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000
FXUS63 KLOT 220318
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
918 PM CST SUN DEC 21 2014

.UPDATE...
914 PM CST

WHILE THERMAL PROFILES ARE STILL A BIT TRICKY IN OUR WESTERN CWA
OVERNIGHT...FEELING IS THAT IF SOME PRECIP SNEAKS IN OVERNIGHT...SURFACE
TEMPS WOULD BE AROUND FREEZING OR POSSIBLY SLIGHTLY WARMER WHICH
WOULD MITIGATE IMPACTS SIGNIFICANTLY.  MLI IS REPORTING UNKNOWN
PRECIP THIS EVENING BUT WITH A SURFACE TEMP IN THE MID 30S. WHEN
PRECIP ARRIVES IN THE MORNING IN THE WEST AND SOUTH...TEMPS SHOULD
LARGELY STILL BE ABOVE FREEZING. WHILE THE CHANCE IS NOT ZERO FOR
SOME LIGHT FZDZ OR SLEEET...CONFIDENCE IS LOW.

KMD

&&

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PRIMARILY VFR OR MVFR CIGS THROUGH MONDAY MORNING...LIKELY
  LOWERING TO IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY
  EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 220318
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
918 PM CST SUN DEC 21 2014

.UPDATE...
914 PM CST

WHILE THERMAL PROFILES ARE STILL A BIT TRICKY IN OUR WESTERN CWA
OVERNIGHT...FEELING IS THAT IF SOME PRECIP SNEAKS IN OVERNIGHT...SURFACE
TEMPS WOULD BE AROUND FREEZING OR POSSIBLY SLIGHTLY WARMER WHICH
WOULD MITIGATE IMPACTS SIGNIFICANTLY.  MLI IS REPORTING UNKNOWN
PRECIP THIS EVENING BUT WITH A SURFACE TEMP IN THE MID 30S. WHEN
PRECIP ARRIVES IN THE MORNING IN THE WEST AND SOUTH...TEMPS SHOULD
LARGELY STILL BE ABOVE FREEZING. WHILE THE CHANCE IS NOT ZERO FOR
SOME LIGHT FZDZ OR SLEEET...CONFIDENCE IS LOW.

KMD

&&

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PRIMARILY VFR OR MVFR CIGS THROUGH MONDAY MORNING...LIKELY
  LOWERING TO IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY
  EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 220314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
913 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PRIMARILY VFR OR MVFR CIGS THROUGH MONDAY MORNING...LIKELY
  LOWERING TO IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY
  EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS
UNTIL 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 220314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
913 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PRIMARILY VFR OR MVFR CIGS THROUGH MONDAY MORNING...LIKELY
  LOWERING TO IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY
  EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS
UNTIL 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 220313
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
913 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* PRIMARILY VFR OR MVFR CIGS THROUGH MONDAY MORNING...LIKELY
  LOWERING TO IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY
  EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI

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

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 220308
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
908 PM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 904 PM CST SUN DEC 21 2014

Moisture channel satellite imagery depicts minor vort max near
Quincy moving to the northeast. Radar showing development of some
very light pcpn ahead of the vort max over north central IL.
Updated the grids for sprinkles for few hours late this evening.
Clouds have come back into the region with the wave.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Goetsch
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch






000
FXUS63 KILX 220308
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
908 PM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 904 PM CST SUN DEC 21 2014

Moisture channel satellite imagery depicts minor vort max near
Quincy moving to the northeast. Radar showing development of some
very light pcpn ahead of the vort max over north central IL.
Updated the grids for sprinkles for few hours late this evening.
Clouds have come back into the region with the wave.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Goetsch
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch






000
FXUS63 KILX 220308
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
908 PM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 904 PM CST SUN DEC 21 2014

Moisture channel satellite imagery depicts minor vort max near
Quincy moving to the northeast. Radar showing development of some
very light pcpn ahead of the vort max over north central IL.
Updated the grids for sprinkles for few hours late this evening.
Clouds have come back into the region with the wave.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Goetsch
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch






000
FXUS63 KILX 220308
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
908 PM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 904 PM CST SUN DEC 21 2014

Moisture channel satellite imagery depicts minor vort max near
Quincy moving to the northeast. Radar showing development of some
very light pcpn ahead of the vort max over north central IL.
Updated the grids for sprinkles for few hours late this evening.
Clouds have come back into the region with the wave.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Goetsch
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch






000
FXUS63 KILX 212341
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
541 PM CST Sun Dec 21 2014

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch







000
FXUS63 KILX 212341
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
541 PM CST Sun Dec 21 2014

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch







000
FXUS63 KILX 212341
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
541 PM CST Sun Dec 21 2014

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch







000
FXUS63 KILX 212341
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
541 PM CST Sun Dec 21 2014

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.

&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
ISSUED AT 538 PM CST SUN DEC 21 2014

Not a lot of changes in the aviation trends. HRRR model continues
to show VFR cigs overnight and delayed the onset of the IFR cigs
in rain slightly tomorrow with the latest NAM model output. Model
soundings continue to show signficant pcpn development in the
morning. Lowered the vsb also by afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Goetsch







000
FXUS63 KLOT 212329
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
529 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

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

* PRIMARILY MVFR CIGS THROUGH MONDAY MORNING...LIKELY LOWERING TO
  IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI


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

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 212329
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
529 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

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

* PRIMARILY MVFR CIGS THROUGH MONDAY MORNING...LIKELY LOWERING TO
  IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI


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

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 212329
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
529 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

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

* PRIMARILY MVFR CIGS THROUGH MONDAY MORNING...LIKELY LOWERING TO
  IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI


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

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 212329
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
529 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

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

* PRIMARILY MVFR CIGS THROUGH MONDAY MORNING...LIKELY LOWERING TO
  IFR MONDAY AFTERNOON AND POSSIBLY LIFR MONDAY EVENING
* RAIN DEVELOPS AROUND MIDDAY MONDAY AND CONTINUES THROUGH MONDAY
  EVENING

IZZI

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

ANOTHER DAY OF STRATUS ACROSS THE REGION. SOUTHERN FLANK OF
STRATUS HAD BEEN LIFTING NORTH TOWARD I-80 BUT APPEARS TO BE
RECENTLY REDEVELOPING. CONFIDENCE IN CIGS TONIGHT IS LOW WITH MANY
MODELS SUGGESTING IMPROVEMENT TO VFR...THOUGH IN LIGHT OF RECENT
TRENDS HAVE OPTED TO RUN WITH MVFR WITH VERY LOW CONFIDENCE. RAIN
WILL LIKELY OVERSPREAD THE TERMINALS MIDDAY MONDAY AND CONTINUE
FAIRLY STEADILY INTO THE EVENING HOURS. CIGS/VSBY SHOULD FALL WITH
THE ONSET OF RAIN WITH IFR CONDITIONS LIKELY...PROBABLY LOWERING
TO LIFR MONDAY EVENING.

IZZI


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

* LOW CONFIDENCE IN CIGS TONIGHT/MONDAY MORNING INCREASING TO LOW-
  MEDIUM CONFIDENCE LATER MON AFTERNOON AND EVENING
* MEDIUM-HIGH CONFIDENCE IN GENERAL PRECIP TIMING
* HIGH CONFIDENCE IN REMAINING ELEMENTS

IZZI

//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...

TUESDAY...MVFR CIGS LIKELY. IFR CIGS POSSIBLE...MAINLY EARLY.

WEDNESDAY...MVFR CIGS LIKELY. CHANCE OF RA/SN.

THURSDAY...CHANCE OF MVFR CIGS...MAINLY EARLY.

FRIDAY...CHANCE OF MVFR CIGS. CHANCE OF -RA/-SN

SATURDAY...MVFR CIGS LIKELY. CHANCE OF FLURRIES.

IZZI

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 212208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR AND IFR MONDAY
* RAIN DEVELOPS MIDDAY MONDAY

IZZI

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW-MEDIUM CONFIDENCE IN CIGS TONIGHT AND MONDAY
  MORNING...MEDIUM CONFIDENCE IN CIGS MONDAY AFTERNOON
* HIGH CONFIDENCE IN WINDS
* MEDIUM-HIGH CONFIDENCE IN PRECIP TIMING.

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 212208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR AND IFR MONDAY
* RAIN DEVELOPS MIDDAY MONDAY

IZZI

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW-MEDIUM CONFIDENCE IN CIGS TONIGHT AND MONDAY
  MORNING...MEDIUM CONFIDENCE IN CIGS MONDAY AFTERNOON
* HIGH CONFIDENCE IN WINDS
* MEDIUM-HIGH CONFIDENCE IN PRECIP TIMING.

IZZI

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 212057
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
257 PM CST Sun Dec 21 2014

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.


&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.


&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1149 AM CST SUN DEC 21 2014

MVFR ceilings prevail at the KILX terminals late this morning:
however, the cloud cover is beginning to erode across east-central
Illinois. 1730z visible satellite imagery shows clearing line from
KPRG to just north of K1H2 and lifting slowly northward. Based on
timing tools and latest HRRR forecast, skies will partially clear
at KCMI between 20z and 21z. Further west, forecast soundings
suggest a continued MVFR overcast through the afternoon before
ceilings gradually improve to VFR this evening in advance of an
approaching storm system. IFR ceilings will develop/spread across
the area between 13z and 16z Mon as rain showers arrive from the
southwest. Winds will be from the S/SE at 10-5kt through the
entire period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Barnes







000
FXUS63 KILX 212057
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
257 PM CST Sun Dec 21 2014

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST SUN DEC 21 2014

Low pressure currently over southern Alberta will track into eastern
South Dakota by 12z Mon.  Ahead of the system, a tightening pressure
gradient will produce southeasterly winds of 10 to 15 mph across
central Illinois tonight.  Due to these sustained winds and a partly
to mostly cloudy sky, overnight low temperatures will be a few
degrees warmer than last night and several degrees warmer than
either the MAV or MET guidance.  Lows will once again be coolest
across the SE KILX CWA where skies will initially be mostly clear
and warmest across the W/NW where clouds will hold firm.  Readings
will range from the upper 20s near the Indiana border to the middle
30s along/west of I-55.  Any precipitation associated with the
approaching system will remain west of the Mississippi River until
later Monday morning, as forecast soundings remain dry through 12z.


&&

.LONG TERM...(Monday through Sunday)
ISSUED AT 256 PM CST SUN DEC 21 2014

Beginning to look like a good news/bad news scenario setting up with
the storm system expected to impact central and southeast Illinois
from Monday into Christmas Eve. If recent model trends hold, the
good news will be that significant weather related travel impacts
are not expected on Christmas Eve in the area. The bad news, for
some, would be that a "White Christmas" is looking less likely
locally.

We are still looking at active weather the next few days as a
complex, slow moving, storm system impacts the area. A 160+ kt
upper-level jet crashing into the Pacific NW & northern Rockies will
continue to amplify troffing over the middle of the nation, a trof
that will be with us for a few days.

