH GYY THE ONLY
TAF SITE IMPACTED...BUT THERE IS STILL A CHANCE FOR SOME SCT LAKE
EFFECT SNOW SHOWERS OVER NERN IL.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NONE THROUGH LATE AFTERNOON.

* CIGS LOWERING TO MVFR BY LATE AFTERNOON AND THEN TO IFR WITH
  SHORTLY AFTER SNOW ONSET. CIGS LIKELY TO REMAIN IFR THROUGH THE
  DURATION OF THE SNOW.

* TIMING OF SNOW...STARTING EARLY EVENING AND THEN PERSISTING
  UNTIL AFTER THE TAF PERIOD.

* IFR VIS WITH ONSET OF SNOW. VIS WILL LIKELY BE VARIABLE WITH
  PERIODS OF HEAVIER AND LIGHTER SNOW.

* WINDS WILL VEER FROM SWLY TO NELY THIS EVENING. NELY WINDS
  EXPECTED TO STRENGTHEN SUNDAY MORNING...WITH GUSTS TO 30KT.

KREIN

//DISCUSSION...UPDATED 12Z...

QUIET CONDITIONS WILL CONTINUE THROUGH LATE THIS AFTERNOON. A
WINTER STORM DEVELOPING OVER THE SWRN CONUS WILL TRACK
NORTHEAST...WITH PCPN OVERSPREADING THE REGION LATE THIS AFTERNOON
AND EARLY THIS EVENING. INITIALLY...TEMPERATURES SHOULD BE HIGH
ENOUGH FOR THE INITIAL PCPN TO BE RAIN OR A RAIN/SNOW MIX...BUT
TEMPERATURES WILL DROP AND PCPN SHOULD QUICKLY CHANGE OVER TO ALL
SNOW BY LATE EVENING. THIS SYSTEM IS SETTING UP TO BE LONG
DURATION EVENT WITH SNOW FALLING THROUGH LATE SUNDAY NIGHT OR INTO
EARLY MONDAY MORNING. THE PERIOD OF HEAVIEST SNOW SHOULD BE
FROM AROUND EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON
WHEN VISIBILITY MAY DROP TO BELOW 3/4SM AT TIME WITH SNOWFALL
RATES OF 1 INCH PER HOUR OR GREATER. WITH NELY WINDS RAMPING UP
THROUGH THE DAY ON SUNDAY...WITH GUSTS OF 25-30KT...BLOWING AND
DRIFTING SNOW WILL ALSO BE A CONCERN. THERE IS ALSO A CHANCE FOR
SOME LINGERING LAKE EFFECT SNOW SHOWERS ON MONDAY MORNING...BUT
THERE IS SOME UNCERTAINTY AS TO WHERE A LAKE EFFECT SNOW BAND
WOULD DEVELOP. THE LATEST GUIDANCE SUGGESTS THAT THE MAIN BAND OF
LAKE EFFECT SNOW WILL POINT INTO NWRN INDIANA...WITH GYY THE ONLY
TAF SITE IMPACTED...BUT THERE IS STILL A CHANCE FOR SOME SCT LAKE
EFFECT SNOW SHOWERS OVER NERN IL.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NONE THROUGH LATE AFTERNOON.

* CIGS LOWERING TO MVFR BY LATE AFTERNOON AND THEN TO IFR WITH
  SHORTLY AFTER SNOW ONSET. CIGS LIKELY TO REMAIN IFR THROUGH THE
  DURATION OF THE SNOW.

* TIMING OF SNOW...STARTING EARLY EVENING AND THEN PERSISTING
  UNTIL AFTER THE TAF PERIOD.

* IFR VIS WITH ONSET OF SNOW. VIS WILL LIKELY BE VARIABLE WITH
  PERIODS OF HEAVIER AND LIGHTER SNOW.

* WINDS WILL VEER FROM SWLY TO NELY THIS EVENING. NELY WINDS
  EXPECTED TO STRENGTHEN SUNDAY MORNING...WITH GUSTS TO 30KT.

KREIN

//DISCUSSION...UPDATED 12Z...

QUIET CONDITIONS WILL CONTINUE THROUGH LATE THIS AFTERNOON. A
WINTER STORM DEVELOPING OVER THE SWRN CONUS WILL TRACK
NORTHEAST...WITH PCPN OVERSPREADING THE REGION LATE THIS AFTERNOON
AND EARLY THIS EVENING. INITIALLY...TEMPERATURES SHOULD BE HIGH
ENOUGH FOR THE INITIAL PCPN TO BE RAIN OR A RAIN/SNOW MIX...BUT
TEMPERATURES WILL DROP AND PCPN SHOULD QUICKLY CHANGE OVER TO ALL
SNOW BY LATE EVENING. THIS SYSTEM IS SETTING UP TO BE LONG
DURATION EVENT WITH SNOW FALLING THROUGH LATE SUNDAY NIGHT OR INTO
EARLY MONDAY MORNING. THE PERIOD OF HEAVIEST SNOW SHOULD BE
FROM AROUND EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON
WHEN VISIBILITY MAY DROP TO BELOW 3/4SM AT TIME WITH SNOWFALL
RATES OF 1 INCH PER HOUR OR GREATER. WITH NELY WINDS RAMPING UP
THROUGH THE DAY ON SUNDAY...WITH GUSTS OF 25-30KT...BLOWING AND
DRIFTING SNOW WILL ALSO BE A CONCERN. THERE IS ALSO A CHANCE FOR
SOME LINGERING LAKE EFFECT SNOW SHOWERS ON MONDAY MORNING...BUT
THERE IS SOME UNCERTAINTY AS TO WHERE A LAKE EFFECT SNOW BAND
WOULD DEVELOP. THE LATEST GUIDANCE SUGGESTS THAT THE MAIN BAND OF
LAKE EFFECT SNOW WILL POINT INTO NWRN INDIANA...WITH GYY THE ONLY
TAF SITE IMPACTED...BUT THERE IS STILL A CHANCE FOR SOME SCT LAKE
EFFECT SNOW SHOWERS OVER NERN IL.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NONE THROUGH LATE AFTERNOON.

* CIGS LOWERING TO MVFR BY LATE AFTERNOON AND THEN TO IFR WITH
  SHORTLY AFTER SNOW ONSET. CIGS LIKELY TO REMAIN IFR THROUGH THE
  DURATION OF THE SNOW.

* TIMING OF SNOW...STARTING EARLY EVENING AND THEN PERSISTING
  UNTIL AFTER THE TAF PERIOD.

* IFR VIS WITH ONSET OF SNOW. VIS WILL LIKELY BE VARIABLE WITH
  PERIODS OF HEAVIER AND LIGHTER SNOW.

* WINDS WILL VEER FROM SWLY TO NELY THIS EVENING. NELY WINDS
  EXPECTED TO STRENGTHEN SUNDAY MORNING...WITH GUSTS TO 30KT.

KREIN

//DISCUSSION...UPDATED 12Z...

QUIET CONDITIONS WILL CONTINUE THROUGH LATE THIS AFTERNOON. A
WINTER STORM DEVELOPING OVER THE SWRN CONUS WILL TRACK
NORTHEAST...WITH PCPN OVERSPREADING THE REGION LATE THIS AFTERNOON
AND EARLY THIS EVENING. INITIALLY...TEMPERATURES SHOULD BE HIGH
ENOUGH FOR THE INITIAL PCPN TO BE RAIN OR A RAIN/SNOW MIX...BUT
TEMPERATURES WILL DROP AND PCPN SHOULD QUICKLY CHANGE OVER TO ALL
SNOW BY LATE EVENING. THIS SYSTEM IS SETTING UP TO BE LONG
DURATION EVENT WITH SNOW FALLING THROUGH LATE SUNDAY NIGHT OR INTO
EARLY MONDAY MORNING. THE PERIOD OF HEAVIEST SNOW SHOULD BE
FROM AROUND EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON
WHEN VISIBILITY MAY DROP TO BELOW 3/4SM AT TIME WITH SNOWFALL
RATES OF 1 INCH PER HOUR OR GREATER. WITH NELY WINDS RAMPING UP
THROUGH THE DAY ON SUNDAY...WITH GUSTS OF 25-30KT...BLOWING AND
DRIFTING SNOW WILL ALSO BE A CONCERN. THERE IS ALSO A CHANCE FOR
SOME LINGERING LAKE EFFECT SNOW SHOWERS ON MONDAY MORNING...BUT
THERE IS SOME UNCERTAINTY AS TO WHERE A LAKE EFFECT SNOW BAND
WOULD DEVELOP. THE LATEST GUIDANCE SUGGESTS THAT THE MAIN BAND OF
LAKE EFFECT SNOW WILL POINT INTO NWRN INDIANA...WITH GYY THE ONLY
TAF SITE IMPACTED...BUT THERE IS STILL A CHANCE FOR SOME SCT LAKE
EFFECT SNOW SHOWERS OVER NERN IL.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 311152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NONE THROUGH LATE AFTERNOON.

* CIGS LOWERING TO MVFR BY LATE AFTERNOON AND THEN TO IFR WITH
  SHORTLY AFTER SNOW ONSET. CIGS LIKELY TO REMAIN IFR THROUGH THE
  DURATION OF THE SNOW.

* TIMING OF SNOW...STARTING EARLY EVENING AND THEN PERSISTING
  UNTIL AFTER THE TAF PERIOD.

* IFR VIS WITH ONSET OF SNOW. VIS WILL LIKELY BE VARIABLE WITH
  PERIODS OF HEAVIER AND LIGHTER SNOW.

* WINDS WILL VEER FROM SWLY TO NELY THIS EVENING. NELY WINDS
  EXPECTED TO STRENGTHEN SUNDAY MORNING...WITH GUSTS TO 30KT.

KREIN

//DISCUSSION...UPDATED 12Z...

QUIET CONDITIONS WILL CONTINUE THROUGH LATE THIS AFTERNOON. A
WINTER STORM DEVELOPING OVER THE SWRN CONUS WILL TRACK
NORTHEAST...WITH PCPN OVERSPREADING THE REGION LATE THIS AFTERNOON
AND EARLY THIS EVENING. INITIALLY...TEMPERATURES SHOULD BE HIGH
ENOUGH FOR THE INITIAL PCPN TO BE RAIN OR A RAIN/SNOW MIX...BUT
TEMPERATURES WILL DROP AND PCPN SHOULD QUICKLY CHANGE OVER TO ALL
SNOW BY LATE EVENING. THIS SYSTEM IS SETTING UP TO BE LONG
DURATION EVENT WITH SNOW FALLING THROUGH LATE SUNDAY NIGHT OR INTO
EARLY MONDAY MORNING. THE PERIOD OF HEAVIEST SNOW SHOULD BE
FROM AROUND EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON
WHEN VISIBILITY MAY DROP TO BELOW 3/4SM AT TIME WITH SNOWFALL
RATES OF 1 INCH PER HOUR OR GREATER. WITH NELY WINDS RAMPING UP
THROUGH THE DAY ON SUNDAY...WITH GUSTS OF 25-30KT...BLOWING AND
DRIFTING SNOW WILL ALSO BE A CONCERN. THERE IS ALSO A CHANCE FOR
SOME LINGERING LAKE EFFECT SNOW SHOWERS ON MONDAY MORNING...BUT
THERE IS SOME UNCERTAINTY AS TO WHERE A LAKE EFFECT SNOW BAND
WOULD DEVELOP. THE LATEST GUIDANCE SUGGESTS THAT THE MAIN BAND OF
LAKE EFFECT SNOW WILL POINT INTO NWRN INDIANA...WITH GYY THE ONLY
TAF SITE IMPACTED...BUT THERE IS STILL A CHANCE FOR SOME SCT LAKE
EFFECT SNOW SHOWERS OVER NERN IL.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 311129
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
529 AM CST Sat Jan 31 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT JAN 31 2015

Quiet weather is expected to start the day across central and
southeast Illinois. A ridge of high pressure, currently paralleling
the Ohio River Valley, will continue to pull away from the area.
This will allow a storm system, starting to get organized over the
southwest United States, to approach. Decent WAA/isentropic lift
ahead of the approaching storm will result in steadily
increasing/thickening cloud cover this morning. Rain will begin to
spread across the forecast area from southwest to northeast this
afternoon. A rain/snow mix can`t be ruled out by late afternoon
across our far northwest counties, mainly Knox, Stark, and Marshall,
but no snow accumulation is anticipated before tonight. The
southerly winds will push temperatures above normal, despite the
cloud cover and precipitation breaking out, with highs near 40
degrees in most areas.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT JAN 31 2015

Surface wave moving out of the desert SW and phasing with an upper
level trof in the more northern portion of the 500mb flow over the
CONUS to bring the next winter storm for the Midwest Saturday and
Sunday.  Models continue to track a little further north with the
solutions...putting more and more warm air ahead of the low.  This
warmer trend ahead of the system will keep the precipitation mainly
rain even into the evening hours.  Cold air is not as deep and
abundant with this system, and the strong southerly flow in advance
of the sfc low keeping the low levels warm enough for rain.  NAM
Bufkit soundings not switching over to all snow for PIA until
between 03-06z.  However, have rain/snow mix for the evening, but
temps very at or above freezing through most of the evening up to
midnight will limit the accumulations and/or make for a very slushy
wet mix.  Once the low draws closer and more cold air is pulled into
the system, the changeover to snow will become more widespread
across the area, mainly north of the I-70 corridor.  Areas between
I-70 and roughly I-72 will see a mix a bit longer as well, but still
changing over to mostly snow by Sunday.  Snow lingering into Sunday
evening before ending by Monday morning.

Significant accumulations are expected with this storm...over an
extended period of time.  Winter Storm Warning is confined to a
Rushville to Bloomington line. Traditional Winter Storm Warning
criteria will be very close...though 6"-8" are expected in the
warned area in TOTAL...the snow will accumulate over an extended
period of time-18 to 24 hours-- with the best snowfall accumulations
expected between early Sunday morning and Sunday evening.  The
Winter Weather Advisory south of the warning up to, but not
including, the I-70 corridor will also see the accumulations over a
longer duration event.  Although the southeast likely to see mostly
rain, some snow accumulations will drop south of I-70 by Monday
morning as well.

Phasing of this sfc system with an open wave aloft resulting in
weaker dynamics in the bigger picture and a slower deepening of the
low.  Lift at any given time good to moderate, but limited by lack
of deeper organization. Isentropic lift definitely there on 305-320K
sfcs, but never for long and angle of winds to gradient closer to 45
than to perpendicular. Models struggling with over deepening of the
system and potentially with the snowfall accumulations being
overdone somewhat with the warmer air moving into the system.  That
being said...even reducing the snowfall totals from model qpf...over
such a long duration with a slow moving system, the totals are still
in warning/advisory criteria for much of the Midwest.

Winds increasing as the storm moves through, particularly on Sunday
afternoon could result in some blowing snow over the northern tier
of ILX, although the snow will initially be more wet and heavy...as
the storm goes on the SLRs will increase and snow be more prone to
blowing and drifting.

Cold air moving in behind the system will result in a very chilly
Monday and another quick wave Monday will bring another chance for
some snow mainly across the northern third of the state.
Accumulations are expected to be low at this point with that
system.  Beyond that, the forecast is relatively quiet through the
work week with moderate temperatures until deeper cold air moves
into the region dropping high temps at the end of the week into the
teens and 20s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 520 AM CST SAT JAN 31 2015

Condtions across the central Illinois terminals will start out
quiet/VFR as departing high pressure slowly loses its grip on the
area. This will allow a rapid thickening/lowering of the clouds as
a storm system approaches from the west. Rain will begin to break
out from these thicker clouds later this afternoon, with light
rain expected to develop as well. The persistent precipitation
will eventually see conditions degrade to IFR this evening. The
precipitation will also gradually mix with and change over to snow
as cooler air begins to filter into the area.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>043-047-048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ044>046-049>057-061.

&&

$$

SHORT TERM...Bak
LONG TERM...HJS
AVIATION...Bak







000
FXUS63 KILX 311129
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
529 AM CST Sat Jan 31 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT JAN 31 2015

Quiet weather is expected to start the day across central and
southeast Illinois. A ridge of high pressure, currently paralleling
the Ohio River Valley, will continue to pull away from the area.
This will allow a storm system, starting to get organized over the
southwest United States, to approach. Decent WAA/isentropic lift
ahead of the approaching storm will result in steadily
increasing/thickening cloud cover this morning. Rain will begin to
spread across the forecast area from southwest to northeast this
afternoon. A rain/snow mix can`t be ruled out by late afternoon
across our far northwest counties, mainly Knox, Stark, and Marshall,
but no snow accumulation is anticipated before tonight. The
southerly winds will push temperatures above normal, despite the
cloud cover and precipitation breaking out, with highs near 40
degrees in most areas.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT JAN 31 2015

Surface wave moving out of the desert SW and phasing with an upper
level trof in the more northern portion of the 500mb flow over the
CONUS to bring the next winter storm for the Midwest Saturday and
Sunday.  Models continue to track a little further north with the
solutions...putting more and more warm air ahead of the low.  This
warmer trend ahead of the system will keep the precipitation mainly
rain even into the evening hours.  Cold air is not as deep and
abundant with this system, and the strong southerly flow in advance
of the sfc low keeping the low levels warm enough for rain.  NAM
Bufkit soundings not switching over to all snow for PIA until
between 03-06z.  However, have rain/snow mix for the evening, but
temps very at or above freezing through most of the evening up to
midnight will limit the accumulations and/or make for a very slushy
wet mix.  Once the low draws closer and more cold air is pulled into
the system, the changeover to snow will become more widespread
across the area, mainly north of the I-70 corridor.  Areas between
I-70 and roughly I-72 will see a mix a bit longer as well, but still
changing over to mostly snow by Sunday.  Snow lingering into Sunday
evening before ending by Monday morning.

Significant accumulations are expected with this storm...over an
extended period of time.  Winter Storm Warning is confined to a
Rushville to Bloomington line. Traditional Winter Storm Warning
criteria will be very close...though 6"-8" are expected in the
warned area in TOTAL...the snow will accumulate over an extended
period of time-18 to 24 hours-- with the best snowfall accumulations
expected between early Sunday morning and Sunday evening.  The
Winter Weather Advisory south of the warning up to, but not
including, the I-70 corridor will also see the accumulations over a
longer duration event.  Although the southeast likely to see mostly
rain, some snow accumulations will drop south of I-70 by Monday
morning as well.

Phasing of this sfc system with an open wave aloft resulting in
weaker dynamics in the bigger picture and a slower deepening of the
low.  Lift at any given time good to moderate, but limited by lack
of deeper organization. Isentropic lift definitely there on 305-320K
sfcs, but never for long and angle of winds to gradient closer to 45
than to perpendicular. Models struggling with over deepening of the
system and potentially with the snowfall accumulations being
overdone somewhat with the warmer air moving into the system.  That
being said...even reducing the snowfall totals from model qpf...over
such a long duration with a slow moving system, the totals are still
in warning/advisory criteria for much of the Midwest.

Winds increasing as the storm moves through, particularly on Sunday
afternoon could result in some blowing snow over the northern tier
of ILX, although the snow will initially be more wet and heavy...as
the storm goes on the SLRs will increase and snow be more prone to
blowing and drifting.

Cold air moving in behind the system will result in a very chilly
Monday and another quick wave Monday will bring another chance for
some snow mainly across the northern third of the state.
Accumulations are expected to be low at this point with that
system.  Beyond that, the forecast is relatively quiet through the
work week with moderate temperatures until deeper cold air moves
into the region dropping high temps at the end of the week into the
teens and 20s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 520 AM CST SAT JAN 31 2015

Condtions across the central Illinois terminals will start out
quiet/VFR as departing high pressure slowly loses its grip on the
area. This will allow a rapid thickening/lowering of the clouds as
a storm system approaches from the west. Rain will begin to break
out from these thicker clouds later this afternoon, with light
rain expected to develop as well. The persistent precipitation
will eventually see conditions degrade to IFR this evening. The
precipitation will also gradually mix with and change over to snow
as cooler air begins to filter into the area.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>043-047-048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ044>046-049>057-061.

&&

$$

SHORT TERM...Bak
LONG TERM...HJS
AVIATION...Bak






000
FXUS63 KLOT 311003 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
403 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT.
  INTENSITY MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT
  PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

KREIN

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 311003 AAA
AFDLOT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
403 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

LAKESHORE FLOOD THREAT...
STRONG NORTHEAST WINDS UP TO GALE FORCE WILL LIKELY RESULT IN
LARGE AND BATTERING WAVES DEVELOPING ALONG THE ILLINOIS AND
INDIANA SHORES SUNDAY AFTERNOON AND EVENING. LAKE LEVELS REMAIN
NEARLY A FOOT AND A HALF ABOVE NORMAL...THOUGH DOWN A BIT FROM
WHERE THEY WERE DURING THE HALLOWEEN STORM. ALONG THE LAKEFRONT
FRIDAY AFTERNOON I SAW A LOT OF FRAZZLE ICE HAD DEVELOPED WHICH
COULD HAVE THE EFFECT TO DAMPEN WAVES A BIT ALONG THE SHORE. NONE-
THE-LESS SOME MINOR LAKESHORE FLOODING IS POSSIBLE IF WAVES BUILD
UP TO 10 TO 14 FT AS FORECAST...THOUGH IMPACTS WILL LIKELY BE
PRETTY TRIVIAL SO NOT PLANNING ANY LAKESHORE FLOOD HEADLINES AT
THIS TIME. NOT OUT OF THE QUESTION THAT WE MAY NEED A LAKESHORE
FLOOD ADVISORY EVENTUALLY...PARTICULARLY IF WIND/WAVE FORECAST
GOES ANY HIGHER.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT.
  INTENSITY MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT
  PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

KREIN

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
348 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT.
  INTENSITY MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT
  PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

KREIN

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
348 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT.
  INTENSITY MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT
  PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

KREIN

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
348 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT.
  INTENSITY MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT
  PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

KREIN

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
348 AM CST SAT JAN 31 2015

.SHORT TERM...
348 AM CST

THROUGH SUNDAY NIGHT...

SIGNIFICANT WINTER STORM STILL POISED TO AFFECT THE AREA STARTING
TONIGHT AND CONTINUING THROUGH SUNDAY EVENING.

HEADLINES...
HAVE GONE AHEAD AND UPGRADED THE ENTIRE CWA TO A WINTER STORM
WARNING FOR LATE THIS EVENING THROUGH SUNDAY EVENING. FOR SIMPLICITY
SAKE...HAVE GONE WITH SAME START AND END TIME ACROSS THE CWA...AN
ARGUMENT COULD HAVE BEEN MADE TO START LATER IN SOUTHERN CWA AND
AREAS NEAR THE LAKE COULD NEED TO BE EXTENDED A BIT IF LAKE EFFECT
IS MORE IMPRESSIVE THAN EXPECTED...BUT GENERALLY THINK THAT 03Z THIS
EVENING THROUGH 03Z SUNDAY EVENING WILL COVER THE MEAT AND POTATOES
OF THE EVENT MOST AREAS.

SYNOPTICS/MODELS ANALYSIS...
STILL LOOKING A FAIRLY COMPLEX EVOLUTION OF PATTERN THE NEXT COUPLE
OF DAYS AS VIGOROUS SHORTWAVE OVER ALBERTA IS FORECAST TO DIG
SOUTHEAST INTO THE NORTHERN AND CENTRAL ROCKIES AS STRONG CLOSED LOW
OVER THE SOUTHWEST DROPS SOUTH AND BECOMES INCREASINGLY CUT OFF FROM
BELT OF WESTERLIES. FARTHER NORTH A STRONG SHORTWAVE PIVOTING AROUND
HUDSON LOW WILL HELP DRIVE A COLD FRONT SOUTH INTO NORTHERN ILLINOIS
THIS EVENING WITH THE FRONT STALLING OUT. AS STRONG ALBERTA CLIPPER
DROPS SOUTH INTO THE ROCKIES LOOK FOR CYCLOGENESIS TO OCCUR OVER
COLORADO TODAY...THEN TRACK EAST TOWARD THE OHIO VALLEY AND
STRENGTHEN TONIGHT AND SUNDAY AS 500MB SHORTWAVE IS FORECAST TO
AMPLIFY AS IT TRACKS EAST.