A closed upper low is expected to develop over the northern
Plains/upper Midwest Monday, nearly vertically stacked with an
associated surface low. The WAA/isentropic lift ahead of these lows
will be accompanied by a periods of rainfall from Monday into Monday
night. Then, another vigorous piece of upper energy will round the
base of the mean trof Tuesday into Wednesday, accompanied by the
development of another surface low. This second low will become the
dominant low, with the first low expected to dissipate. A dry slot
is progged to wrap around the initial upper low, no doubt aided by
the secondary wave intercepting much of the deeper moisture. This
dry slot may result in much of Tuesday/Tuesday night ending up dry
across the northwest 1/2 of the forecast area, certainly drier than
it looked yesterday. The southeast 1/2 of the forecast area should
see rain chances persisting Tuesday and Tuesday night, as this area
will be closer to the track of the secondary wave. The remaining
precipitation will change over to light snow on Christmas Eve, but
model agreement is strengthening and this suggests that snowfall
will not be a significant impact across the forecast area.

Mostly dry conditions are expected by Christmas Day as the system
heads northeast into Canada. Another, much weaker, system is progged
to impact the area by Friday. However, guidance suggests that this
system will have minimal moisture to work with until it moves east
of the forecast area. This is because there will not have been much
time for the atmosphere to recover from the cold/dry advection in
the wake of the midweek system. So, only have a slight chance of
rain and/or snow for Friday into Friday night. While temperatures
will be above normal for much of this week, they will trend below
normal behind Friday`s system.


&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1149 AM CST SUN DEC 21 2014

MVFR ceilings prevail at the KILX terminals late this morning:
however, the cloud cover is beginning to erode across east-central
Illinois. 1730z visible satellite imagery shows clearing line from
KPRG to just north of K1H2 and lifting slowly northward. Based on
timing tools and latest HRRR forecast, skies will partially clear
at KCMI between 20z and 21z. Further west, forecast soundings
suggest a continued MVFR overcast through the afternoon before
ceilings gradually improve to VFR this evening in advance of an
approaching storm system. IFR ceilings will develop/spread across
the area between 13z and 16z Mon as rain showers arrive from the
southwest. Winds will be from the S/SE at 10-5kt through the
entire period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Barnes






000
FXUS63 KLOT 212048
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
248 PM CST SUN DEC 21 2014

.SHORT TERM...
246 PM CST

THROUGH TUESDAY...

TONIGHT THROUGH TUESDAY...
BROAD SFC RIDGE HAS BECOME CENTERED OVER THE NORTHEAST CONUS...AND
CONTINUES TO SLOWLY DRIFT EAST/NORTHEAST. THE GRADIENT ACROSS THE
GREAT LAKES HAS REMAINED LIGHT THIS AFTN...WITH A MAINLY SOUTHERLY
FLOW. CLOUDS REMAIN LOCKED IN ACROSS THE FORECAST AREA...WITH SOME
CLEARING JUST SOUTHEAST OF THE CWFA IN CENTRAL/NORTHERN IN. SFC
TEMPS HAVE BEEN ABLE TO WARM TO THE MID/UPR 30S...WITH DEW PTS
HOVERING AROUND 30-33 DEG. MOST THE EVENING WILL REMAIN DRY...WITH
THE WEAK MID-LVL WAVE SLIDING NORTHEAST ACROSS IOWA/WISC WITH SOME
LGT SNOW...OTHERWISE MOST OF THE FORECAST AREA SHUD REMAIN DRY THRU
THE OVERNIGHT PERIOD.

500MB VORT BEGINS TO LIFT NORTHEAST FROM THE CENTRAL PLAINS BEFORE
DAYBREAK MON...PUSHING THE MOIST CHANNEL FURTHER EAST ACROSS THE
FORECAST AREA. WITH SOUNDINGS SUGGESTING A WARM WEDGE DEVELOPING
ALOFT...P-TYPE COULD BE A CHALLENGE ARND DAYBREAK. GUIDANCE WOULD
SUGGEST TEMPS COULD BE WARM ENOUGH TO LIMIT PRECIP TO LGT
RAIN...WITH NEAR SFC TEMPS HOLDING ARND THE FREEZING MARK...SO HAVE
CONTINUED THE MENTION OF FZRA MAINLY SOUTH OF ROCKFORD. CLOSER TO
ROCKFORD THE THERMAL PROFILE IS A LITTLE MORE TRICKY AND COULD ALLOW
SOME LGT SNOW/SLEET AT THE ONSET CHANGING TO LGT RA/FZRA BEFORE
MIDDAY. THROUGHOUT THE AFTN TEMPS WILL STEADILY WARM...NEARING 40
DEG IN MOST LOCATIONS AS WARM/MOIST AIR CONTINUES TO ADVECT NORTH
ACROSS THE CWFA. MOST GUIDANCE INDICATES LGT RAIN WILL PERSIST THRU
THE AFTN/EVE HOURS...WITH THE DRY WEDGE NOT ARRIVING UNTIL CLOSER TO
DAYBREAK TUE. LOCAL SOLUTION SUGGESTS SLIGHTLY EARLIER WITH BRINGING
A TEMPORARY END TO THE PRECIP...JUST AFT MIDNIGHT MON NGT.

TEMPS OVERNIGHT WILL REMAIN MILD IN THE UPR 30S/NEAR 40. WITH THE
TROUGH TAKING ON A NEGATIVE TILT MIDDAY TUE...THE SFC LOW WILL BE
WRAPPED UP ACROSS CENTRAL WISC. GUIDANCE HAS BOUNCED AROUND POSSIBLY
KEEPING EITHER DRY/LOW CHC POPS OVER NORTHERN IL/NORTHWEST IN
TUE/TUE AFTN...BUT HAVE OPTED TO HOLD ONTO A SLT CHC OF RAIN. WITH
WARM AIR CONTINUING TO ADVECT NORTH...SFC TEMPS COULD PUSH INTO THE
MID/UPR 40S WITH A FEW LOCATIONS IN THE SOUTHEAST REACHING 50 DEG.
BY TUE EVENING THE TROUGH AXIS IS PROGGED TO EJECT ANOTHER SFC LOW
ACROSS THE GULF STATES...THEN QUICKLY LIFT NORTH ACROSS THE TENN
VALLEY LATE TUE NGT. MOISTURE WILL FILL BACK IN ACROSS THE FORECAST
AREA TUE NGT...WITH RAIN BECOMING MIXED WITH SNOW OVERNIGHT. TEMPS
WILL SLOWLY COOL...SO THE PERIOD OF RAIN/SNOW MIX COULD LINGER
AWHILE.

BEACHLER

&&

.LONG TERM...
246 PM CST

WEDNESDAY THROUGH SUNDAY...

MID-WEEK ENSEMBLES CONTINUE TO PROG A SLIGHT STRENGTHENING TO THE
DOWNSTREAM RIDGE OVER THE CANADIAN MARITIME...WHICH WILL LIMIT HOW
FAR EAST THE SECONDARY LOW WILL PROGRESS. OPERATIONAL SOLUTIONS
CONTINUE TO LIFT THE STRENGTHENING LOW NORTH ACROSS THE OHIO VALLEY
WED AFTN...AND QUICKLY NORTH OF LAKE HURON BY LATE WED NGT. WRAP
AROUND MOISTURE AND COOLER AIR WILL BRING SOME LGT SNOW TO NORTHERN
IL WED.

FOR CHRISTMAS DAY THE DOWNSTREAM RIDGE WILL BEGIN TO
WEAKEN...ALLOWING THE MID-LVL TROUGH TO BECOME PROGRESSIVE AND PUSH
EAST. THIS SHUD BRING AN END TO THE LGT SNOW/FLURRIES BY DAYBREAK.
TEMPS SHUD RETURN TO THE MID/UPR 30S...ALONG WITH PERHAPS SOME
BREAKS IN THE CLOUD COVER BY THE AFTN. MID-LVL HEIGHTS SHUD START TO
INCREASE THUR NGT/FRI...HOWEVER THIS LOOKS TO BE SHORT-LIVED AS YET
ANOTHER TROUGH IS PROGGED TO DIG SOUTH FROM THE CANADIAN ROCKIES
INTO THE NORTHERN PLAINS. THE STRONGER PUSH OF COLDER AIR LOOKS TO
ARRIVE SAT...ALTHOUGH THIS MAY ONLY BE A SHORT DURATION WITH THE
SEMI-ZONAL PATTERN SETTING UP FOR THE SECOND HALF OF THE WEEKEND.

BEACHLER

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW CONFIDENCE IN CIGS REST OF TODAY AND TONIGHT...MEDIUM
  CONFIDENCE IN CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ741-LMZ742...NOON MONDAY TO 3 AM
     TUESDAY.

&&

$$

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 212006
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
206 PM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW CONFIDENCE IN CIGS REST OF TODAY AND TONIGHT...MEDIUM
  CONFIDENCE IN CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
204 PM CST

SMALL CRAFT ADVISORY...KEPT THE CURRENT SMALL CRAFT AS IS AND
EXPANDED IT TWO ZONES SOUTH THROUGH CALUMET HARBOR.  WAVES WILL
BECOME HAZARDOUS OVERNIGHT NORTH OF WILMETTE HARBOR AND THEN WINDS
AND WAVES WILL BECOME HAZARDOUS TOMORROW AFTERNOON. MARGINAL SMALL
CRAFT CONDITIONS ARE POSSIBLE ALONG THE INDIANA NEARSHORE WATERS AND
DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE A SMALL CRAFT ADVISORY AT
THIS TIME.

HIGH PRESSURE IS OVER THE EAST COAST WHILE THE NEXT LOW IS OVER THE
NORTHERN PLAINS.  SOUTH WINDS HAVE INCREASED TO 15-25 KT ACROSS THE
LAKE AND WILL CONTINUE TO INCREASE TO 30 KT THIS AFTERNOON. WINDS
BECOME SOUTHEAST TOMORROW AS THE LOW MOVES OVER THE EASTERN PLAINS
AND WEAKENS.  THE LOW THEN WEAKENS OVER WISCONSIN TUESDAY AFTERNOON
THROUGH TUESDAY NIGHT. WINDS WEAKEN ACROSS THE LAKE MONDAY NIGHT AND
BECOME WEST TO NORTHWEST 10-15 KT TUESDAY NIGHT.  A SECOND LOW FORMS
OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY NIGHT AND QUICKLY
DEEPENS AS IT MOVES NORTH.  GUIDANCE DIFFERS ON HOW FAR TO OUR EAST
THE LOW WILL PASS...BUT THINKING IT WILL BE OVER THE EASTERN GREAT
LAKES. GUIDANCE HAS ALSO BACKED OFF ON WIND SPEEDS BEHIND THE LOW
AND WILL ONLY CARRY OCCASIONAL GALES IN THE GLF AT THIS TIME. SO
HAVE WEST TO NORTHWEST WINDS INCREASING TO 30 KT WEDNESDAY NIGHT.
THE BEST WINDOW FOR GALES WOULD BE LATE WEDNESDAY NIGHT.  THE LOW
THEN CONTINUES NORTHEAST INTO QUEBEC THURSDAY AND HAVE SOUTHWEST
WINDS DECREASING THURSDAY.  ANOTHER LOW SLIDES ACROSS THE PLAINS
THURSDAY AFTERNOON AND WILL IMPACT THE LAKE FRIDAY.  GUIDANCE
DIFFERS ON HOW STRONG THE LOW WILL BE WHEN IT MOVES OVER THE
LAKE...SO HAVE LOW CONFIDENCE IN THE FORECAST LATE NEXT WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
140 PM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW CONFIDENCE IN CIGS REST OF TODAY AND TONIGHT...MEDIUM
  CONFIDENCE IN CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
140 PM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW CONFIDENCE IN CIGS REST OF TODAY AND TONIGHT...MEDIUM
  CONFIDENCE IN CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
140 PM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW CONFIDENCE IN CIGS REST OF TODAY AND TONIGHT...MEDIUM
  CONFIDENCE IN CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211940
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
140 PM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD

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

* LOW CONFIDENCE IN CIGS REST OF TODAY AND TONIGHT...MEDIUM
  CONFIDENCE IN CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211749
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1149 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1149 AM CST SUN DEC 21 2014

MVFR ceilings prevail at the KILX terminals late this morning:
however, the cloud cover is beginning to erode across east-central
Illinois. 1730z visible satellite imagery shows clearing line from
KPRG to just north of K1H2 and lifting slowly northward. Based on
timing tools and latest HRRR forecast, skies will partially clear
at KCMI between 20z and 21z. Further west, forecast soundings
suggest a continued MVFR overcast through the afternoon before
ceilings gradually improve to VFR this evening in advance of an
approaching storm system. IFR ceilings will develop/spread across
the area between 13z and 16z Mon as rain showers arrive from the
southwest. Winds will be from the S/SE at 10-5kt through the
entire period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Barnes







000
FXUS63 KILX 211749
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1149 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1149 AM CST SUN DEC 21 2014

MVFR ceilings prevail at the KILX terminals late this morning:
however, the cloud cover is beginning to erode across east-central
Illinois. 1730z visible satellite imagery shows clearing line from
KPRG to just north of K1H2 and lifting slowly northward. Based on
timing tools and latest HRRR forecast, skies will partially clear
at KCMI between 20z and 21z. Further west, forecast soundings
suggest a continued MVFR overcast through the afternoon before
ceilings gradually improve to VFR this evening in advance of an
approaching storm system. IFR ceilings will develop/spread across
the area between 13z and 16z Mon as rain showers arrive from the
southwest. Winds will be from the S/SE at 10-5kt through the
entire period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Barnes







000
FXUS63 KILX 211749
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1149 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1149 AM CST SUN DEC 21 2014

MVFR ceilings prevail at the KILX terminals late this morning:
however, the cloud cover is beginning to erode across east-central
Illinois. 1730z visible satellite imagery shows clearing line from
KPRG to just north of K1H2 and lifting slowly northward. Based on
timing tools and latest HRRR forecast, skies will partially clear
at KCMI between 20z and 21z. Further west, forecast soundings
suggest a continued MVFR overcast through the afternoon before
ceilings gradually improve to VFR this evening in advance of an
approaching storm system. IFR ceilings will develop/spread across
the area between 13z and 16z Mon as rain showers arrive from the
southwest. Winds will be from the S/SE at 10-5kt through the
entire period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Barnes







000
FXUS63 KILX 211749
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1149 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1149 AM CST SUN DEC 21 2014

MVFR ceilings prevail at the KILX terminals late this morning:
however, the cloud cover is beginning to erode across east-central
Illinois. 1730z visible satellite imagery shows clearing line from
KPRG to just north of K1H2 and lifting slowly northward. Based on
timing tools and latest HRRR forecast, skies will partially clear
at KCMI between 20z and 21z. Further west, forecast soundings
suggest a continued MVFR overcast through the afternoon before
ceilings gradually improve to VFR this evening in advance of an
approaching storm system. IFR ceilings will develop/spread across
the area between 13z and 16z Mon as rain showers arrive from the
southwest. Winds will be from the S/SE at 10-5kt through the
entire period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Barnes







000
FXUS63 KLOT 211729
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1129 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD


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

* LOW CONFIDENCE IN CIGS TODAY AND TONIGHT...MEDIUM CONFIDENCE IN
  CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211729
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1129 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* PERIODS OF MVFR CIGS THROUGH TONIGHT...THEN INCREASING CHANCES
  FOR CIGS LOWERING TO IFR THROUGH THE AFTERNOON MONDAY.
* PRIMARILY RAIN OVERSPREADING TERMINALS MONDAY AFTERNOON...THOUGH
  A WINTRY MIX IS POSSIBLE NEAR THE ONSET.

BMD

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

LOW PRESSURE IS IN PLACE OVER THE NORTHERN ROCKIES THIS AFTERNOON
AND WILL MOVE ACROSS THE MID MISSOURI VALLEY OVERNIGHT WITH A WARM
FRONT LIFTING ACROSS ILLINOIS THROUGH THE DAY MONDAY. SOUTH WINDS
THIS AFTERNOON WILL TURN MORE SOUTHEASTERLY TONIGHT IN ADVANCE OF
THE FRONTAL BOUNDARY. MODELS HAVE LITTLE CONSISTENCY WITH RESPECT TO
CIG HEIGHTS...SO FOR NOW WILL MAINTAIN PREVIOUSLY ADVERTISED TRENDS
WITH SOME MODELS SHOWING SOME RECOVERY IN CIG HEIGHTS EARLY MONDAY.
HAVE MORE CONFIDENCE IN CIGS LOWERING AGAIN THROUGH THE AFTERNOON
MONDAY WITH IFR SEEMING LIKELY AS THE WARM FRONT LIFTS ACROSS THE
TERMINALS. PRECIP WILL OVERSPREAD THE REGION BY LATE MORNING OR
EARLY AFTERNOON. SOUNDINGS SHOW THE COLUMN COOL ENOUGH TO SUPPORT A
MIX OF RAIN AND SNOW INITIALLY BUT SHOULD FAIRLY QUICKLY WARM ENOUGH
TO BECOME ALL RAIN.

BMD


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

* LOW CONFIDENCE IN CIGS TODAY AND TONIGHT...MEDIUM CONFIDENCE IN
  CIGS LOWERING TO IFR MONDAY AFTERNOON.
* MEDIUM-HIGH CONFIDENCE IN WIND DIRECTION...MEDIUM IN SPEEDS.
* MEDIUM CONFIDENCE IN PRECIP TIMING. LOW-MEDIUM IN PRECIP TYPE
  INITIALLY BUT HIGH CONFIDENCE IN EVENTUALLY BECOMING ALL RAIN.

BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211635
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1035 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 535 AM CST SUN DEC 21 2014

MVFR to low VFR cigs expected today with high resolution model
data indicating the potential for the lower cigs to scatter
out at CMI and DEC later this morning into this afternoon.
In addition, some patchy fog and haze was bringing vsbys down
to MVFR as well but expect that to lift after 15z. Low level
southerly flow is expected to continue through tonight which
may effectively lower cigs back to lower MVFR again after 06z
but models have kept that scenario to our west later tonight
but will monitor for that possibility at PIA and SPI after
06z. Surface winds will be southeast to south today at 10 to
15 kts and then winds will tend to back more into a southeast
direction tonight at 8 to 13 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith






000
FXUS63 KILX 211635
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1035 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 535 AM CST SUN DEC 21 2014

MVFR to low VFR cigs expected today with high resolution model
data indicating the potential for the lower cigs to scatter
out at CMI and DEC later this morning into this afternoon.
In addition, some patchy fog and haze was bringing vsbys down
to MVFR as well but expect that to lift after 15z. Low level
southerly flow is expected to continue through tonight which
may effectively lower cigs back to lower MVFR again after 06z
but models have kept that scenario to our west later tonight
but will monitor for that possibility at PIA and SPI after
06z. Surface winds will be southeast to south today at 10 to
15 kts and then winds will tend to back more into a southeast
direction tonight at 8 to 13 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith






000
FXUS63 KILX 211635
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1035 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 535 AM CST SUN DEC 21 2014

MVFR to low VFR cigs expected today with high resolution model
data indicating the potential for the lower cigs to scatter
out at CMI and DEC later this morning into this afternoon.
In addition, some patchy fog and haze was bringing vsbys down
to MVFR as well but expect that to lift after 15z. Low level
southerly flow is expected to continue through tonight which
may effectively lower cigs back to lower MVFR again after 06z
but models have kept that scenario to our west later tonight
but will monitor for that possibility at PIA and SPI after
06z. Surface winds will be southeast to south today at 10 to
15 kts and then winds will tend to back more into a southeast
direction tonight at 8 to 13 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith






000
FXUS63 KILX 211635
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1035 AM CST Sun Dec 21 2014

.UPDATE...
ISSUED AT 1035 AM CST SUN DEC 21 2014

16z/10am visible satellite imagery shows cloud cover blanketing
much of central Illinois: however, skies remain mostly clear along
and south of the I-70 corridor into the Ohio River Valley.
Short-wave ridging in advance of an upper-level disturbance over
the Central Plains will allow heights to slowly rise today.
This along with continued backed southeasterly low-level flow will
cause the leading edge of the cloud cover to erode
north/northwestward this afternoon. Am already beginning to see
evidence of this on satellite this morning, so have updated sky
grids accordingly. End result will be mostly sunny skies
along/south of I-70, with skies becoming partly sunny as far
northwest as a Shelbyville to Champaign line. Further west, mostly
cloudy conditions will prevail across the remainder of the area.
High temperatures will be a few degrees warmer than yesterday,
with readings reaching the upper 30s and lower 40s.

&&

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 535 AM CST SUN DEC 21 2014

MVFR to low VFR cigs expected today with high resolution model
data indicating the potential for the lower cigs to scatter
out at CMI and DEC later this morning into this afternoon.
In addition, some patchy fog and haze was bringing vsbys down
to MVFR as well but expect that to lift after 15z. Low level
southerly flow is expected to continue through tonight which
may effectively lower cigs back to lower MVFR again after 06z
but models have kept that scenario to our west later tonight
but will monitor for that possibility at PIA and SPI after
06z. Surface winds will be southeast to south today at 10 to
15 kts and then winds will tend to back more into a southeast
direction tonight at 8 to 13 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith






000
FXUS63 KLOT 211613
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1013 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* S/SSE WINDS 10-15 KT...BECOMING SE LATER TONIGHT. A FEW GUSTS
  OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211613
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1013 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* S/SSE WINDS 10-15 KT...BECOMING SE LATER TONIGHT. A FEW GUSTS
  OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211613
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1013 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* S/SSE WINDS 10-15 KT...BECOMING SE LATER TONIGHT. A FEW GUSTS
  OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211613
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1013 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* S/SSE WINDS 10-15 KT...BECOMING SE LATER TONIGHT. A FEW GUSTS
  OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
804 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
804 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
804 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
804 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
804 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211404
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
804 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER/BMD

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER/BMD

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211223
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
623 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211223
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
623 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211223
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
623 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211223
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
623 AM CST SUN DEC 21 2014

.SHORT TERM...
620 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDITIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

&&

.LONG TERM...
620 AM CST

TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER

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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSIBLE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SUN DEC 21 2014

.SHORT TERM...
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.LONG TERM...
FXUS63 KLOT 210925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN DEC 21 2014

.SHORT TERM...THROUGH TUESDAY.
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER


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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.


RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSBILE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SUN DEC 21 2014

.SHORT TERM...
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.LONG TERM...
FXUS63 KLOT 210925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN DEC 21 2014

.SHORT TERM...THROUGH TUESDAY.
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER


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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.


RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSBILE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SUN DEC 21 2014

.SHORT TERM...
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.LONG TERM...
FXUS63 KLOT 210925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN DEC 21 2014

.SHORT TERM...THROUGH TUESDAY.
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER


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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.


RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSBILE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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

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






000
FXUS63 KLOT 211152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SUN DEC 21 2014

.SHORT TERM...
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.LONG TERM...
FXUS63 KLOT 210925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN DEC 21 2014

.SHORT TERM...THROUGH TUESDAY.
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER


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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.


RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSBILE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SUN DEC 21 2014

.SHORT TERM...
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.LONG TERM...
FXUS63 KLOT 210925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN DEC 21 2014

.SHORT TERM...THROUGH TUESDAY.
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER


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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.


RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSBILE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211152
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
552 AM CST SUN DEC 21 2014

.SHORT TERM...
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.LONG TERM...
FXUS63 KLOT 210925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN DEC 21 2014

.SHORT TERM...THROUGH TUESDAY.
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.

LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

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

* VERY LIGHT SNIZZLE/MVFR HZ/BR EARLY THIS MORNING.

* VFR CEILINGS LIKELY LOWERING TO MVFR BY AFTN AND CONTINUING
  TONIGHT.

* SSE WINDS INCREASING 10-15 KT BY MIDDAY...BECOMING SE LATER
  TONIGHT. A FEW GUSTS OVER 15 KT POSSIBLE THIS AFTN.

RATZER

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

SOUTHWEST FLOW JUST ABOVE THE SURFACE BRINGING INCREASED LOW LEVEL
MOISTURE INTO THE AREA. EXTENSIVE MVFR/IFR AND LIFR CIGS TO THE
WEST AND SOUTHWEST...THOUGH LOWER CIGS MORE PATCHY ACROSS NORTHERN
IL/IN TERMINALS. WEAK MID-LEVEL DISTURBANCE PASSING EARLY THIS AM
PRODUCING SOME VERY LIGHT --SN/--DZ WITH SOME MVFR VIS IN HZ/BR
BUT SHOULD BE OF RELATIVELY LITTLE IMPACT. OTHERWISE...IMMEDIATE
UPSTREAM SURFACE OBS MAINLY VFR CIGS IN 3000-4000 FT RANGE. MVFR
CIGS IN 2000-2500 FT RANGE ACROSS MISSOURI AND WESTERN IL THEN
EXPECTED TO MOVE IN DURING THE LATE MORNING/MIDDAY HOURS. LOW
PRESSURE OVER THE NORTHERN PLAINS TONIGHT WILL BACK WINDS A
BIT...WITH MODEL TRENDS SUPPORTING IMPROVEMENT TO VFR AT SOME
POINT...THOUGH CONFIDENCE LOWERS WITH EXTENSIVE UPSTREAM LOWER
CLOUDS.

SOUTH WINDS NEAR 10 KT EXPECTED TO INCREASE INTO 10-15 KT RANGE BY
MIDDAY...WITH SOME SPORADIC GUSTS ABOVE 15 KT POSSIBLE THIS
AFTERNOON THOUGH NOT FREQUENT. WINDS BACK MORE SOUTHEAST LATER
TONIGHT INTO MONDAY MORNING...INCREASING AFTER SUNRISE.

RATZER


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

* MEDIUM IN LIGHT PCPN AND CEILING TRENDS.

* MEDIUM-HIGH IN WINDS.


RATZER

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...RAIN. MVFR/IFR LIKELY. S-SE WINDS.

TUESDAY...CHANCE OF RAIN AND MVFR/IFR ESPECIALLY EARLY. S-SW WINDS.

WEDNESDAY...CHANCE OF SNOW...POSSIBLY MIXED WITH RAIN EARLY.
MVFR/IFR LIKELY. NW WINDS BECOMING W.

THURSDAY...DRY. MVFR CIGS POSSBILE EARLY. W WINDS BECOMING SW.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. S WINDS BECOMING W.

SATURDAY...DRY. MAINLY VFR. W WINDS.

RATZER

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 211141
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
541 AM CST Sun Dec 21 2014

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.


&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.


&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 535 AM CST SUN DEC 21 2014

MVFR to low VFR cigs expected today with high resolution model
data indicating the potential for the lower cigs to scatter
out at CMI and DEC later this morning into this afternoon.
In addition, some patchy fog and haze was bringing vsbys down
to MVFR as well but expect that to lift after 15z. Low level
southerly flow is expected to continue through tonight which
may effectively lower cigs back to lower MVFR again after 06z
but models have kept that scenario to our west later tonight
but will monitor for that possibility at PIA and SPI after
06z. Surface winds will be southeast to south today at 10 to
15 kts and then winds will tend to back more into a southeast
direction tonight at 8 to 13 kts.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith




000
FXUS63 KILX 211141
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
541 AM CST Sun Dec 21 2014

.SHORT TERM...(Today)
ISSUED AT 537 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.


&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 537 AM CST SUN DEC 21 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.


&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 535 AM CST SUN DEC 21 2014

MVFR to low VFR cigs expected today with high resolution model
data indicating the potential for the lower cigs to scatter
out at CMI and DEC later this morning into this afternoon.
In addition, some patchy fog and haze was bringing vsbys down
to MVFR as well but expect that to lift after 15z. Low level
southerly flow is expected to continue through tonight which
may effectively lower cigs back to lower MVFR again after 06z
but models have kept that scenario to our west later tonight
but will monitor for that possibility at PIA and SPI after
06z. Surface winds will be southeast to south today at 10 to
15 kts and then winds will tend to back more into a southeast
direction tonight at 8 to 13 kts.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith





000
FXUS63 KILX 210931
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
331 AM CST Sun Dec 21 2014

.SHORT TERM...(Today)
ISSUED AT 330 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Sunday)
ISSUED AT 330 AM CST SUN DEC 21 2014

Dry weather expected yet tonight as light rain chances stay west
of central IL until after daybreak Monday. Lows to range from
around 30F in eastern IL to mid 30s over western IL. Storm system
over the Pacific NW to track low pressure around 1000 mb or deeper
to near the SD/MN/IA border by sunset Mon, then weaken as it tracks
into the upper MS river valley on Tue. This will spread rain
showers east across IL during Monday with highest chances Monday
night and then highest rain chances shifting into southeast IL Tue
while diminishing to slight chances nw of IL river on Tue. Milder
temps in the mid to upper 40s expected Monday and Tue with even
50s over southeast IL Tue. LWV highs Tue is 56F MAV and 59F MET.

Forecast models still not in the best agreement with track and
development of southern low pressure system from Texas into the
ohio river valley and central Great Lakes region during mid week.
Models overall have trended slower with change over of rain to
snow and also GFS has trended further east with storm system,
with lighter snowfall accumulations overnight Tue night into Wed.
Have pops increasing again Tue night and Wed with highest pops/qpf
over eastern IL. Windy conditions expected Wed and Wed night as
colder air ushers in with temps back in the 30s on Wed.

Christmas day still looks dry as deepening low pressure pushes
into eastern Canada and surface ridge sets up over the southeast
states. Highs Thu in the upper 30s, to near 40F sw areas. Still
plenty of differences with forecast models with handling late week
storm system but trends have been lighter qpf Fri and Fri night.
Have lowered pops and have mainly light rain chances Fri with highs
upper 30s nw and mid 40s southeast IL. Then small chances of light
snow Fri night. Dry weather next weekend with cooler highs in the
upper 20s to mid 30s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1137 PM CST SAT DEC 20 2014

Cloudy skies will continue at all sites next 24hrs. Cigs are
hovering around 3kft with PIA and SPI above 3kft and BMI, DEC, and
CMI below. So will just have 3kft cigs at all sites since PIA and
SPI will likely drop below 3kft sometime overnight. Based on model
soundings and RH fields, am thinking the MVFR cigs will continue
through tomorrow and tomorrow night. Winds will be south-southeast
through the period, with speeds increase to around 10kts tomorrow
afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Auten







000
FXUS63 KILX 210931
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
331 AM CST Sun Dec 21 2014

.SHORT TERM...(Today)
ISSUED AT 330 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Sunday)
ISSUED AT 330 AM CST SUN DEC 21 2014

Dry weather expected yet tonight as light rain chances stay west
of central IL until after daybreak Monday. Lows to range from
around 30F in eastern IL to mid 30s over western IL. Storm system
over the Pacific NW to track low pressure around 1000 mb or deeper
to near the SD/MN/IA border by sunset Mon, then weaken as it tracks
into the upper MS river valley on Tue. This will spread rain
showers east across IL during Monday with highest chances Monday
night and then highest rain chances shifting into southeast IL Tue
while diminishing to slight chances nw of IL river on Tue. Milder
temps in the mid to upper 40s expected Monday and Tue with even
50s over southeast IL Tue. LWV highs Tue is 56F MAV and 59F MET.

Forecast models still not in the best agreement with track and
development of southern low pressure system from Texas into the
ohio river valley and central Great Lakes region during mid week.
Models overall have trended slower with change over of rain to
snow and also GFS has trended further east with storm system,
with lighter snowfall accumulations overnight Tue night into Wed.
Have pops increasing again Tue night and Wed with highest pops/qpf
over eastern IL. Windy conditions expected Wed and Wed night as
colder air ushers in with temps back in the 30s on Wed.

Christmas day still looks dry as deepening low pressure pushes
into eastern Canada and surface ridge sets up over the southeast
states. Highs Thu in the upper 30s, to near 40F sw areas. Still
plenty of differences with forecast models with handling late week
storm system but trends have been lighter qpf Fri and Fri night.
Have lowered pops and have mainly light rain chances Fri with highs
upper 30s nw and mid 40s southeast IL. Then small chances of light
snow Fri night. Dry weather next weekend with cooler highs in the
upper 20s to mid 30s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1137 PM CST SAT DEC 20 2014

Cloudy skies will continue at all sites next 24hrs. Cigs are
hovering around 3kft with PIA and SPI above 3kft and BMI, DEC, and
CMI below. So will just have 3kft cigs at all sites since PIA and
SPI will likely drop below 3kft sometime overnight. Based on model
soundings and RH fields, am thinking the MVFR cigs will continue
through tomorrow and tomorrow night. Winds will be south-southeast
through the period, with speeds increase to around 10kts tomorrow
afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Auten







000
FXUS63 KILX 210931
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
331 AM CST Sun Dec 21 2014

.SHORT TERM...(Today)
ISSUED AT 330 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Sunday)
ISSUED AT 330 AM CST SUN DEC 21 2014

Dry weather expected yet tonight as light rain chances stay west
of central IL until after daybreak Monday. Lows to range from
around 30F in eastern IL to mid 30s over western IL. Storm system
over the Pacific NW to track low pressure around 1000 mb or deeper
to near the SD/MN/IA border by sunset Mon, then weaken as it tracks
into the upper MS river valley on Tue. This will spread rain
showers east across IL during Monday with highest chances Monday
night and then highest rain chances shifting into southeast IL Tue
while diminishing to slight chances nw of IL river on Tue. Milder
temps in the mid to upper 40s expected Monday and Tue with even
50s over southeast IL Tue. LWV highs Tue is 56F MAV and 59F MET.