THE SPREAD IN THE MODELS BETWEEN THE NAM/GFS/ECMWF HAS DECREASED
THROUGH SUNDAY NIGHT...WHICH DOES LEND TO SOME UPTICK IN CONFIDENCE.
HOWEVER...IT IS STILL A COMPLEX INTERACTION OF SEVERAL KEY FEATURES
FORECAST TO TAKE PLACE AND NUMERICAL WEATHER GUIDANCE HAS HUNG US
OUT TO DRY REPEATEDLY THIS WINTER...MAKING IT HARD TO GO RUNNING
BACK INTO ITS OPEN ARMS AND TRUSTING IT. STILL...GIVEN THE
DECREASING SPREAD IN THE MODELS THROUGH SUNDAY NIGHT IT IS A BIT
EASIER TO DEVELOP SOME MORE CONFIDENCE IN THE FORECAST EVOLUTION OF
THIS SYSTEM.

NITTY GRITTY DETAILS...
BROAD AND STRENGTHENING WARM AIR ADVECTION REGIME IS LIKELY TO
RESULT IN AN EXPANDING SHIELD OF PRECIPITATION FROM THE LOWER
MISSOURI VALLEY THIS MORNING EASTWARD INTO OUR AREA LATE THIS
AFTERNOON AND EARLY THIS EVENING. INITIALLY IT WOULD APPEAR AS
THOUGH TEMPERATURES TODAY WILL BE WARM ENOUGH FOR PRECIPITATION TO
BE ALL RAIN. WEAK FRONT IS FORECAST TO BASICALLY BISECT THE CWA AT
00Z THIS EVENING AND ONLY SLOWLY SAG SOUTH THROUGH THE NIGHT. TO THE
SOUTH OF THE WEAK FRONT LOOK FOR SOUTHERLY WINDS AND CONTINUED WARM
AIR ADVECTION TO HOLD TEMPERATURES NEAR OR PERHAPS JUST ABOVE
FREEZING SOUTH OF I-80 EARLY THIS EVENING AND PERHAPS INTO THE LATE
EVENING SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS. AM CONCERNED
BECAUSE A VERY COMMON BIAS IN MODEL GUIDANCE IS TO UNDERESTIMATE THE
IMPACTS OF WARM AIR ADVECTION ON P-TYPE IN DEVELOPING CYCLONES LIKE
THIS...WHICH IF ALL THE MASS FIELDS VERIFY PERFECTLY HAS ME
CONCERNED THAT PRECIP COULD BE RAIN OR HAVE RAIN MIXED IN WELL INTO
THE EVENING HOURS INTO SOUTHERN AND POSSIBLY EVEN CENTRAL PORTIONS
OF THE CWA. GIVEN THIS CONCERN HAVE GREATLY REDUCED SNOW ACCUMS THIS
EVENING...ESPECIALLY SOUTH OF I-80 AND EVEN LOWERED RATIOS INTO
SUNDAY MORNING WHERE FORECAST MODEL 2M TEMPS NEAR 32F MAKE ME VERY
LEARY OF SEEING BIG ACCUMULATIONS OCCUR. THE AREAS SOUTH OF
KANKAKEE/ILLINOIS RIVERS SEEM TO STAND THE HIGHEST CHANCE OF A
FORECAST BUST AND IF THE ACCUMULATING SNOW STARTS LATE ENOUGH COULD
EASILY END UP BELOW 5 INCHES FOR THE 24 HOURS PERIOD.

CONFIDENCE IS LOW WHEN PRECIP WILL TURN TO ALL SNOW FAR SOUTH THOUGH
SREF GUIDANCE SUGGESTS BY 06Z...WORRIED THIS COULD BE DELAYED IF THE
TYPICAL MODEL BIAS OF UNDERESTIMATING WAA MAGNITUDE PLAYS OUT.
EVENTUALLY IT WILL TURN TO ALL SNOW AND SHOULD BEGIN TO ACCUMULATE
IF NOT LATE TONIGHT THEN CERTAINLY DURING THE DAY ON SUNDAY AS TEMPS
BEGIN TO PLUMMET. PRECIP LOOKS MORE LIKELY TO BE ALL SNOW NORTH OF
I-88/290...THOUGH THERMAL FIELDS AND FORECAST OMEGA VALUES DO NOT
SUPPORT HIGH SNOW:LIQUID RATIOS FOR THE MAJORITY OF THE EVENT. BY
SUNDAY AFTERNOON AS WE TRANSITION INTO THE DEFORMATION ZONE AND
COLUMN COOLS WILL LIKELY SEE A GRADUAL TRANSITION TO DRIER/HIGHER
RATIO SNOWS.

MODEL QPF REMAINS VERY IMPRESSIVE WITH MAJORITY OF MODELS LAYING OUT
A SWATH OF LIQUID EQUIVS OF 1" OR GREATER OVER PORTIONS OF OUR CWA.
SYSTEM WILL BEGIN TO TAP INTO THE HIGHER PWAT AIR MASS OVER THE GULF
OF MEXICO AND GFS/NAM AGREE THAT PWATS WILL CLIMB TO OVER 0.5" INTO
OUR CWA WHICH IS IN THE 90TH PERCENTILE OF PWATS FOR THIS TIME OF
YEAR. MODELS REALLY NEVER SHOW ANY INTENSE/STRONG ASCENT...BUT
RATHER A LONG DURATION OF MODEST ASCENT WHICH GIVEN THE ACCOMPANYING
UNSEASONABLY MOIST AIR MASS COULD CERTAINLY SUPPORT FORECAST QPF
VALUES. THE MILLION DOLLAR QUESTION IS HOW MUCH OF THE PRECIP WILL
FALL AS ALL SNOW AND HOW LONG WILL IT TAKE IT TO START ACCUMULATING.
THE FARTHER NORTH YOU GO INTO THE CWA THE LESSER THE CHANCE AND
SHORTER THE DURATION OF ANY MIXED SLEET OR RAIN AND THE SOONER SNOW
WILL ACCUMULATE. THIS AREA IS WHERE THE SLIGHTLY LESSER QPF VALUES
ARE...WHILE FARTHER SOUTH WITHIN THE SWATH OF FORECAST QPF >1 INCH
THERE ARE BIG QUESTIONS ABOUT DURATION OF ANY MIXED RAIN AND HOW
SOON AFTER THE TRANSITION TO SNOW THAT IT WILL START TO ACCUMULATE.
IF PRECIP STARTS AS RAIN AND TURNS TO SNOW WITH TEMPS OF 32F OR 33F
THEN IT COULD SNOW FOR A WHILE BEFORE ACCUMULATING...AND FOR THIS
REASON HAS SHOWN AT LEAST A THIRD OF AN INCH OF THE QPF FALLING AS
RAIN OR NON-ACCUMULATING SNOW.

GIVEN THE CURRENT FORECAST TRACK THE AXIS OF HEAVIEST SNOW LOOKS TO
LAY OUT SOMEWHERE IN THE I-80 OR I-88/290 CORRIDOR WHERE ACCUMS
COULD POTENTIALLY PUSH DOUBLE DIGITS BY THE TIME IT IS ALL SAID AND
DONE SUNDAY EVENING. EVEN OUTSIDE THIS SWATH SIGNIFICANT
ACCUMULATIONS OF 5-8 INCHES LOOK PRETTY LIKELY. STRENGTHENING
NORTHEAST WINDS AND COMBINED WITH GRADUALLY DECREASING SNOW DENSITY
SHOULD ALLOW FOR SOME BLOWING AND DRIFTING SNOW TO DEVELOP SUNDAY
AFTERNOON AND CONTINUED INTO SUNDAY EVENING...ESPECIALLY NORTHERN
CWA WHERE SNOW SHOULD BE LIGHTEST AND MOST BLOWABLE.

LAKE ENHANCEMENT/LAKE EFFECT...
AS DEPTH OF THE COLD AIR MASS BEGINS TO INCREASE SUNDAY AFTERNOON
AND EVENING LOOK FOR THE POTENTIAL FOR INITIALLY SOME LAKE
ENHANCEMENT PROBABLY TRANSITIONING TO PURE LAKE EFFECT SUNDAY NIGHT
AS SYSTEM SNOWS MOVE OUT. OVERALL THE LAKE EFFECT SET-UP APPEARS
MARGINAL AND DESPITE THE STRONG CONVERGENCE/LOW LEVEL ASCENT
INDICATED IN THE HIGH-RES MODELS SUSPECT THE LAKE CONTRIBUTIONS TO
THE SNOWFALL WILL NOT BE TERRIBLY SIGNIFICANT. INVERSION HEIGHTS
NEAR OR BELOW 5000FT SUGGEST CONVECTION WILL BE SHALLOW AND DESPITE
FAVORABLE TEMPS BELOW THE INVERSION FOR SNOW GROWTH...THE DEPTH OF
THE CONVECTION LOOKS TOO SHALLOW TO SUPPORT MUCH MORE THAN LIGHT
LAKE EFFECT SNOW SHOWERS. THE LOW LEVEL INSTABILITY IS ALSO PROGGED
TO BE WEAK WITH ONLY A COUPLE HUNDRED JOULES OF LAKE INDUCED CAPE
BELOW THE INVERSION. GIVEN THE CURRENT FORECAST THERMODYNAMICS
THINKING THAT THE LAKE CONTRIBUTIONS TO SNOWFALL TOTALS WILL BE
MINIMAL BUT PROBABLY ENOUGH TO KEEP LIGHT SNOW SHOWERS GOING SO HAVE
MAINTAINED THE HIGH POPS NEAR THE LAKE SUNDAY NIGHT.

IZZI

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT.
  INTENSITY MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT
  PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

KREIN

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 310931
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
331 AM CST Sat Jan 31 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT JAN 31 2015

Quiet weather is expected to start the day across central and
southeast Illinois. A ridge of high pressure, currently paralleling
the Ohio River Valley, will continue to pull away from the area.
This will allow a storm system, starting to get organized over the
southwest United States, to approach. Decent WAA/isentropic lift
ahead of the approaching storm will result in steadily
increasing/thickening cloud cover this morning. Rain will begin to
spread across the forecast area from southwest to northeast this
afternoon. A rain/snow mix can`t be ruled out by late afternoon
across our far northwest counties, mainly Knox, Stark, and Marshall,
but no snow accumulation is anticipated before tonight. The
southerly winds will push temperatures above normal, despite the
cloud cover and precipitation breaking out, with highs near 40
degrees in most areas.


&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT JAN 31 2015

Surface wave moving out of the desert SW and phasing with an upper
level trof in the more northern portion of the 500mb flow over the
CONUS to bring the next winter storm for the Midwest Saturday and
Sunday.  Models continue to track a little further north with the
solutions...putting more and more warm air ahead of the low.  This
warmer trend ahead of the system will keep the precipitation mainly
rain even into the evening hours.  Cold air is not as deep and
abundant with this system, and the strong southerly flow in advance
of the sfc low keeping the low levels warm enough for rain.  NAM
Bufkit soundings not switching over to all snow for PIA until
between 03-06z.  However, have rain/snow mix for the evening, but
temps very at or above freezing through most of the evening up to
midnight will limit the accumulations and/or make for a very slushy
wet mix.  Once the low draws closer and more cold air is pulled into
the system, the changeover to snow will become more widespread
across the area, mainly north of the I-70 corridor.  Areas between
I-70 and roughly I-72 will see a mix a bit longer as well, but still
changing over to mostly snow by Sunday.  Snow lingering into Sunday
evening before ending by Monday morning.