Forecast models still not in the best agreement with track and
development of southern low pressure system from Texas into the
ohio river valley and central Great Lakes region during mid week.
Models overall have trended slower with change over of rain to
snow and also GFS has trended further east with storm system,
with lighter snowfall accumulations overnight Tue night into Wed.
Have pops increasing again Tue night and Wed with highest pops/qpf
over eastern IL. Windy conditions expected Wed and Wed night as
colder air ushers in with temps back in the 30s on Wed.

Christmas day still looks dry as deepening low pressure pushes
into eastern Canada and surface ridge sets up over the southeast
states. Highs Thu in the upper 30s, to near 40F sw areas. Still
plenty of differences with forecast models with handling late week
storm system but trends have been lighter qpf Fri and Fri night.
Have lowered pops and have mainly light rain chances Fri with highs
upper 30s nw and mid 40s southeast IL. Then small chances of light
snow Fri night. Dry weather next weekend with cooler highs in the
upper 20s to mid 30s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1137 PM CST SAT DEC 20 2014

Cloudy skies will continue at all sites next 24hrs. Cigs are
hovering around 3kft with PIA and SPI above 3kft and BMI, DEC, and
CMI below. So will just have 3kft cigs at all sites since PIA and
SPI will likely drop below 3kft sometime overnight. Based on model
soundings and RH fields, am thinking the MVFR cigs will continue
through tomorrow and tomorrow night. Winds will be south-southeast
through the period, with speeds increase to around 10kts tomorrow
afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Auten







000
FXUS63 KILX 210931
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
331 AM CST Sun Dec 21 2014

.SHORT TERM...(Today)
ISSUED AT 330 AM CST SUN DEC 21 2014

All but extreme southeast Illinois was cloudy early this morning and
the latest satellite trends suggest the southeast may see the clouds
move in for a brief time over the next couple of hours. With the
clear sky, a few locations in southeast Illinois have seen some
patchy fog develop, but with the clouds starting to move in we don`t
expect the fog to become widespread. Further to the northwest, some
patchy drizzle has been occurring over parts of extreme eastern Iowa
and some of that, at least based on radar, was tracking into areas
mainly along and west of the Illinois River, so will carry some
patchy drizzle wording for early this morning before that shifts to
our north. Surface temperatures have risen into the middle 30s early
this morning along with dew points now into the lower 30s, so am not
expecting any problems from freezing drizzle at this point.

The slow moving high pressure system that had given parts of our
area some sunshine the past couple of days was finally drifting off
to our east allowing a southerly flow to develop over most of the
forecast area. Forecast soundings indicate our southeast counties
may see the lower cloud cover drift north-northeast out of their
area this morning allowing some sun for a time today. Further north
and west, short range models not as optimistic with a mostly cloudy
sky prevailing. We should see the temperatures continue to moderate
from the highs of yesterday with most areas close to or above the 40
degree mark this afternoon.

&&

.LONG TERM...(Tonight through Sunday)
ISSUED AT 330 AM CST SUN DEC 21 2014

Dry weather expected yet tonight as light rain chances stay west
of central IL until after daybreak Monday. Lows to range from
around 30F in eastern IL to mid 30s over western IL. Storm system
over the Pacific NW to track low pressure around 1000 mb or deeper
to near the SD/MN/IA border by sunset Mon, then weaken as it tracks
into the upper MS river valley on Tue. This will spread rain
showers east across IL during Monday with highest chances Monday
night and then highest rain chances shifting into southeast IL Tue
while diminishing to slight chances nw of IL river on Tue. Milder
temps in the mid to upper 40s expected Monday and Tue with even
50s over southeast IL Tue. LWV highs Tue is 56F MAV and 59F MET.

Forecast models still not in the best agreement with track and
development of southern low pressure system from Texas into the
ohio river valley and central Great Lakes region during mid week.
Models overall have trended slower with change over of rain to
snow and also GFS has trended further east with storm system,
with lighter snowfall accumulations overnight Tue night into Wed.
Have pops increasing again Tue night and Wed with highest pops/qpf
over eastern IL. Windy conditions expected Wed and Wed night as
colder air ushers in with temps back in the 30s on Wed.

Christmas day still looks dry as deepening low pressure pushes
into eastern Canada and surface ridge sets up over the southeast
states. Highs Thu in the upper 30s, to near 40F sw areas. Still
plenty of differences with forecast models with handling late week
storm system but trends have been lighter qpf Fri and Fri night.
Have lowered pops and have mainly light rain chances Fri with highs
upper 30s nw and mid 40s southeast IL. Then small chances of light
snow Fri night. Dry weather next weekend with cooler highs in the
upper 20s to mid 30s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1137 PM CST SAT DEC 20 2014

Cloudy skies will continue at all sites next 24hrs. Cigs are
hovering around 3kft with PIA and SPI above 3kft and BMI, DEC, and
CMI below. So will just have 3kft cigs at all sites since PIA and
SPI will likely drop below 3kft sometime overnight. Based on model
soundings and RH fields, am thinking the MVFR cigs will continue
through tomorrow and tomorrow night. Winds will be south-southeast
through the period, with speeds increase to around 10kts tomorrow
afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Auten







000
FXUS63 KLOT 210925
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN DEC 21 2014

.SHORT TERM...THROUGH TUESDAY.
320 AM CST

THE MAIN CONCERNS DURING THIS PERIOD WILL MAINLY BE FOCUSED ON
THE TIMING OF RAINFALL EXPECTED MONDAY AND MONDAY NIGHT.

WARM AIR ADVECTION/ISENTROPIC ASCENT HAS PRODUCED SOME DRIZZLE AND
EVEN SOME OCCASIONAL LIGHT SNOW/FLURRIES ACROSS PORTIONS OF NORTH
CENTRAL ILLINOIS EARLY THIS MORNING. TEMPERATURES ACROSS THE AREA
CONTINUE TO HOLD STEADY EITHER RIGHT AT FREEZING OR A DEGREE OR TWO
BELOW IN SOME AREAS. THEREFORE...THERE WILL CONTINUE TO BE THREAT
FOR SOME MINOR GLAZING ON UNTREATED SURFACES ACROSS PORTIONS OF
NORTH CENTRAL ILLINOIS THROUGH AROUND DAYBREAK.
THEREAFTER...TEMPERATURES SHOULD WARM ABOVE FREEZING...ESSENTIALLY
ENDING THIS THREAT. ASIDE FROM SOME LINGERING PATCHY DRIZZLE THIS
MORNING MOST AREAS WILL BE CLOUDY AGAIN...BUT DRY AS TEMPERATURES
WARM INTO THE UPPER 30S THIS AFTERNOON.

MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT THROUGH
TUESDAY...WITH AN INITIAL AREA OF LOW PRESSURE TRACKING EASTWARD
FROM THE NORTHERN HIGH PLAINS LATER TODAY...TO THE UPPER MISSISSIPPI
VALLEY BY TUESDAY. THIS STILL WOULD KEEP ALL OF NORTHERN
ILLINOIS/NORTHWESTERN INDIANA IN THE WARM SECTOR THROUGH TUESDAY. IT
THIS SYSTEM LOOKS TO BE A DECENT RAINFALL PRODUCER FOR MUCH OF THE
AREA...WITH THE BEST TIMING BEING MONDAY AFTERNOON THROUGH LATE
MONDAY NIGHT/EARLY TUESDAY MORNING. SEVERAL UPPER LEVEL SHORT WAVE
DISTURBANCES ROTATING THROUGH THE LARGER SCALE UPPER LOW OVER THE
PLAINS...SHOULD RESULT IN WHAT APPEARS TO BE TWO ROUNDS OF
RAINFALL...WITH THE FIRST AROUND THE MONDAY AFTERNOON
TIMEFRAME...AND THE SECOND MONDAY NIGHT. THERE IS A SMALL CHANCE
THAT AS THE PRECIPITATION ONSETS LATE MONDAY MORNING...THAT IT COULD
START AS A MIX OF SLEET AND LIGHT SNOW...GIVEN THE INITIAL COOL
ATMOSPHERIC PROFILE. HOWEVER...WARM AIR ADVECTION WILL QUICKLY WARM
THINGS ENOUGH TO RESULT IN ALL RAIN AREA-WIDE BY EARLY MONDAY
AFTERNOON.

DURING THE DAY ON TUESDAY IT APPEARS THAT WE MAY EXPERIENCE A MID
LEVEL DRY PUNCH...WHICH IF DOES OCCUR WOULD RESULT IN LOW CLOUDS
AND PERHAPS SOME LINGERING DRIZZLE AND LOWER CHANCES OF MUCH
ADDIONAL RAIN. GIVEN THIS...I HAVE LOWERED POPS A BIT DURING THE DAY
ON TUESDAY. TEMPERATURES ACROSS THE AREA MONDAY NIGHT AND TUESDAY
AS WE REMAIN IN THE WARM SECTOR LOOK TO BE MILD FOR THIS TIME OF
YEAR...WITH 40S EXPECTED.


LONG TERM...TUESDAY NIGHT THROUGH SATURDAY...

FORECAST MODEL SOLUTIONS CONCERNING THE EVOLUTION OF THE SURFACE AND
UPPER LEVEL PATTERN ACROSS THE CENTRAL CONUS FROM TUESDAY NIGHT
THROUGH CHRISTMAS HAVE BECOME MORE DIVERGENT OVER THE PAST COUPLE
RUNS...WITH SEVERAL SOLUTIONS EVEN NOW INDICATING THE POSSIBILITY
OF A MUCH WEAKER SURFACE SYSTEM OVER THE GREAT LAKES INTO
CHRISTMAS EVE DUE TO THE FAILURE OF THE UPPER LEVEL TROUGH
BECOMING NEGATIVELY TILTED OVER THE MISSISSIPPI VALLEY...AS MANY
MODELS HAD BEEN PREVIOUSLY ADVERTISING. HOWEVER...GIVEN THIS
SYSTEM IS STILL 3.5 TO 4 DAYS AWAY...I AM HESITANT TO MAKE ANY
MAJOR CHANGES TO THE GOING FORECAST FOR THIS PERIOD...AS IT
APPEARS THE LATEST DETERMINISTIC MODEL SOLUTIONS ARE REALLY JUST
SHOWING US THE INHERENT HIGH AMOUNT OF CHAOS IN THE SYSTEM WITH
SUCH A RAPIDLY CHANGING PATTERN. AS SUCH...I REALLY HAVE NO
CONFIDENCE IN ANY OF THE LATEST 00 UTC DETERMINISTIC GUIDANCE AND
WOULD PREFER TO SEE ADDITIONAL RUNS OVER THE NEXT DAY OR TWO SHOW
SIMILAR TRENDS BEFORE BEGINNING TO MAKING ANY BIG CHANGES. MY
HUNCH IS WE WILL CONTINUE TO SEE ADJUSTMENTS IN THE DETERMINISTIC
RUNS OVER THE NEXT COUPLE OF DAYS AS THE MODELS ATTEMPT TO RESOLVE
THE EVOLUTION OF THE UPPER LEVEL PATTERN OVER THE CENTRAL CONUS.