Significant accumulations are expected with this storm...over an
extended period of time.  Winter Storm Warning is confined to a
Rushville to Bloomington line. Traditional Winter Storm Warning
criteria will be very close...though 6"-8" are expected in the
warned area in TOTAL...the snow will accumulate over an extended
period of time-18 to 24 hours-- with the best snowfall accumulations
expected between early Sunday morning and Sunday evening.  The
Winter Weather Advisory south of the warning up to, but not
including, the I-70 corridor will also see the accumulations over a
longer duration event.  Although the southeast likely to see mostly
rain, some snow accumulations will drop south of I-70 by Monday
morning as well.

Phasing of this sfc system with an open wave aloft resulting in
weaker dynamics in the bigger picture and a slower deepening of the
low.  Lift at any given time good to moderate, but limited by lack
of deeper organization. Isentropic lift definitely there on 305-320K
sfcs, but never for long and angle of winds to gradient closer to 45
than to perpendicular. Models struggling with over deepening of the
system and potentially with the snowfall accumulations being
overdone somewhat with the warmer air moving into the system.  That
being said...even reducing the snowfall totals from model qpf...over
such a long duration with a slow moving system, the totals are still
in warning/advisory criteria for much of the Midwest.

Winds increasing as the storm moves through, particularly on Sunday
afternoon could result in some blowing snow over the northern tier
of ILX, although the snow will initially be more wet and heavy...as
the storm goes on the SLRs will increase and snow be more prone to
blowing and drifting.

Cold air moving in behind the system will result in a very chilly
Monday and another quick wave Monday will bring another chance for
some snow mainly across the northern third of the state.
Accumulations are expected to be low at this point with that
system.  Beyond that, the forecast is relatively quiet through the
work week with moderate temperatures until deeper cold air moves
into the region dropping high temps at the end of the week into the
teens and 20s.


&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1143 PM CST FRI JAN 30 2015

VFR conditions will prevail through Saturday morning as high
pressure gradually shifts east of the region. Clouds will begin to
thicken/lower by afternoon in advance of an approaching storm
system. All model guidance brings light rain into the area between
19z and 21z, with forecast soundings suggesting ceilings lowering
into the MVFR category at that time. As profiles moisten/cool
further, a rain/snow mix will develop at the terminals prior to
06z.  Have reduced visbys and lowered ceilings to IFR accordingly.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 9 PM this evening to 9 PM CST Sunday
FOR ILZ027>031-036>038-040>043-047-048.

WINTER WEATHER ADVISORY from 9 PM this evening to 9 PM CST
Sunday FOR ILZ044>046-049>057-061.

&&

$$

SHORT TERM...Bak
LONG TERM...HJS
AVIATION...Barnes







000
FXUS63 KLOT 310845
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
245 AM CST SAT JAN 31 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT.
  INTENSITY MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT
  PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

KREIN

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
243 AM CST

DISCUSSION...INCREASING NORTHEAST WINDS TONIGHT AND SUNDAY...LIKELY
REACHING GALE FORCE ACROSS SOUTHERN LAKE MICHIGAN WILL BE THE FOCUS
OF THE FORECAST. HIGH PRESSURE IS SPREAD FROM THE LOWER LAKES ACROSS
THE OHIO VALLEY AND TO THE GULF COAST THIS MORNING. WEST TO
SOUTHWEST WINDS HAVE SET UP ACROSS THE LAKE BEHIND THE HIGH. ONE AREA
OF LOW PRESSURE MOVING ACROSS NORTHERN ONTARIO WILL BRING A TROUGH
ACROSS THE LAKE INTO THE AFTERNOON TURNING WINDS NORTHWESTERLY THEN
NORTHEASTERLY LATE AS A NEW LOW DEVELOPS ACROSS THE FRONT RANGE OF
THE ROCKIES...WHICH THEN DEEPENS ACROSS KANSAS AND MISSOURI. SPEEDS
WILL STEADILY INCREASE TONIGHT AND PEAK SUNDAY AS THE LOW TRACKS
INTO CENTRAL INDIANA. WINDS WILL THEN TURN NORTHERLY SUNDAY EVENING
AS THE LOW TRACKS TO THE EAST AND HIGH PRESSURE APPROACHES FROM THE
WEST. STEADY 25-30 KT WINDS ARE LIKELY BY SUNDAY AFTERNOON WITH
GUSTS TO GALE FORCE AROUND 35 KT. THE SYSTEM HAS SHOWED A STRONGER
TREND NOW THAT THE FEATURES DRIVING IT ARE COMING TOGETHER SO 40 KT
IS NOT OUT OF THE QUESTION. WILL CONTINUE WITH THE GALE WATCH FOR
SOUTHERN LAKE MICHIGAN AND THE NEARSHORE WATERS. SOME ICE HAS FORMED
ALONG THE SHORELINE FRIDAY BUT IT LIKELY THIN AND MAY BREAK UP TODAY
THANKS TO MILDER TEMPS AND SOME SUN EARLY. IF NOTHING ELSE
INCREASING WINDS WILL LIKELY BREAK IT UP SO THERE MAY BE LITTLE
TEMPERING AFFECT ON THE WAVES AS A RESULT.

WINDS SLACKEN INTO MONDAY MORNING WITH HIGH PRESSURE PASSING SOUTH
OF THE LAKE LATER IN THE DAY. ANOTHER LOW. SEVERAL LOWS CROSS THE
REGION TUESDAY AND WEDNESDAY BRINGING A PERIOD OF MODEST SOUTHWEST
WINDS BUT A SHIFT TO NORTHWEST WILL OCCUR WEDNESDAY WITH STRONG HIGH
PRESSURE SPREADING IN WEDNESDAY NIGHT.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
     ILZ023-ILZ032-ILZ033-ILZ039...9 PM SATURDAY TO 9 PM SUNDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 9 PM SUNDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310800
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
200 AM CST SAT JAN 31 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT. INTENSITY
  MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

MDB

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310800
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
200 AM CST SAT JAN 31 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
200 AM CST

MONDAY THROUGH FRIDAY...

BY MONDAY MORNING...THE SYSTEM THAT IS EXPECTED TO BRING THE WEEKEND
SNOWFALL SHOULD SHIFT WELL TO THE EAST...WITH THE SFC LOW MOVING TO
THE MID ATLANTIC REGION WHILE HIGH PRESSURE BUILDS JUST WEST OF THE
MISSISSIPPI RIVER.  THE RESULTANT LONG...NORTHERLY FETCH OVER LAKE
MICHIGAN SHOULD BE CONDUCIVE TO A LAKE EFFECT BAND OF SNOW
DEVELOPING ALONG THE SPINE OF THE LAKE...AND THE SFC WIND FIELD
ADVERTISED BY MUCH OF THE GUIDANCE DOES INDICATE A SFC CONVERGENCE
BAND AS WELL.  SO...WOULD EXPECT A BAND OF LAKE EFFECT SNOW SHOWERS
POINTING INTO NWRN INDIANA MONDAY MORNING.  THE OVERALL PATTERN
SHOULD BE FAIRLY PROGRESSIVE...SO DO NOT ANTICIPATE THAT A BAND
WOULD SET UP OVER A SINGLE AREA FOR VERY LONG...WITH THE LAKE EFFECT
BAND GRADUALLY MOVING EAST THROUGH THE DAY...PERHAPS JUST CLIPPING
NERN PORTER COUNTY IN THE AFTERNOON.  FOLLOWING THE SYNOPTIC
SNOW...DO NOT ANTICIPATE THAT THIS LAKE EFFECT BAND WOULD
SIGNIFICANTLY ADD TO THE PREVIOUS SNOWFALL.  AS THE SFC HIGH
PRESSURE BUILDS EWD THROUGH THE DAY...TEMPERATURES ACROSS THE REGION
WILL LIKELY ONLY SEE A 5 TO 10 DEGREE DIURNAL RISE THROUGH THE DAY
WITH HIGHS ONLY IN THE TEENS.  BY TUESDAY...THE UPPER LEVEL PATTERN
IS EXPECTED TO BECOME MUCH MORE ZONAL...WITH A SERIES OF WEAK
SHORTWAVES RIPPLING THROUGH THE FAST UPPER LEVEL FLOW.  TIMING OF
INDIVIDUAL SHORTWAVES IN FAST ZONAL FLOW ALOFT BECOMES MORE
PROBLEMATIC WITH TIME...SO CONFIDENCE IN THE EXACT TIMING OF ANY
INDIVIDUAL SYSTEM IMPACTING THE REGION WOULD BE MODERATE AT BEST.
HOWEVER...THAT BEING SAID...THE NEXT CHANCE FOR PCPN ACROSS THE AREA
SHOULD BE MONDAY NIGHT INTO TUESDAY MORNING AS A WEAK
PACIFIC-SOURCED SHORTWAVE QUICKLY SCOOT ACROSS THE AREA...POSSIBLY
BRINGING A LITTLE LIGHT SNOW.  WITH HIGH PRESSURE EXTENDING FROM THE
UPPER OHIO VALLEY THROUGH EAST TEXAS...THERE WILL LITTLE MOISTURE
TRANSPORT FROM THE GLFMEX AND ANY ACCUMULATIONS ASSOCIATED WITH THIS
SYSTEM SHOULD BE LIGHT.  ANOTHER PACIFIC SHORTWAVE...QUICK ON THE
HEELS OF THE FIRST ONE MAY BRING SOME MORE LIGHT SNOW FOR TUESDAY
NIGHT INTO WEDNESDAY...BUT AGAIN...ANY ACCUMULATIONS SHOULD BE
LIGHT.  BY WEDNESDAY NIGHT...ARCTIC HIGH PRESSURE BUILDING OUT OF
CANADA SHOULD SPREAD ACROSS THE NRN PLAINS AND ACROSS THE GREAT
LAKES REGION BY THURSDAY MORNING.  THIS WILL BRING MUCH COLDER
AIR...WITH LOWS DROPPING BELOW 0F OVER THE NWRN PORTIONS OF THE CWA
THURSDAY MORNING...WITH THE REMAINDER OF THE AREA DROPPING INTO THE
SINGLE DIGITS ABOVE 0F. THE COLD...ARCTIC HIGH PRESSURE WILL
DOMINATE THE REGION FOR THE REMAINDER OF THE WEEK.  THE COLDEST
PERIOD SHOULD BE THURSDAY NIGHT INTO FRIDAY MORNING TEMPERATURES
BELOW 0F OVER MUCH OF THE AREA AWAY FROM THE IMMEDIATE
LAKEFRONT...AND EVEN THERE...TEMPERATURES SHOULD ONLY BE IN THE
LOWER SINGLE DIGITS ABOVE ZERO.  THERE SHOULD BE A LITTLE MODERATION
TO TEMPERATURES BY FRIDAY AS THE CENTER OF THE HIGH SLIDES TO THE
EAST AND LOW LEVEL FLOW BECOMES MORE SOUTHERLY...DRAWING SOME
SLIGHTLY WARMER AIR INTO THE REGION WITH HIGHS ON FRIDAY IN THE
UPPER TEENS TO LOWER 20S.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT. INTENSITY
  MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

MDB

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 310547
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1147 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT. INTENSITY
  MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

MDB

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310547
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1147 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE THROUGH MID AFTERNOON.

* CIGS LOWERING TO MVFR LATE AFTERNOON THEN IFR BY LATE EVENING OR
  EARLY OVERNIGHT IN SNOW.

* SNOW SPREADS IN EARLY/MID EVENING CONTINUING THROUGH THE NIGHT. INTENSITY
  MAY WANE AT TIMES DURING THE EARLY OVERNIGHT...BUT PICK UP LATE.

* IFR VSBY EXPECTED IN SNOW BUT MAY SEE SOME INTERMITTENT
  IMPROVEMENT DURING THE EARLY OVERNIGHT HOURS.

* WINDS TURN FROM SOUTHWEST TO NORTHEAST EARLY/MID EVENING. MAY BE
  A PERIOD OF VARIABLE WINDS AROUND/JUST AFTER SUNSET. SPEEDS
  INCREASE EARLY SUNDAY MORNING.

MDB

//DISCUSSION...UPDATED 06Z...