FOLLOWING THIS SYSTEM...MODEL GUIDANCE IS INDICATING ANOTHER
DISTURBANCE DIGGING ACROSS THE PLAINS STATE BY THURSDAY...AND THIS
COULD RESULT IN ANOTHER PERIOD OF PRECIPITATION ACROSS PORTIONS OF
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT FIRST.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 09Z...

AREA OF MVFR CIGS HAS MOVED ACROSS CHICAGO TERMINALS...THOUGH
SURFACE OBS UPSTREAM TO THE SOUTHWEST INDICATE CIGS RISING BACK TO
VFR AND EXPECT THIS TREND TO CONTIUE FOR THE NEXT FEW HOURS. MORE
SOLID MVFR CIG/VIS AND DZ/FZDZ JUST OFF TO THE WEST/NORTHWEST
INCLUDING KRFD.

RATZER

PREVIOUS DISCUSSION FROM 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-LOW CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210910
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
310 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 09Z...

AREA OF MVFR CIGS HAS MOVED ACROSS CHICAGO TERMINALS...THOUGH
SURFACE OBS UPSTREAM TO THE SOUTHWEST INDICATE CIGS RISING BACK TO
VFR AND EXPECT THIS TREND TO CONTIUE FOR THE NEXT FEW HOURS. MORE
SOLID MVFR CIG/VIS AND DZ/FZDZ JUST OFF TO THE WEST/NORTHWEST
INCLUDING KRFD.

RATZER

PREVIOUS DISCUSSION FROM 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-LOW CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210910
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
310 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 09Z...

AREA OF MVFR CIGS HAS MOVED ACROSS CHICAGO TERMINALS...THOUGH
SURFACE OBS UPSTREAM TO THE SOUTHWEST INDICATE CIGS RISING BACK TO
VFR AND EXPECT THIS TREND TO CONTIUE FOR THE NEXT FEW HOURS. MORE
SOLID MVFR CIG/VIS AND DZ/FZDZ JUST OFF TO THE WEST/NORTHWEST
INCLUDING KRFD.

RATZER

PREVIOUS DISCUSSION FROM 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-LOW CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210910
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
310 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 09Z...

AREA OF MVFR CIGS HAS MOVED ACROSS CHICAGO TERMINALS...THOUGH
SURFACE OBS UPSTREAM TO THE SOUTHWEST INDICATE CIGS RISING BACK TO
VFR AND EXPECT THIS TREND TO CONTIUE FOR THE NEXT FEW HOURS. MORE
SOLID MVFR CIG/VIS AND DZ/FZDZ JUST OFF TO THE WEST/NORTHWEST
INCLUDING KRFD.

RATZER

PREVIOUS DISCUSSION FROM 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-LOW CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210910
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
310 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 09Z...

AREA OF MVFR CIGS HAS MOVED ACROSS CHICAGO TERMINALS...THOUGH
SURFACE OBS UPSTREAM TO THE SOUTHWEST INDICATE CIGS RISING BACK TO
VFR AND EXPECT THIS TREND TO CONTIUE FOR THE NEXT FEW HOURS. MORE
SOLID MVFR CIG/VIS AND DZ/FZDZ JUST OFF TO THE WEST/NORTHWEST
INCLUDING KRFD.

RATZER

PREVIOUS DISCUSSION FROM 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM-LOW CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210841
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
241 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210841
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
241 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210841
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
241 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210841
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
241 AM CST SUN DEC 21 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
240 AM CST

MAIN MARINE CONCERNS CONTINUE TO FOCUS ON STRENGTHENING
SOUTH-SOUTHEAST WINDS TODAY THROUGH LATE MONDAY...AND POTENTIAL FOR
GUSTY NORTHWEST-WEST WINDS...POSSIBLY GALES...FROM LATE WEDNESDAY
INTO THURSDAY.

SURFACE HIGH PRESSURE RIDGE MOVED EAST OF THE LAKE ON SATURDAY
ALLOWING WINDS TO BECOME SOUTHERLY. THE SURFACE PRESSURE GRADIENT
WILL SLOWLY TIGHTEN ACROSS THE UPPER MIDWEST AND WESTERN LAKES TODAY
AS AN AREA OF LOW PRESSURE MOVES SOUTHEAST FROM THE LEE OF THE
CANADIAN ROCKIES...WITH SOUTH-SOUTHEAST WINDS INCREASING INTO THE
25-30 KT RANGE FROM LATER THIS AFTERNOON INTO MONDAY AS THE LOW
APPROACHES FROM THE NORTHERN PLAINS. THE IS EXPECTED TO OCCLUDE AND
BEING TO FILL LATE MONDAY NIGHT...ALLOWING THE GRADIENT TO WEAKEN
AND WINDS TO DIMINISH EARLY TUESDAY. THE REMNANT SURFACE TROUGH WILL
CROSS THE LAKE LATE TUESDAY NIGHT OR EARLY WEDNESDAY...WITH LIGHT
WINDS SHIFTING TO THE WEST-NORTHWEST.

FORECAST MODEL SOLUTIONS FOR THE SURFACE PATTERN FROM WEDNESDAY
AFTERNOON THROUGH THURSDAY HAVE BECOME MORE DIVERGENT OVER THE PAST
FEW RUNS...WITH QUITE A SPREAD IN THE LOCATION TRACK AND DEPTH OF A
SECOND SURFACE LOW WHICH IS EXPECTED TO DEVELOP SOMEWHERE ACROSS THE
OHIO OR TENNESSEE RIVER VALLEYS. OVERALL...GUIDANCE INDICATING A
WEAKER LOW DURING THIS PERIOD...THOUGH MODELS ARE OBVIOUSLY
STRUGGLING WITH DEVELOPMENT OF DIGGING SOUTHERN STREAM JET STREAK
AND THE RESULTING UPPER TROUGH AND DOWNSTREAM SURFACE LOW
DEVELOPMENT. WITH SUCH DIVERGENT SOLUTIONS HAVE AVOIDED MAKING LARGE
SWINGS IN THE FORECAST...AND HAVE HELD ON TO THE GENERAL SCENARIO OF
PREVIOUS FORECAST...THOUGH WITH SLIGHTLY WEAKER WIND FIELD DURING
THE LATE WEDNESDAY-THURSDAY PERIOD. ADJUSTMENTS WILL UNDOUBTEDLY BE
REQUIRED AS SUITE OF MODELS DEVELOP BETTER CONVERGENCE/AGREEMENT IN
THEIR SOLUTIONS.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210552
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1152 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210552
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1152 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS DEVELOPING PRE-DAWN AND LIKELY LINGERING THROUGH
  THE PERIOD.

* POTENTIAL FOR A PERIOD OF FOG/LIGHT FREEZING DRIZZLE THIS
  MORNING...THOUGH BETTER POTENTIAL WEST/NORTHWEST OF CHICAGO
  TERMINALS.

RATZER

//DISCUSSION...UPDATED 06Z...

LIGHT SOUTHWEST FLOW JUST ABOVE THE SURFACE IS ADVECTING LOW LEVEL
MOISTURE STEADILY NORTHEASTWARD ACROSS THE REGION...WITH EXPANSIVE
AREA OF MVFR/IFR/LIFR EXTENDING UPSTREAM TO THE WEST AND SOUTHWEST
OF NORTHERN ILLINOIS TERMINALS. MAIN MOIST AXIS AND LOWEST
CONDITIONS ALONG WITH FOG AND DRIZZLE/FREEZING DRIZZLE/FLURRIES
LIFTING FROM IOWA INTO NORTHWEST ILLINOIS...SETTING UP LIKELY IFR
CONDITIONS EARLY THIS MORNING FOR KRFD. FARTHER EAST...CHICAGO
AREA TERMINALS EXPECTED TO DETERIORATE TO MVFR BUT LOWER
CONDITIONS SHOULD REMAIN JUST OFF TO THE WEST/NORTHWEST. GIVEN
EXTENSIVE UPSTREAM CONDITIONS WOULD EXPECT LOW CLOUDS TO LINGER
THROUGH MUCH OF THE PERIOD AS SURFACE LOW PRESSURE DEVELOPING OVER
THE NORTHERN PLAINS MAINTAINS SOUTHWEST FLOW ALOFT.

SOUTH WINDS AROUND 5 KT WILL LIKELY BECOME A LITTLE EAST OF SOUTH
IN 170-160 DEGREE RANGE THROUGH THE DAY WITH SPEEDS INCREASING
INTO THE 10-15 KT RANGE. MODEL SOUNDINGS SUGGEST SOME GUSTS ABOVE
15 KT POSSIBLE LATER THIS AFTERNOON/TONIGHT...THOUGH SHALLOW MIXED
LAYER ARGUES AGAINST PREVAILING GUST MENTION.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM CONFIDENCE IN CEILING TRENDS THIS MORNING.

* LOW CONFIDENCE IN CEILING TRENDS THIS AFTERNOON/TONIGHT.

* LOW CONFIDENCE IN MVFR FOG AND DZ/FZDZ POTENTIAL THIS MORNING.

* MEDIUM-HIGH CONFIDENCE IN WINDS.

RATZER

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210537
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1137 PM CST Sat Dec 20 2014

.UPDATE...
ISSUED AT 857 PM CST SAT DEC 20 2014

Clouds cover most of the CWA tonight, but a small area in the east
and southeast is clear at the moment. Expect this area to cloud
over overnight. However, need to make some adjustments to the
cloud cover grids tonight. Remainder of grids look ok. Will send
an update on the forecast, but will not be a change for most of
the area. Changes will be in the east and southeast only.

&&

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CST SAT DEC 20 2014

Cloudy skies persist across much of central Illinois this afternoon:
however, 20z/2pm visible satellite imagery shows a large tear in the
overcast developing from near Decatur southeastward to Flora.
Although the HRRR has been a bit overdone with the clearing, it
continues to suggest at least thinning clouds across the E/SE KILX
CWA late this afternoon into the evening.  In fact, with 925mb winds
remaining light/variable and not really picking up a strong S/SW
component until Sunday, portions of the SE may see partly cloudy
conditions persist through the night.  Further north and west, low
clouds will be on the increase from the west.  Forecast soundings
and model RH profiles indicate that the lowest clouds/fog will
remain just W/NW of central Illinois tonight.  Due to cloud cover
and a light S/SE wind, low temperatures will be a couple of degrees
warmer than last night.  Coolest readings in the middle 20s will
occur south of I-70 where skies will likely remain partly cloudy,
while lows stay in the upper 20s/lower 30s elsewhere.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 259 PM CST SAT DEC 20 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1137 PM CST SAT DEC 20 2014

Cloudy skies will continue at all sites next 24hrs. Cigs are
hovering around 3kft with PIA and SPI above 3kft and BMI, DEC, and
CMI below. So will just have 3kft cigs at all sites since PIA and
SPI will likely drop below 3kft sometime overnight. Based on model
soundings and RH fields, am thinking the MVFR cigs will continue
through tomorrow and tomorrow night. Winds will be south-southeast
through the period, with speeds increase to around 10kts tomorrow
afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Auten
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Auten






000
FXUS63 KLOT 210321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CIGS LOWER TO MVFR LATE TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CIGS LOWER TO MVFR LATE TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CIGS LOWER TO MVFR LATE TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CIGS LOWER TO MVFR LATE TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CIGS LOWER TO MVFR LATE TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210321
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
921 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* CIGS LOWER TO MVFR LATE TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210316
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
916 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR LATER TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

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

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210316
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
916 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR LATER TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

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

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210316
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
916 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR LATER TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

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

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210316
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
916 PM CST SAT DEC 20 2014

.UPDATE...
904 PM CST

WE STILL HAVE THE POSSIBILITY OF PATCHY FREEZING DRIZZLE
OVERNIGHT WITH THE BEST CHANCE IN OUR WESTERN AREAS.  THAT
SAID...TEMPERATURES ARE AROUND FREEZING AND NOT EXPECTED TO DROP
MUCH GIVEN THE CLOUD COVER AND WARM ADVECTION PATTERN SETTING UP.
AT THIS POINT IMPACTS DO LOOK MINIMAL...ESPECIALLY FARTHER EAST.  HAVE
KEPT TEMPS NEARLY STEADY OVERNIGHT. SOME PRECIPITATION MAY MAKE IT
CLOSER TO CHICAGO LATE TONIGHT INTO SUNDAY MORNING ONCE THE WARM
FRONT GETS CLOSER...BUT IT WOULD BE LARGELY IN THE FORM OF PATCHY
DRIZZLE. FOG MAY BE POSSIBLE AS WELL OVERNIGHT.

KMD

&&

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR LATER TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI

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

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 210257
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
857 PM CST Sat Dec 20 2014

.UPDATE...
ISSUED AT 857 PM CST SAT DEC 20 2014

Clouds cover most of the CWA tonight, but a small area in the east
and southeast is clear at the moment. Expect this area to cloud
over overnight. However, need to make some adjustments to the
cloud cover grids tonight. Remainder of grids look ok. Will send
an update on the forecast, but will not be a change for most of
the area. Changes will be in the east and southeast only.

&&

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CST SAT DEC 20 2014

Cloudy skies persist across much of central Illinois this afternoon:
however, 20z/2pm visible satellite imagery shows a large tear in the
overcast developing from near Decatur southeastward to Flora.
Although the HRRR has been a bit overdone with the clearing, it
continues to suggest at least thinning clouds across the E/SE KILX
CWA late this afternoon into the evening.  In fact, with 925mb winds
remaining light/variable and not really picking up a strong S/SW
component until Sunday, portions of the SE may see partly cloudy
conditions persist through the night.  Further north and west, low
clouds will be on the increase from the west.  Forecast soundings
and model RH profiles indicate that the lowest clouds/fog will
remain just W/NW of central Illinois tonight.  Due to cloud cover
and a light S/SE wind, low temperatures will be a couple of degrees
warmer than last night.  Coolest readings in the middle 20s will
occur south of I-70 where skies will likely remain partly cloudy,
while lows stay in the upper 20s/lower 30s elsewhere.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 259 PM CST SAT DEC 20 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 534 PM CST SAT DEC 20 2014

Clouds will continue across all TAF sites next 24hrs. Believe MVFR
cigs will dominate the sites next 24hrs. However, VFR cigs are
occurring at PIA, SPI and CMI to start; but expecting them to drop
into MVFR category shortly. So, will have all starting at MVFR and
have a 3hr TEMPO group at all sites for VFR cigs. Remainder of the
night will see cigs drop to below 2kft but then improve to above
2kft tomorrow afternoon. All still remaining in the MVFR category.
Winds will be light south-southeast overnight and then become
southerly around 10kts tomorrow afternoon.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Auten
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Auten






000
FXUS63 KILX 210257
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
857 PM CST Sat Dec 20 2014

.UPDATE...
ISSUED AT 857 PM CST SAT DEC 20 2014

Clouds cover most of the CWA tonight, but a small area in the east
and southeast is clear at the moment. Expect this area to cloud
over overnight. However, need to make some adjustments to the
cloud cover grids tonight. Remainder of grids look ok. Will send
an update on the forecast, but will not be a change for most of
the area. Changes will be in the east and southeast only.

&&

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CST SAT DEC 20 2014

Cloudy skies persist across much of central Illinois this afternoon:
however, 20z/2pm visible satellite imagery shows a large tear in the
overcast developing from near Decatur southeastward to Flora.
Although the HRRR has been a bit overdone with the clearing, it
continues to suggest at least thinning clouds across the E/SE KILX
CWA late this afternoon into the evening.  In fact, with 925mb winds
remaining light/variable and not really picking up a strong S/SW
component until Sunday, portions of the SE may see partly cloudy
conditions persist through the night.  Further north and west, low
clouds will be on the increase from the west.  Forecast soundings
and model RH profiles indicate that the lowest clouds/fog will
remain just W/NW of central Illinois tonight.  Due to cloud cover
and a light S/SE wind, low temperatures will be a couple of degrees
warmer than last night.  Coolest readings in the middle 20s will
occur south of I-70 where skies will likely remain partly cloudy,
while lows stay in the upper 20s/lower 30s elsewhere.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 259 PM CST SAT DEC 20 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 534 PM CST SAT DEC 20 2014

Clouds will continue across all TAF sites next 24hrs. Believe MVFR
cigs will dominate the sites next 24hrs. However, VFR cigs are
occurring at PIA, SPI and CMI to start; but expecting them to drop
into MVFR category shortly. So, will have all starting at MVFR and
have a 3hr TEMPO group at all sites for VFR cigs. Remainder of the
night will see cigs drop to below 2kft but then improve to above
2kft tomorrow afternoon. All still remaining in the MVFR category.
Winds will be light south-southeast overnight and then become
southerly around 10kts tomorrow afternoon.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Auten
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Auten







000
FXUS63 KLOT 202359
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
559 PM CST SAT DEC 20 2014

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR LATER TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI


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

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 202359
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
559 PM CST SAT DEC 20 2014

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* CIGS LOWER TO MVFR LATER TONIGHT AND POTENTIALLY TO IFR SUNDAY
* SLIGHT CHANCE OF -FZDZ OR -DZ SUNDAY MORNING

IZZI

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

HAVE LARGELY FOLLOWED THE TRENDS FROM PREVIOUS SET OF TAFS WITH
LOWERING CIGS TONIGHT/SUNDAY...THOUGH HAVE SPED UP THE ARRIVAL OF
MVFR CIGS TONIGHT AND LOWERED CIGS A BIT SUNDAY. EXPANSIVE AREA OF
IFR/BR/-DZ BLANKETS IOWA AND SHOULD SLOWLY SPREAD EASTWARD THROUGH
THE PERIOD. ONLY BRINGING CIGS DOWN TO LOWER END MVFR SUNDAY COULD
END UP BEING TOO OPTIMISTIC FOR ORD/MDW/GYY...WILL MONITOR TRENDS
IN THE EASTWARD EXPANSION OF IFR/LIFR TONIGHT AND WE MAY NEED TO
ADD IFR INTO THE TAFS FOR CHICAGO TERMINALS IN LATER FORECASTS. AS
WELL...IF CIGS DO DROP LOWER THEN POTENTIAL WOULD BE GREATER FOR
SOME -FZDZ TRANSITIONING TO -DZ AS TEMPS INCH UPWARD. NOT
ANTICIPATING CIGS TO LIFT MUCH FROM MORNING LOWS SUNDAY...SO IFE
CONDITIONS DEVELOP THEY COULD PERSIST THROUGH THE DAY. CERTAINLY
COULD SEE SOME OCNL GUSTS OF 15-20KT SUNDAY AFTERNOON FROM THE
SSE...BUT THINKING THE EXPECTED STRATUS DECK SHOULD LIMIT MIXING
ENOUGH TO KEEP GUSTINESS SPORADIC TO OCNL AT BEST.

IZZI


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

* MEDIUM CONFIDENCE IN CIG TRENDS THROUGH SUNDAY MORNING...LOW
  CONFIDENCE IN TIMING AND HOW LOW CIGS GET
* LOW CONFIDENCE IN CIGS SUNDAY AFTERNOON
* LOW CONFIDENCE IN DZ/FZDZ POTENTIAL SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WINDS

IZZI

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

MONDAY...MVFR/IFR EARLY LOWERING TO IFR/LIFR. RAIN DEVELOPING
LATE.

TUESDAY...ONCL SHRA. IFR PROBABLE.

WEDNESDAY...CHANCE SHRA/SHSN. MVFR LIKELY. IFR POSSIBLE.

THURSDAY...MVFR CIGS POSSIBLE EARLY.

FRIDAY...CHANCE OF RA/SN LATE. MVFR CIGS POSSIBLE AGAIN.

IZZI

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 202334
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
534 PM CST Sat Dec 20 2014

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CST SAT DEC 20 2014

Cloudy skies persist across much of central Illinois this afternoon:
however, 20z/2pm visible satellite imagery shows a large tear in the
overcast developing from near Decatur southeastward to Flora.
Although the HRRR has been a bit overdone with the clearing, it
continues to suggest at least thinning clouds across the E/SE KILX
CWA late this afternoon into the evening.  In fact, with 925mb winds
remaining light/variable and not really picking up a strong S/SW
component until Sunday, portions of the SE may see partly cloudy
conditions persist through the night.  Further north and west, low
clouds will be on the increase from the west.  Forecast soundings
and model RH profiles indicate that the lowest clouds/fog will
remain just W/NW of central Illinois tonight.  Due to cloud cover
and a light S/SE wind, low temperatures will be a couple of degrees
warmer than last night.  Coolest readings in the middle 20s will
occur south of I-70 where skies will likely remain partly cloudy,
while lows stay in the upper 20s/lower 30s elsewhere.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 259 PM CST SAT DEC 20 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 534 PM CST SAT DEC 20 2014

Clouds will continue across all TAF sites next 24hrs. Believe MVFR
cigs will dominate the sites next 24hrs. However, VFR cigs are
occurring at PIA, SPI and CMI to start; but expecting them to drop
into MVFR category shortly. So, will have all starting at MVFR and
have a 3hr TEMPO group at all sites for VFR cigs. Remainder of the
night will see cigs drop to below 2kft but then improve to above
2kft tomorrow afternoon. All still remaining in the MVFR category.
Winds will be light south-southeast overnight and then become
southerly around 10kts tomorrow afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Auten