QUIET WEATHER WILL PERSIST THROUGH MID AFTERNOON WITH LIGHT/VARIABLE
SOUTH TO SOUTHWEST WINDS BECOMING STEADIER SOUTHWEST LATER THIS
MORNING. VFR WILL CONTINUE BUT CLOUDS WILL THICKEN AND LOWER THIS
AFTERNOON AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM. EXPECT MVFR
TO DEVELOP QUICKLY LATE THIS AFTERNOON.

SNOW WILL SPREAD IN FROM THE SOUTHWEST THIS EVENING..OCCURRING
EARLIEST AT RFD. AREAS SOUTH OF THE TERMINALS MAY SEE PRECIP START
AS A MIX OF RAIN /SLEET/SNOW THEN TRANSITION TO ALL SNOW LATE
EVENING OR OVERNIGHT. HAVE DECENT CONFIDENCE IN TIMING OF THE ONSET
OF SNOW AT THE TERMINALS. LOW LEVEL FLOW WILL BE TURNING
NORTHEASTERLY DURING THE EVENING SO SNOW INTENSITY MAY EASE UP JUST
A BIT AS STEADIER NORTHEAST FLOW DEVELOPS BRINGING IN DRIER AIR. IT
APPEARS THAT SNOW WILL FALL HEAVILY ENOUGH TO BRING IFR VSBY DURING
THE EVENING BUT IT MAY END UP BEING SOMEWHAT
INTERMITTENT...ESPECIALLY FOR A TIME AROUND/AFTER 06Z. SNOW
INTENSITY IS EXPECTED TO INCREASE/PEAK AROUND/AFTER 09Z THEN PERSIST
THROUGH THE REST OF THE MORNING BEFORE WANING AGAIN EARLY SUNDAY
AFTERNOON. SUB 3/4SM OR EVEN 1/2SM VSBY IS MOST LIKELY DURING THIS
TIME. PEAK SNOW ACCUMULATION RATES OF BETWEEN 0.5 AND 0.75 IN/HR ARE
EXPECTED TO BE MOST PREVALENT WITH BRIEF PEAKS NEAR 1.0 IN/HR
POSSIBLE AT TIMES SATURDAY NIGHT AND SUNDAY. SURFACE WINDS WILL TURN
NORTHEASTERLY DURING THE EVENING THEN STEADILY INCREASE IN SPEED
SUNDAY MORNING. GUSTS OF 25-30 KT ARE EXPECTED BY LATE SUNDAY
MORNING WHICH WILL LIKELY RESULT IN BLOWING AND DRIFTING SNOW...AND
GUSTS NEAR 35 KT ARE A POSSIBILITY DURING THE AFTERNOON. WILL ALSO
NEED TO MONITOR LAKE EFFECT SNOW POTENTIAL LATE SUNDAY AFTERNOON
INTO MONDAY MORNING WHICH WOULD LIKELY RESULT IN A RETURN TO IFR
CONDITIONS WITH ADDITIONAL ACCUMULATIONS BUT IT IS NOT CLEAR HOW
LONG THE DURATION MAY BE...ESPECIALLY AT ORD/MDW/DPA.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH MID AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING LATE IN THE AFTERNOON. MEDIUM
  CONFIDENCE IN TIMING OF MVFR ARRIVAL.

* HIGH CONFIDENCE IN SNOW SPREADING IN EARLY/MID EVENING. MEDIUM-
  HIGH CONFIDENCE IN EXACT TIMING. MEDIUM-HIGH CONFIDENCE THAT
  HIGHEST INTENSITY SNOW WILL BEGIN AROUND/AFTER 09Z SUNDAY
  MORNING.

* MEDIUM-HIGH CONFIDENCE IN IFR VSBY OCCURRING DURING THE EVENING AND
  LOW-MEDIUM CONFIDENCE THAT SOME INTERMITTENT IMPROVEMENT WILL
  OCCUR DURING THE EARLY OVERNIGHT. HIGHER CONFIDENCE LOWEST VSBY
  AROUND/AFTER 09Z SUNDAY MORNING.

* HIGH CONFIDENCE IN SOUTHWEST WINDS TURNING NORTHEAST DURING THE
  EVENING. MEDIUM CONFIDENCE IN TIMING. HIGH CONFIDENCE IN SPEEDS
  INCREASING EARLY SUNDAY MORNING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 310543
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1143 PM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 736 PM CST FRI JAN 30 2015

High pressure is dominating the weather across central Illinois
this evening, providing clear skies and calm winds. Radiational
cooling beneath the high has led to a quick temperature drop, with
some locations seeing a 5-6 degree fall between 6pm and 7pm. As
the high shifts eastward later tonight, a light southerly return
flow will develop which will mitigate the rapid cooling. Have adjusted
hourly temps and lowered overnight lows into the teens across the
far north around Lacon. Elsewhere lows will bottom out in the
lower to middle 20s.

&&

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1143 PM CST FRI JAN 30 2015

VFR conditions will prevail through Saturday morning as high
pressure gradually shifts east of the region. Clouds will begin to
thicken/lower by afternoon in advance of an approaching storm
system. All model guidance brings light rain into the area between
19z and 21z, with forecast soundings suggesting ceilings lowering
into the MVFR category at that time. As profiles moisten/cool
further, a rain/snow mix will develop at the terminals prior to
06z.  Have reduced visbys and lowered ceilings to IFR accordingly.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

UPDATE...Barnes
SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Barnes







000
FXUS63 KILX 310543
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1143 PM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 736 PM CST FRI JAN 30 2015

High pressure is dominating the weather across central Illinois
this evening, providing clear skies and calm winds. Radiational
cooling beneath the high has led to a quick temperature drop, with
some locations seeing a 5-6 degree fall between 6pm and 7pm. As
the high shifts eastward later tonight, a light southerly return
flow will develop which will mitigate the rapid cooling. Have adjusted
hourly temps and lowered overnight lows into the teens across the
far north around Lacon. Elsewhere lows will bottom out in the
lower to middle 20s.

&&

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1143 PM CST FRI JAN 30 2015

VFR conditions will prevail through Saturday morning as high
pressure gradually shifts east of the region. Clouds will begin to
thicken/lower by afternoon in advance of an approaching storm
system. All model guidance brings light rain into the area between
19z and 21z, with forecast soundings suggesting ceilings lowering
into the MVFR category at that time. As profiles moisten/cool
further, a rain/snow mix will develop at the terminals prior to
06z.  Have reduced visbys and lowered ceilings to IFR accordingly.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

UPDATE...Barnes
SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Barnes






000
FXUS63 KLOT 310306
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
906 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310306
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
906 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310306
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
906 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310306
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
906 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310247
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
847 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 310247
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
847 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 310247
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
847 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 310247
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
847 PM CST FRI JAN 30 2015

.UPDATE...

847 PM...EVENING UPDATE...NO CHANGES PLANNED TO CURRENT WINTER
STORM WATCH. WHILE THE 00Z NAM IS ROLLING IN WITH NO SIGNIFICANT
CHANGES FROM 12Z/18Z NAM RUNS...WILL ALLOW MIDNIGHT SHIFT TO
EVALUATE THE FULL SUITE OF 00Z GUIDANCE BEFORE MAKING ANY UPGRADE
DECISIONS AS WELL AS AMOUNTS.

IN THE SHORT TERM...MAINLY CLEAR SKIES AND LIGHT WINDS HAVE
ALLOWED TEMPS TO DIP INTO THE TEENS IN SOME LOCATIONS...BUT AS THE
GRADIENT SLOWLY TIGHTENS FROM WEST TO EAST...ALONG WITH SOME MID/
HIGH LEVEL CLOUD COVER...TEMPS WILL LIKELY LEVEL OFF AND POSSIBLY
BECOME STEADY OVERNIGHT. CMS

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 310136
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
736 PM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 736 PM CST FRI JAN 30 2015

High pressure is dominating the weather across central Illinois
this evening, providing clear skies and calm winds. Radiational
cooling beneath the high has led to a quick temperature drop, with
some locations seeing a 5-6 degree fall between 6pm and 7pm. As
the high shifts eastward later tonight, a light southerly return
flow will develop which will mitigate the rapid cooling. Have adjusted
hourly temps and lowered overnight lows into the teens across the
far north around Lacon. Elsewhere lows will bottom out in the
lower to middle 20s.

&&

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 539 PM CST FRI JAN 30 2015

Clear skies/light winds will prevail across central Illinois this
evening before high/thin cloudiness begins to increase from the
west overnight. Latest model runs bring precip into the area
slightly faster than previously expected, with consensus showing
light rain developing between 19z and 21z Sat. Winds will
gradually veer to the southwest and increase to around 10kt by
midday Sat.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

UPDATE...Barnes
SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Barnes







000
FXUS63 KLOT 310015
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
615 PM CST FRI JAN 30 2015

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

...WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

.LONG TERM...MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 310015
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
615 PM CST FRI JAN 30 2015

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

...WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

.LONG TERM...MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* NONE THROUGH MID SATURDAY AFTERNOON.

* CIGS LOWER TO MVFR LATE SATURDAY AFTERNOON.

* SNOW ARRIVES EARLY SATURDAY EVENING BRINGING LOWERING CIGS AND
  IFR VSBY.

* SOUTHWEST WINDS TURN NORTHEAST SATURDAY EVENING.

MDB

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE IS MOVING EAST ACROSS THE AREA THIS EVENING WITH
WINDS BECOMING STEADIER FROM THE SOUTHWEST. A LAKE INFLUENCE HAS
TURNED WINDS OFF THE LAKE BETWEEN NORTHEAST AND SOUTHEAST NEAR THE
LAKE BUT THIS WILL BE FADING IN FAVOR OF SOUTHWESTERLY WINDS.
SOUTHWEST WINDS WILL COME UP TOWARDS 10 KT SATURDAY MORNING THEN
EASE UP LATE IN THE DAY AS THE PRESSURE GRADIENT SLACKENS.

CONDITIONS WILL DETERIORATE SATURDAY EVENING AS LOW PRESSURE
MOVES ACROSS THE CENTRAL PLAINS. CIGS WILL STEADILY LOWER LATE IN THE
DAY AND LIKELY BE MVFR BY LATE AFTERNOON. SNOW WILL SPREAD IN FROM
THE SOUTHWEST DURING THE EARLY TO MID EVENING AND CONTINUE THROUGH
SUNDAY. PEAK SNOW INTENSITY LOOKS TO BE SATURDAY NIGHT THROUGH
MIDDAY SUNDAY BEFORE EASING UP SUNDAY AFTERNOON...WITH 0.5 TO 1
INCH PER HOUR ACCUMULATION RATES EXPECTED. VSBY WILL LIKELY FALL
TO LESS THAN 1/2SM AT TIMES AS WELL. WINDS WILL TURN NORTHEASTERLY
SATURDAY EVENING AND INCREASE IN SPEED SUNDAY MORNING WITH GUSTS
NEAR 30 KT POSSIBLE. LAKE EFFECT/ENHANCEMENT BECOMES A CONCERN FOR
ORD/MDW/DPA/GYY LATE SUNDAY AFTERNOON INTO SUNDAY EVENING AS WINDS
TURN NORTHERLY. IF THIS MATERIALIZES SNOWFALL RATES WOULD INCREASE
AGAIN FOR A TIME WITH THE FOCUS TRANSITIONING FROM NE ILLINOIS TOWARD
NW INDIANA SUNDAY NIGHT INTO MONDAY MORNING.

MDB


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE IN THE FORECAST THROUGH SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN CIGS LOWERING TO MVFR LATER SATURDAY AFTERNOON.

* HIGH CONFIDENCE IN SNOW ARRIVING BY MID SATURDAY EVENING. MEDIUM
  CONFIDENCE IN SPECIFIC TIMING. MEDIUM-HIGH CONFIDENCE IN QUICK
  REDUCTION TO IFR VSBY IN SNOW.

* MEDIUM-HIGH CONFIDENCE IN TIMING OF WINDS SHIFTING FROM
  SOUTHWEST TO NORTHEAST SATURDAY EVENING.

MDB

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS WITH PERIODS OF IFR CONDITIONS EXPECTED...ESPECIALLY
DURING THE MORNING.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

MDB

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KILX 302339
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
539 PM CST Fri Jan 30 2015

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 539 PM CST FRI JAN 30 2015

Clear skies/light winds will prevail across central Illinois this
evening before high/thin cloudiness begins to increase from the
west overnight. Latest model runs bring precip into the area
slightly faster than previously expected, with consensus showing
light rain developing between 19z and 21z Sat. Winds will
gradually veer to the southwest and increase to around 10kt by
midday Sat.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Barnes







000
FXUS63 KLOT 302209
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
409 PM CST FRI JAN 30 2015

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

...WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

.LONG TERM...MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS TURN SOUTHWEST TO SOUTH INTO SATURDAY MORNING. WITH SPEEDS
  AROUND 5-7KT.

MDB

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 302209
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
409 PM CST FRI JAN 30 2015

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

...WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

.LONG TERM...MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS TURN SOUTHWEST TO SOUTH INTO SATURDAY MORNING. WITH SPEEDS
  AROUND 5-7KT.

MDB

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

MDB

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATCHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS
EAST MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND
TUESDAY NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND
WILL SEND ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 302128
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
328 PM CST Fri Jan 30 2015

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Geelhart






000
FXUS63 KILX 302128
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
328 PM CST Fri Jan 30 2015

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Geelhart






000
FXUS63 KILX 302128
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
328 PM CST Fri Jan 30 2015

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Geelhart






000
FXUS63 KILX 302128
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
328 PM CST Fri Jan 30 2015

.SHORT TERM...(Tonight)
ISSUED AT 327 PM CST FRI JAN 30 2015

Little happening in the short term, as axis of high pressure extends
northeast-southwest across the forecast area this afternoon. Cirrus
clouds beginning to spread eastward across the Missouri/Illinois
border ahead of the organizing storm system to our southwest, and
skies will become partly cloudy overnight. Coolest conditions
expected over the northeast CWA where less cloud cover is
anticipated, with lows near 20. Temperatures not expected to move
much after midnight as southerly winds start to increase.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 327 PM CST FRI JAN 30 2015

Models have shifted a tad north again with the track/location of the
heaviest snowfall with the approaching weekend system. As with
previous systems that have moved across the area the past couple of
months, our CWA will be right in the middle of where two mid level
troughs will be phasing together. On the surface, the low pressure
area is still developing in the southwestern US and will not move
out into the southern plains until Saturday evening. However, a cold
front will be dropping down into Illinois at the same time, and how
far this gets into central Illinois will determine where the cutoff
of the warm air and cold air is, which will also determine where the
heavy snowfall will occur. Models are in fairly good agreement, but
have trended north, so there remains some uncertainty as to amounts
and locations of the heaviest snowfall this weekend. What is known,
is that precip will begin Sat afternoon in the west and then
progress eastward through the night and continue through Sunday,
then taper off and end Sun night. The question still remains pcpn
type. Based on current forecast guidance, the precip should be
either rain or snow, or a mix. Conditions do not look favorable for
the other types of winter weather at this time; i.e. freezing rain
and sleet.

So after considerable analysis and discussions with surrounding
offices, we have come to a consensus with the forecast for this
weekend. With the resulting low pressure area tracking eastward
across southern Illinois, it looks like the heaviest snowfall will
be along and north of a Rushville to Danville line Saturday night
through Sunday. With decent isentropic lift and sufficient moisture
to work with, believe highest amounts will be in the 7 to 9 inch
range. Just south of that line, snowfall amounts look to be in the 5
to 7 inch range. Lesser amounts will be likely south of this area,
in southeast Illinois, due to the warmer temps hanging around Sat
night into Sunday morning...and the possibility of the precip being
a mix of rain and snow. This area, the amounts should be roughly in
the 3 to 5 inch range, and will include the I-70 area.

So based on this, we have already issued a Winter Storm Watch for
most of central and eastern Illinois, beginning tomorrow at 6 pm and
continuing through midnight Sunday night. The bulk of the snow,
especially in the north, should fall between 6 pm Sat through 6 pm
Sun. If the warm air get further north and/or hangs around longer,
or the low tracks a little further north then snowfall totals will
be much less across the whole area. Due to these continued
uncertainties and possible changes, it was decided not to go with a
warning and just keep the watch going at this time.

Beyond the weekend system, conditions will be relatively dry. After
a cold day on Mon, temps will rise to around freezing for Tue. Then
temps will fall again to below freezing for the rest of the week.
There is a couple of weak waves coming through but moisture appears
limited, so there will not be any mentionable pcpn in the forecast at
this time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday evening
FOR ILZ027>031-036>038-040>057.

&&

$$

SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Geelhart






000
FXUS63 KLOT 302117
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 PM CST FRI JAN 30 2015

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

...WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

.LONG TERM...MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT FROM THE NORTHWEST...SLOWLY TURNING WEST/SOUTHWEST
  WITH SPEEDS AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 302117
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 PM CST FRI JAN 30 2015

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY MORNING...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

317 PM CST...

...WINTER STORM...SATURDAY AFTERNOON THROUGH EARLY MONDAY...

HEADLINES: HAVE CONTINUED WITH WINTER STORM WATCH FOR ENTIRE CWA
SATURDAY EVENING THROUGH LATE SUNDAY NIGHT/EARLY MONDAY. PART OF
THE EVOLUTION OF THE STORM IS TIED TO THE TRACK AND STRENGTH OF
NORTHERN STREAM ENERGY MOVING ONTO THE BRITISH COLUMBIA COAST THIS
MORNING THAT WAS ONLY PARTIALLY SAMPLED BY THE UPPER AIR NETWORK.
THUS WHILE CONFIDENCE IS INCREASING ON A VERY SIGNIFICANT WINTER
STORM...CONFIDENCE IS NOT HIGH ENOUGH YET (80%+) IN TOTAL AMOUNTS
TO ISSUE A WARNING.

WE ARE STILL LOOKING AT A LONG DURATION PRIMARILY MODERATE SNOW
EVENT. HOWEVER...IT MUST BE NOTED THAT THE MUCH OF THE GUIDANCE
HAS TRENDED STRONGER AND FARTHER NORTH WITH THE SURFACE AND
MIDLEVEL LOWS THAT WILL IMPACT THE AREA. ENERGY FROM SOUTHWEST
CLOSED LOW WILL EJECT AND INTERACT WITH A STRONG NORTHERN WAVE
DIVING SOUTHEAST TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS
WILL RESULT IN INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN
ADVANCE OF AN INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS
SATURDAY EVENING AND NIGHT. AT THE SAME TIME...COLDER AIR WILL
OOZE SOUTHWARD BEHIND COLD FRONT EMANATING FROM STRONG ARCTIC
HIGH PRESSURE SPREADING SOUTHEAST FROM THE CANADIAN PRAIRIES.

LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING MAINLY SATURDAY
EVENING...BUT POSSIBLY AS EARLY AS THE LATE AFTERNOON IN THE FAR
SOUTHWEST CWA AS TOP DOWN SATURATION OCCURS. BOUNDARY LAYER
CONDITIONS WILL BE A BIT MARGINAL IN THESE AREAS...BUT MAX WET BULB
TEMPS ARE JUST SLIGHTLY ABOVE FREEZING...SO ANY RA/SN MIX THAT
OCCURS SHOULD QUICKLY TRANSITION TO SNOW...BUT WITH LOWER RATIOS
CLOSER TO 10:1. CAVEAT TO THIS WILL BE IF SYSTEM AND 850 MB LOW
TRACK CONTINUES NORTHWARD SHIFT ON GUIDANCE...PARTS OF SOUTHERN
CWA MAY FLIRT WITH MARGINAL THERMAL PROFILES LATER INTO SATURDAY
EVENING.

SNOW WILL OVERSPREAD THE AREA FROM WEST-SOUTHWEST TO EAST
NORTHEAST DURING SATURDAY EVENING...WITH CONDITIONS DETERIORATING
OVERNIGHT. WHILE SNOWFALL RATES WILL GENERALLY BE MODERATE (1/2"
TO 1"/HR)...STRENGTHENING 700 MB FGEN LAYING OUT ROUGHLY ALONG
I-80 BY LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING COULD RESULT
IN OCCASIONAL HEAVY RATES (1-2"/HR). AS SURFACE LOW TRACKS FROM
NORTHERN/CENTRAL MO TO CENTRAL IL DURING THE DAY ON SUNDAY...THE
DEFORMATION AXIS OF THE STRENGTHENING SURFACE AND MID LEVEL LOWS
WILL LINGER INTO LATE SUNDAY...KEEPING LIGHT TO MODERATE SNOW
GOING. IN ADDITION...850 MB LOW TRACK IS PROGGED TO TAKE NEARLY
IDEAL TRACK FOR SIGNIFICANT SNOW IN THE CWA FROM CENTRAL IL INTO
CENTRAL INDIANA. FINALLY...ON SUNDAY NIGHT...WHILE SNOW WILL TAPER
OFF FOR MUCH OF NORTH CENTRAL IL...IMPROVING THERMODYNAMICS AND
NORTH-NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN IS EXPECTED
TO RESULT IN LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT
SNOW. BUFKIT SOUNDINGS ARE INDICATING IN EXCESS OF 200 J/KG OF
LAKE INDUCED CAPE. WHILE INVERSION HEIGHTS WILL BE SOMEWHAT
MARGINAL...LIFT WILL BE THROUGH DGZ AND ALSO HIGHER-RES GUIDANCE
IS INDICATING VERY STRONG CONVERGENCE DEVELOPING. HAVE BUMPED UP
POPS TO LIKELY INTO NE IL AND EXTREME NW INDIANA...BUT CONFIDENCE
IS LOW ON EXACTLY HOW MUCH SNOW WILL BE ADDED BY LAKE EFFECT INTO
EARLY MONDAY.

DESPITE LONG DURATION PRIMARILY MODERATE SNOW...HAZARD POSED BY
THIS STORM IS LIKELY TO BE MAGNIFIED BY STRENGTHENING PRESSURE
GRADIENT SUNDAY MORNING INTO SUNDAY NIGHT. TRACK OF LOW FOLLOWED
BY ARCTIC HIGH SPREADING SOUTHEAST IN ITS WAKE WILL RESULT IN
STRONG ISALLOBARIC PRESSURE FALLS FOLLOWED BY PRESSURE RISES. IF
SOME OF THE STRONGER SURFACE LOW SOLUTIONS ON GUIDANCE COME TO
FRUITION...THIS WILL BE EVEN MORESO THE CASE. DURING THIS
TIMEFRAME...SNOW WILL BE INCREASINGLY FLUFFY...SO BLOWING SNOW DUE
TO NORTHEAST WIND GUSTS OF 30-35 MPH COULD COMBINE WITH FALLING
SNOW TO RESULT IN NEAR BLIZZARD CONDITIONS IN OPEN AREAS. ON THE
IMMEDIATE LAKEFRONT...WIND GUSTS FROM THE FRICTIONLESS LAKE COULD
EVEN TOUCH 40 MPH...POTENTIALLY RESULTING IN NEAR BLIZZARD
CONDITIONS THERE. CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN
SLIGHTLY STRONGER WINDS ON THE LAKEFRONT SUNDAY NIGHT INTO EARLY
MONDAY MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED
VISIBILITY GOING WHILE WINDS DIMINISH FOR THE REST OF THE AREA. AS
A FINAL ADDITIONAL NOTE ON THE LAKEFRONT...INCREASING CONCERN FOR
AT LEAST MINOR LAKESHORE FLOODING IN NE IL BY SUNDAY EVENING DUE
TO WAVES BUILDING TO 10 TO 14 FT. HAVE NOT ISSUED A LAKESHORE
FLOOD WATCH...BUT MAY NEED TO CONSIDER A LAKESHORE FLOOD ADVISORY.

OVERALL...CONTINUE TO HAVE HIGHEST CONFIDENCE IN GREATER THAN 8
INCH SNOW AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE
FROM WINTHROP HARBOR TO FORRESTON IL. LOCALLY HIGHER AMOUNTS IN
EXCESS OF A FOOT ARE POSSIBLE NEAR LAKE MICHIGAN AND ALONG/SOUTH
OF INTERSTATE 88. NORTHWEST OF THAT LINE...INCLUDING THE ROCKFORD
METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS EVEN IF STRICT WARNING CRITERIA OF 8 INCHES IN 24 HOURS IS
NOT MET.

RC

&&

.LONG TERM...
317 PM CST

.LONG TERM...MONDAY MORNING THROUGH THURSDAY...

TRANSITORY AND WEAKENING SURFACE HIGH PRESSURE MOVES THROUGH THE
AREA ON MONDAY. AS THIS OCCURS LOW LEVEL FLOW WHICH INITIALLY STILL
BE SLIGHTLY EAST OF NORTH WILL TURN NORTHWESTERLY THROUGH THE DAY.
LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN DURING THE MORNING
PERIOD AS SIGNIFICANT DRYING IN THE 850-700 LAYER OCCURS AND WINDS
BACK TO NORTHWESTERLY...WITH ANY ACTIVITY EAST OF THE AREA BY MID
AFTERNOON. DESPITE SUNNY SKIES...COLD NORTH WINDS AND A FRESH
SNOWPACK WILL MEAN HIGHS IN THE TEENS.

NO REST FOR THE WEARY...AS THE FLOW REMAINS ACTIVE IN FOR MID WEEK.
FORTUNATELY THE INITIAL COLD ON MONDAY WILL BE SHORT LIVED AS THE
STRONG ARCTIC HIGH WEAKENS AND SHIFTS EAST MONDAY NIGHT. WNW FLOW
ALOFT WILL PERSIST OVER THE AREA WITH FAST MOVING PACIFIC SYSTEM
PASSING THROUGH THE REGION...AND A BAROCLINIC ZONE DRAPED SOMEWHERE
OVER THE REGION AS WELL. THIS SETS THE STAGE FOR QUICK
MOVING...BUT GENERALLLY WEAKER SYSTEMS...BUT LOOKS LIKE THE
POTENTIAL FOR PERIODS OF MOSTLY LIGHT SNOW. THE FIRST MOVES THROUGH
MONDAY NIGHT WITH SOME VERY LIGHT SNOW POSSIBLE. A SECOND SYSTEM IS
ON ITS HEELS FOR TUESDAY EVENING WHICH PRESENTS MORE OF A SMALL
P-TYPE CONCERN. AFTERWARDS...A STRENGTHENING ARCTIC HIGH WILL MOVE
INTO THE NORTHERN PLAINS ON WEDNESDAY. AHEAD OF THE HIGH A COLD
FRONT MAY PROVIDE THE FOCUS FOR ADDITIONAL SNOW...FOLLOWED BY
ANOTHER GLANCING BLOW OF ARCTIC AIR THURSDAY INTO FRIDAY WITH HIGHS
IN THE TEENS AND LOWS SURROUNDING BOTH SIDES OF THE ZERO DEGREE
MARK...WIND CHILLS POSSIBLY GETTING NEARING -10 OR SO THURSDAY
NIGHT.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT FROM THE NORTHWEST...SLOWLY TURNING WEST/SOUTHWEST
  WITH SPEEDS AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 301945
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
145 PM CST FRI JAN 30 2015

.UPDATE...

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT FROM THE NORTHWEST...SLOWLY TURNING WEST/SOUTHWEST
  WITH SPEEDS AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 301945
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
145 PM CST FRI JAN 30 2015

.UPDATE...

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT FROM THE NORTHWEST...SLOWLY TURNING WEST/SOUTHWEST
  WITH SPEEDS AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 301945
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
145 PM CST FRI JAN 30 2015

.UPDATE...

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT FROM THE NORTHWEST...SLOWLY TURNING WEST/SOUTHWEST
  WITH SPEEDS AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 301945
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
145 PM CST FRI JAN 30 2015

.UPDATE...

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT FROM THE NORTHWEST...SLOWLY TURNING WEST/SOUTHWEST
  WITH SPEEDS AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 301940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
140 PM CST FRI JAN 30 2015

.UPDATE...1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT...SLOWLY TURNING WEST/SOUTHWEST WITH SPEEDS
  AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 301940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
140 PM CST FRI JAN 30 2015

.UPDATE...1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT...SLOWLY TURNING WEST/SOUTHWEST WITH SPEEDS
  AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
139 PM CST

A BRIEF REPRIEVE FOR THE LAKE WILL BE SHORT LIVED AS MODERATELY STRONG
HIGH PRESSURE OVERHEAD SHIFTS EASTWARD TONIGHT. WEAK LOW PRESSURE IN
THE CANADIAN PRAIRIES WILL PUSH EAST TO LAKE SUPERIOR TONIGHT
SHIFTING WINDS TO SOUTHWESTERLY. STRONG ARCTIC HIGH PRESSURE IN
SASKATECHEWAN WILL PUSH INTO INTO THE NORTHERN PLAINS BY SUNDAY
AFTERNOON. MEANWHILE...LOW PRESSURE WILL EJECT FROM THE ROCKIES
SATURDAY NIGHT AND MOVE NORTHEAST THROUGH THE OHIO VALLEY SUNDAY
AFTERNOON AND EVENING...WHICH WILL ALLOW A COLD FRONT TO MOVE DOWN
THE LAKE. THIS TRACK COULD CREATE NORTHEASTERLY GALE CONDITIONS ON
THE LAKE SUNDAY AFTERNOON AND EVENING...ESPECIALLY ON THE SOUTH
HALF. THE WEAKENING HIGH MOVES OVER THE LAKE MONDAY THEN SHIFTS EAST
MONDAY NIGHT. ANOTHER WEAK LOW PASSES OVER MID LAKE AROUND TUESDAY
NIGHT...THEN HIGH PRESSURE REBUILDS INTO THE PLAINS AND WILL SEND
ANOTHER COLD FRONT OVER THE LAKE INTO THURSDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WATCH...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO MIDNIGHT MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KLOT 301757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1157 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT...SLOWLY TURNING WEST/SOUTHWEST WITH SPEEDS
  AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1157 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT...SLOWLY TURNING WEST/SOUTHWEST WITH SPEEDS
  AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1157 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT...SLOWLY TURNING WEST/SOUTHWEST WITH SPEEDS
  AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1157 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT...SLOWLY TURNING WEST/SOUTHWEST WITH SPEEDS
  AROUND 5-7KT.

BEACHLER

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 301736
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1136 AM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 1135 AM CST FRI JAN 30 2015

After coordination with WPC and surrounding offices, a winter
storm watch is being issued for a large part of our forecast area,
except along and south of I-70. Forecast soundings from the
southeast CWA indicate a fair amount of mixed precip or even rain
on Sunday, lowering the threat of significant snowfall in that
area. Further north, heavier amounts of 6-8 inches are indicated
north of a Havana to Paris line, with the heaviest snow axis
expected to set up a little further north in east central
Illinois. Updated products will be out shortly.


UPDATE ISSUED AT 945 AM CST FRI JAN 30 2015

Little change needed to the morning forecast, but did update high
temperatures a degree or two in some areas. Band of altocumulus
in the upper Mississippi Valley is tracking southeast, but the
trajectory would favor the thicker clouds staying just to our
northeast. Some increase in cirrus expected from the west as well,
but skies generally to remain mostly sunny as ridge axis moves on
top of us.

Early look at the 12Z NAM for this weekend continues to favor the
northern half of the forecast area for the heavier snow amounts,
with the GFS just starting to arrive. Will be coordinating with
WPC and neighboring offices on any headlines, which may be issued
before the regular afternoon forecast package.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 MB high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the SW states to deepen surface low
pressure NE into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
SW counties Sat evening. Models have trended heavier with QPF close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from NW
to SE and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy SSW winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front SE
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday
afternoon FOR ILZ027>031-036>038-040>057.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...07
AVIATION...Geelhart






000
FXUS63 KILX 301736
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1136 AM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 1135 AM CST FRI JAN 30 2015

After coordination with WPC and surrounding offices, a winter
storm watch is being issued for a large part of our forecast area,
except along and south of I-70. Forecast soundings from the
southeast CWA indicate a fair amount of mixed precip or even rain
on Sunday, lowering the threat of significant snowfall in that
area. Further north, heavier amounts of 6-8 inches are indicated
north of a Havana to Paris line, with the heaviest snow axis
expected to set up a little further north in east central
Illinois. Updated products will be out shortly.


UPDATE ISSUED AT 945 AM CST FRI JAN 30 2015

Little change needed to the morning forecast, but did update high
temperatures a degree or two in some areas. Band of altocumulus
in the upper Mississippi Valley is tracking southeast, but the
trajectory would favor the thicker clouds staying just to our
northeast. Some increase in cirrus expected from the west as well,
but skies generally to remain mostly sunny as ridge axis moves on
top of us.

Early look at the 12Z NAM for this weekend continues to favor the
northern half of the forecast area for the heavier snow amounts,
with the GFS just starting to arrive. Will be coordinating with
WPC and neighboring offices on any headlines, which may be issued
before the regular afternoon forecast package.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 MB high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the SW states to deepen surface low
pressure NE into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
SW counties Sat evening. Models have trended heavier with QPF close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from NW
to SE and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy SSW winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front SE
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday
afternoon FOR ILZ027>031-036>038-040>057.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...07
AVIATION...Geelhart






000
FXUS63 KILX 301736
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1136 AM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 1135 AM CST FRI JAN 30 2015

After coordination with WPC and surrounding offices, a winter
storm watch is being issued for a large part of our forecast area,
except along and south of I-70. Forecast soundings from the
southeast CWA indicate a fair amount of mixed precip or even rain
on Sunday, lowering the threat of significant snowfall in that
area. Further north, heavier amounts of 6-8 inches are indicated
north of a Havana to Paris line, with the heaviest snow axis
expected to set up a little further north in east central
Illinois. Updated products will be out shortly.


UPDATE ISSUED AT 945 AM CST FRI JAN 30 2015

Little change needed to the morning forecast, but did update high
temperatures a degree or two in some areas. Band of altocumulus
in the upper Mississippi Valley is tracking southeast, but the
trajectory would favor the thicker clouds staying just to our
northeast. Some increase in cirrus expected from the west as well,
but skies generally to remain mostly sunny as ridge axis moves on
top of us.

Early look at the 12Z NAM for this weekend continues to favor the
northern half of the forecast area for the heavier snow amounts,
with the GFS just starting to arrive. Will be coordinating with
WPC and neighboring offices on any headlines, which may be issued
before the regular afternoon forecast package.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 MB high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the SW states to deepen surface low
pressure NE into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
SW counties Sat evening. Models have trended heavier with QPF close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from NW
to SE and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy SSW winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front SE
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday
afternoon FOR ILZ027>031-036>038-040>057.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...07
AVIATION...Geelhart






000
FXUS63 KILX 301736
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1136 AM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 1135 AM CST FRI JAN 30 2015

After coordination with WPC and surrounding offices, a winter
storm watch is being issued for a large part of our forecast area,
except along and south of I-70. Forecast soundings from the
southeast CWA indicate a fair amount of mixed precip or even rain
on Sunday, lowering the threat of significant snowfall in that
area. Further north, heavier amounts of 6-8 inches are indicated
north of a Havana to Paris line, with the heaviest snow axis
expected to set up a little further north in east central
Illinois. Updated products will be out shortly.


UPDATE ISSUED AT 945 AM CST FRI JAN 30 2015

Little change needed to the morning forecast, but did update high
temperatures a degree or two in some areas. Band of altocumulus
in the upper Mississippi Valley is tracking southeast, but the
trajectory would favor the thicker clouds staying just to our
northeast. Some increase in cirrus expected from the west as well,
but skies generally to remain mostly sunny as ridge axis moves on
top of us.

Early look at the 12Z NAM for this weekend continues to favor the
northern half of the forecast area for the heavier snow amounts,
with the GFS just starting to arrive. Will be coordinating with
WPC and neighboring offices on any headlines, which may be issued
before the regular afternoon forecast package.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 MB high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the SW states to deepen surface low
pressure NE into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
SW counties Sat evening. Models have trended heavier with QPF close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from NW
to SE and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy SSW winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front SE
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1135 AM CST FRI JAN 30 2015

VFR conditions to remain on tap through the forecast period. We
are seeing some stratocumulus developing over the eastern half of
Illinois around 2000 feet, but this should remain scattered for
the most part. General trend will be for high clouds to spread in
from the west later tonight and especially on Saturday. Northeast
winds have started to become light and variable as an axis of high
pressure moves overhead, but will trend more south/southwest this
evening as the axis moves to the east.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH from Saturday evening through Sunday
afternoon FOR ILZ027>031-036>038-040>057.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...07
AVIATION...Geelhart






000
FXUS63 KLOT 301729
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1129 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301712
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1112 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO








000
FXUS63 KLOT 301712
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1112 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO







000
FXUS63 KILX 301547
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
947 AM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 945 AM CST FRI JAN 30 2015

Little change needed to the morning forecast, but did update high
temperatures a degree or two in some areas. Band of altocumulus
in the upper Mississippi Valley is tracking southeast, but the
trajectory would favor the thicker clouds staying just to our
northeast. Some increase in cirrus expected from the west as well,
but skies generally to remain mostly sunny as ridge axis moves on
top of us.

Early look at the 12Z NAM for this weekend continues to favor the
northern half of the forecast area for the heavier snow amounts,
with the GFS just starting to arrive. Will be coordinating with
WPC and neighboring offices on any headlines, which may be issued
before the regular afternoon forecast package.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 MB high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the SW states to deepen surface low
pressure NE into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
SW counties Sat evening. Models have trended heavier with QPF close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from NW
to SE and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy SSW winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front SE
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 542 AM CST FRI JAN 30 2015

Mainly quiet/VFR aviation weather conditions expected across the
central Illinois terminals through the 12Z TAF valid time. Skies
have become mostly clear across much of the area in the past few
hours, and cloud cover through the remainder of the period is
expected to remain minimal. However, will have to monitor some of
the MVFR cigs that still exist upstream across the upper Midwest
and see if any of them can hold together as they stream this way.
Northwest winds will diminish early this morning, becoming
light/variable as high pressure builds into the area. Winds are
then expected to trend southerly tonight as the high pressure
ridge pushes east of the area.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...07
AVIATION...Bak






000
FXUS63 KILX 301547
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
947 AM CST Fri Jan 30 2015

.UPDATE...
ISSUED AT 945 AM CST FRI JAN 30 2015

Little change needed to the morning forecast, but did update high
temperatures a degree or two in some areas. Band of altocumulus
in the upper Mississippi Valley is tracking southeast, but the
trajectory would favor the thicker clouds staying just to our
northeast. Some increase in cirrus expected from the west as well,
but skies generally to remain mostly sunny as ridge axis moves on
top of us.

Early look at the 12Z NAM for this weekend continues to favor the
northern half of the forecast area for the heavier snow amounts,
with the GFS just starting to arrive. Will be coordinating with
WPC and neighboring offices on any headlines, which may be issued
before the regular afternoon forecast package.

&&

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 MB high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the SW states to deepen surface low
pressure NE into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
SW counties Sat evening. Models have trended heavier with QPF close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from NW
to SE and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy SSW winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front SE
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 542 AM CST FRI JAN 30 2015

Mainly quiet/VFR aviation weather conditions expected across the
central Illinois terminals through the 12Z TAF valid time. Skies
have become mostly clear across much of the area in the past few
hours, and cloud cover through the remainder of the period is
expected to remain minimal. However, will have to monitor some of
the MVFR cigs that still exist upstream across the upper Midwest
and see if any of them can hold together as they stream this way.
Northwest winds will diminish early this morning, becoming
light/variable as high pressure builds into the area. Winds are
then expected to trend southerly tonight as the high pressure
ridge pushes east of the area.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...07
AVIATION...Bak







000
FXUS63 KLOT 301420
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
820 AM CST FRI JAN 30 2015

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO






000
FXUS63 KLOT 301420
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
820 AM CST FRI JAN 30 2015

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN/BEACHLER

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN/BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
549 AM CST FRI JAN 30 2015

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
549 AM CST FRI JAN 30 2015

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
549 AM CST FRI JAN 30 2015

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 301149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
549 AM CST FRI JAN 30 2015

.SHORT TERM...
313 AM CST

THROUGH TONIGHT...

WEATHER NIL IN THE SHORT TERM TIME FRAME AS HIGH PRESSURE MOVES
ACROSS THE REGION THROUGH TONIGHT WITH SOUTHERLY WINDS AND WARM AIR
ADVECTION KICKING IN LATE TONIGHT AS THE HIGH MOVES EAST OF THE
REGION.

IZZI

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NNWLY WINDS BACKING TO SWLY THIS AFTERNOON. SPEED LESS THAN 10KT
  THROUGH THE DAY.

KREIN

//DISCUSSION...UPDATED 12Z...

HIGH PRESSURE SLIDING ACROSS THE REGION TODAY WILL KEEP SKIES
MOSTLY CLEAR. WINDS WILL ALSO DIMINISH A BIT FROM THE INITIAL
8-9KT THIS MORNING AND BACK TO SWLY THIS AFTERNOON AS THE CENTER
OF THE HIGH MOVES ACROSS NRN IL AND INTO CNTRL INDIANA. WINDS WILL
THEN BE LIGHT AND SWLY THROUGH THE REMAINDER OF THE FORECAST
PERIOD AS THE HIGH SETTLES INTO THE OHIO VALLEY.

KREIN


//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KILX 301142
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
542 AM CST Fri Jan 30 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 mb high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the sw states to deepen surface low
pressure ne into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
sw counties Sat evening. Models have trended heavier with qpf close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from nw
to se and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy ssw winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front se
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 542 AM CST FRI JAN 30 2015

Mainly quiet/VFR aviation weather conditions expected across the
central Illinois terminals through the 12Z TAF valid time. Skies
have become mostly clear across much of the area in the past few
hours, and cloud cover through the remainder of the period is
expected to remain minimal. However, will have to monitor some of
the MVFR cigs that still exist upstream across the upper Midwest
and see if any of them can hold together as they stream this way.
Northwest winds will diminish early this morning, becoming
light/variable as high pressure builds into the area. Winds are
then expected to trend southerly tonight as the high pressure
ridge pushes east of the area.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Bak
LONG TERM...07
AVIATION...Bak







000
FXUS63 KILX 301142
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
542 AM CST Fri Jan 30 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 mb high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the sw states to deepen surface low
pressure ne into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
sw counties Sat evening. Models have trended heavier with qpf close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from nw
to se and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy ssw winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front se
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 542 AM CST FRI JAN 30 2015

Mainly quiet/VFR aviation weather conditions expected across the
central Illinois terminals through the 12Z TAF valid time. Skies
have become mostly clear across much of the area in the past few
hours, and cloud cover through the remainder of the period is
expected to remain minimal. However, will have to monitor some of
the MVFR cigs that still exist upstream across the upper Midwest
and see if any of them can hold together as they stream this way.
Northwest winds will diminish early this morning, becoming
light/variable as high pressure builds into the area. Winds are
then expected to trend southerly tonight as the high pressure
ridge pushes east of the area.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Bak
LONG TERM...07
AVIATION...Bak







000
FXUS63 KILX 301142
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
542 AM CST Fri Jan 30 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 mb high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the sw states to deepen surface low
pressure ne into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
sw counties Sat evening. Models have trended heavier with qpf close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from nw
to se and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy ssw winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front se
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 542 AM CST FRI JAN 30 2015

Mainly quiet/VFR aviation weather conditions expected across the
central Illinois terminals through the 12Z TAF valid time. Skies
have become mostly clear across much of the area in the past few
hours, and cloud cover through the remainder of the period is
expected to remain minimal. However, will have to monitor some of
the MVFR cigs that still exist upstream across the upper Midwest
and see if any of them can hold together as they stream this way.
Northwest winds will diminish early this morning, becoming
light/variable as high pressure builds into the area. Winds are
then expected to trend southerly tonight as the high pressure
ridge pushes east of the area.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Bak
LONG TERM...07
AVIATION...Bak







000
FXUS63 KILX 301142
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
542 AM CST Fri Jan 30 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Consensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL where mix precipitation to occur Sat
afternoon/evening before changing to all snow by overnight Sat night
into Sunday. Will issue another SPS to address the potential of several
inches of snow accumulations Saturday night and Sunday especially
from I-72 north. A winter storm watch may eventually be needed
Saturday night and Sunday especially over northern counties.

1037 mb high pressure over MN into the central plains will drift
east into the Ohio river valley by midnight tonight and into the mid
Atlantic States Sat morning and continue dry weather over central
and eastern IL. Lows tonight mostly in the lower 20s with a few
upper teens from Champaign and Paris northeast.

Low pressure organizing in the sw states to deepen surface low
pressure ne into the central Ohio river valley by sunset Sunday.
This to spread mixed precipitation into central IL during Sat
afternoon with areas from Lincoln south mainly light rain and mix of
light rain/snow northern counties with little or no snow
accumulations during daytime hours Sat. Highs Sat in the lower 40s,
with upper 30s from I-74 north. Brunt of snow and moderate at times
to develop during Saturday night into Sunday with mix of rain/snow
sw counties Sat evening. Models have trended heavier with qpf close
to three quarter inches and snowfall amounts especially north of
I-70. NE winds to veer north and increase during day Sunday from nw
to se and temperatures will likely be slipping Sunday especially in
afternoon with some blowing snow developing by Sunday afternoon into
Sunday evening. Light snow to diminish from the west during Sunday
night as low pressure pulls away from IL.

Canadian high pressure drifts down into IL from western Canadian Rockies
by Monday afternoon returning dry but cold weather as skies become
partly to mostly sunny. Highs Monday only in upper teens and lower
20s Monday due to expected snow pack. Temps briefly climb Tue into
low to mid 30s with breezy ssw winds ahead of clipper system that
moves into Great Lakes region Tue night and swings a cold front se
through IL Wed bringing chances of light snow and flurries. Even
colder air to follow this weather system for from Wed night through
Friday with lows possibly getting below zero Thu night after highs
Thu in mid to upper teens over central IL with lower 20s south of
I-70.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
ISSUED AT 542 AM CST FRI JAN 30 2015

Mainly quiet/VFR aviation weather conditions expected across the
central Illinois terminals through the 12Z TAF valid time. Skies
have become mostly clear across much of the area in the past few
hours, and cloud cover through the remainder of the period is
expected to remain minimal. However, will have to monitor some of
the MVFR cigs that still exist upstream across the upper Midwest
and see if any of them can hold together as they stream this way.
Northwest winds will diminish early this morning, becoming
light/variable as high pressure builds into the area. Winds are
then expected to trend southerly tonight as the high pressure
ridge pushes east of the area.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Bak
LONG TERM...07
AVIATION...Bak







000
FXUS63 KILX 300929
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
329 AM CST Fri Jan 30 2015

.SHORT TERM...(Today)
ISSUED AT 329 AM CST FRI JAN 30 2015

High pressure will build across central and southeast Illinois today
from the northwest. This Canadian high will bring cooler air into
the area than yesterday, but the fact that winds will be much
lighter and at least partly sunny skies are anticipated should make
for a decent late January day. The only real wild card today from
what should be a quiet weather day is how much cloud cover there
will be. Skies across the area are rapidly clearing from the
northwest as the high builds in, but there are still significant
patches of clouds upstream beneath the ridge axis across the upper
Midwest. For now, plan to be optimistic with cloud cover given the
clearing that has taken place so far, and the fact that forecast
soundings do not suggest significant low level moisture trapped
beneath the subsidence inversion.

&&

.LONG TERM...(Tonight through Thursday)
ISSUED AT 329 AM CST FRI JAN 30 2015

00Z Jan 30th forecast model suite continues to trend further north
with ECMWF model the further north and much further north than its
model runs a few runs ago. Concensus of models has heaviest snow
band to set up over our northern counties north of a Springfield to
Paris line during Saturday night and Sunday where 6-8 inches of snow
and locally higher amounts possible. Between 3-5 inches of snow
south of I-70 in southeast IL