000
FXUS63 KILX 202334
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
534 PM CST Sat Dec 20 2014

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CST SAT DEC 20 2014

Cloudy skies persist across much of central Illinois this afternoon:
however, 20z/2pm visible satellite imagery shows a large tear in the
overcast developing from near Decatur southeastward to Flora.
Although the HRRR has been a bit overdone with the clearing, it
continues to suggest at least thinning clouds across the E/SE KILX
CWA late this afternoon into the evening.  In fact, with 925mb winds
remaining light/variable and not really picking up a strong S/SW
component until Sunday, portions of the SE may see partly cloudy
conditions persist through the night.  Further north and west, low
clouds will be on the increase from the west.  Forecast soundings
and model RH profiles indicate that the lowest clouds/fog will
remain just W/NW of central Illinois tonight.  Due to cloud cover
and a light S/SE wind, low temperatures will be a couple of degrees
warmer than last night.  Coolest readings in the middle 20s will
occur south of I-70 where skies will likely remain partly cloudy,
while lows stay in the upper 20s/lower 30s elsewhere.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 259 PM CST SAT DEC 20 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 534 PM CST SAT DEC 20 2014

Clouds will continue across all TAF sites next 24hrs. Believe MVFR
cigs will dominate the sites next 24hrs. However, VFR cigs are
occurring at PIA, SPI and CMI to start; but expecting them to drop
into MVFR category shortly. So, will have all starting at MVFR and
have a 3hr TEMPO group at all sites for VFR cigs. Remainder of the
night will see cigs drop to below 2kft but then improve to above
2kft tomorrow afternoon. All still remaining in the MVFR category.
Winds will be light south-southeast overnight and then become
southerly around 10kts tomorrow afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Auten







000
FXUS63 KLOT 202201
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
401 PM CST SAT DEC 20 2014

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD/IZZI

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD/IZZI

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 202201
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
401 PM CST SAT DEC 20 2014

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD/IZZI

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD/IZZI

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 202100
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
300 PM CST Sat Dec 20 2014

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CST SAT DEC 20 2014

Cloudy skies persist across much of central Illinois this afternoon:
however, 20z/2pm visible satellite imagery shows a large tear in the
overcast developing from near Decatur southeastward to Flora.
Although the HRRR has been a bit overdone with the clearing, it
continues to suggest at least thinning clouds across the E/SE KILX
CWA late this afternoon into the evening.  In fact, with 925mb winds
remaining light/variable and not really picking up a strong S/SW
component until Sunday, portions of the SE may see partly cloudy
conditions persist through the night.  Further north and west, low
clouds will be on the increase from the west.  Forecast soundings
and model RH profiles indicate that the lowest clouds/fog will
remain just W/NW of central Illinois tonight.  Due to cloud cover
and a light S/SE wind, low temperatures will be a couple of degrees
warmer than last night.  Coolest readings in the middle 20s will
occur south of I-70 where skies will likely remain partly cloudy,
while lows stay in the upper 20s/lower 30s elsewhere.


&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 259 PM CST SAT DEC 20 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1140 AM CST SAT DEC 20 2014

MVFR ceilings will gradually spread across central Illinois this
afternoon/evening. 17z/11am obs show MVFR conditions
along/southwest of a KGBG to KSPI line, with VFR ceilings further
east across the remainder of the area. As light S/SE flow
gradually becomes more S/SW, these lower clouds will return to all
terminals by evening. Based on the latest HRRR output, have
introduced MVFR at KPIA by 21z, then further east to KCMI by 03z.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Barnes






000
FXUS63 KILX 202100
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
300 PM CST Sat Dec 20 2014

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CST SAT DEC 20 2014

Cloudy skies persist across much of central Illinois this afternoon:
however, 20z/2pm visible satellite imagery shows a large tear in the
overcast developing from near Decatur southeastward to Flora.
Although the HRRR has been a bit overdone with the clearing, it
continues to suggest at least thinning clouds across the E/SE KILX
CWA late this afternoon into the evening.  In fact, with 925mb winds
remaining light/variable and not really picking up a strong S/SW
component until Sunday, portions of the SE may see partly cloudy
conditions persist through the night.  Further north and west, low
clouds will be on the increase from the west.  Forecast soundings
and model RH profiles indicate that the lowest clouds/fog will
remain just W/NW of central Illinois tonight.  Due to cloud cover
and a light S/SE wind, low temperatures will be a couple of degrees
warmer than last night.  Coolest readings in the middle 20s will
occur south of I-70 where skies will likely remain partly cloudy,
while lows stay in the upper 20s/lower 30s elsewhere.


&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 259 PM CST SAT DEC 20 2014

Still looking like only one major system to impact central and
southeast Illinois through the coming week. Unfortunately, the
potential exists for the biggest travel headaches with this system
to arrive later Tuesday night into Christmas Eve. However, it should
be noted that no model consensus exists with respect to this
system`s snow potential locally. In fact, at this point, more model
solutions keep the snowfall minimal than not. Nevertheless, it would
be prudent to keep an eye on the forecast heading into the Christmas
holiday as the ultimate outcome becomes more clear.

High pressure at the surface and mostly neutral upper flow aloft
will keep its grip on the local weather for one more day on Sunday.
Southerly return flow on the back side of the surface ridge will
push temperatures a few degrees warmer than today. Meanwhile, a
vigorous upper wave, currently crashing ashore along the Pacific
Northwest coast, will begin to dig a significant trof over the
Plains, also inducing surface cyclogenesis.

Strong WAA/isentropic ascent ahead of this slow moving system will
begin to spread rain into the area on Monday. The rain chances will
continue into Monday night and Tuesday. This initial part of the
forecast is fairly well agreed upon by the models.

The initial surface low beneath the mean Plains upper trof will not
move much across the northern Plains into the upper Midwest between
Monday and Tuesday. Attention then turns to another vigorous wave
that will round the base of the mean trof Tuesday into Wednesday.
This wave should induce a second surface low, one that will become
dominant, as it lifts northeast into Canada by the end of the week.
The model agreement with the timing/track/strength of this secondary
low by Tuesday night into Wednesday is not very good. The track of
this low is critical to how quickly our precipitation will change
over to snow Tuesday night into Wednesday, and if we will be
impacted by the heavier snowfall within this system`s deformation
zone. While the threat is certainly there, at this point only the
GFS has been impacting the forecast area very significantly.

Behind the midweek system, another wave will arrive by Friday.
However, the models have been trending weaker with this system
overall, as well as drier. So, have backed away from rain and/or
snow chances as this system arrives.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1140 AM CST SAT DEC 20 2014

MVFR ceilings will gradually spread across central Illinois this
afternoon/evening. 17z/11am obs show MVFR conditions
along/southwest of a KGBG to KSPI line, with VFR ceilings further
east across the remainder of the area. As light S/SE flow
gradually becomes more S/SW, these lower clouds will return to all
terminals by evening. Based on the latest HRRR output, have
introduced MVFR at KPIA by 21z, then further east to KCMI by 03z.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Barnes







000
FXUS63 KLOT 202050
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CST SAT DEC 20 2014

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 202050
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CST SAT DEC 20 2014

.SHORT TERM...
247 PM CST

THROUGH SUNDAY NIGHT...

THE STREAK OF CLOUDY DAYS CONTINUES...WITH THE STUBBORN PATTERN TO
CONTINUE. AS A RESULT OF THE THICK CLOUD COVER...AND LACK OF
ORGANIZED ADVECTION OF ANY WARMER AIR AT THE SFC...TEMPS HAVE HELD
MAINLY ARND 30 TO 35 ACROSS THE BULK OF THE CWFA. SFC RIDGE
CONTINUES TO DRIFT EAST THIS AFTN...WITH A WEAK SOUTHERLY FLOW
DEVELOPING. THERE WAS A WEAK MID-LVL VORT LIFTING NORTHEAST ACROSS
SOUTHERN WISC/WESTERN LOWER MI...WHICH WAS ABLE TO PRODUCE A FEW
FLURRIES ACROSS THE FAR NORTHERN IL AREAS.

THIS AFTN/EARLY EVE LOOKS TO REMAIN QUIET/DRY...WITH A LIGHT
SOUTH/SOUTHEAST WIND. IR IMAGERY SHOWS THE NEXT WAVE ACROSS THE
CENTRAL PLAINS...WHICH IS PROGGED TO ARRIVE ACROSS NORTHWEST IL
AFTER MIDNIGHT. THERE APPEARS TO BE SOME WEAK ADVECTION OF MOISTURE
IN THE LOW-LEVELS OVERNIGHT. SOUNDINGS SUGGEST A NARROW WARM WEDGE
ALOFT WHICH COULD TRANSITION ANY PRECIP OVERNIGHT TO LIQUID. THE
FORCING/OMEGA IS RATHER WEAK...WHICH MAY LIMIT DROPLET SIZE AND
RESULT IN JUST PATCHY FREEZING DRIZZLE. TEMPS WILL LIKELY NOT MOVE
MUCH OVERNIGHT...SO HAVE HELD ONTO MID/UPR 20S OVERNIGHT.

LOCAL ARW8KM SOLUTION INDICATES THE MOISTURE TO BE RATHER MARGINAL
WITH THE SYSTEM ARRIVING OVERNIGHT/SUN MORNING...BUT PROGRESSIVE AND
LIFTING NORTH OF THE CWFA BY MIDDAY. WEAK THERMAL RIDGE AT 850MB
WOULD SUGGEST TEMPS MAY ACTUALLY WARM SUN AFTN...HOWEVER GIVEN THE
STUBBORN PATTERN WE HAVE BEEN IN WOULD LEAN TOWARDS NUDGING TEMPS
DOWN A DEGREE OR TWO. MOISTURE LAYER WILL REMAIN LOCKED IN ACROSS
THE REGION THRU SUN/SUN NGT. WITH A CONTINUED SOUTHERLY FLOW AT THE
SFC...TEMPS WILL LIKELY ONLY FALL TO ARND 30/LOW 30S.

BEACHLER

&&

.LONG TERM...
247 PM CST

MONDAY THROUGH SATURDAY...

500MB TROUGH BEGINS TO DIG INTO THE CENTRAL CONUS MON MORNING...WITH
WARM AIR STEADILY ADVECTING NORTH ACROSS THE FORECAST AREA. WHILE
THE THICK CLOUD COVER WILL PERSIST...THE PUSH OF WARM/MOIST AIR WILL
BRING TEMPS INTO THE 40S THE FAR SOUTHERN CWFA COULD SEE A FEW
LOCATIONS TOUCH THE UPR 40S MON AFTN. PRECIP WILL STEADILY PUSH EAST
AS THE UPPER LEVEL SYSTEM PROGRESSES TOWARDS THE REGION...BUT WITH
THE WARM AIR IN PLACE PRECIP SHUD FALL AS RAIN.

MON NGT THE 500MB VORT WILL SLIDE INTO THE UPPER MIDWEST...BUT THE
TROUGH WILL DIG SOUTH ACROSS THE SOUTHERN PLAINS. GUIDANCE HAS BEEN
INDICATING A SECONDARY SHORTWAVE EJECTING FROM THE TROUGH AXIS...AND
LIFTING IT NORTHEAST ACROSS THE TENN VALLEY CHRISTMAS EVE. THE
NORTHERN SFC LOW WILL BE WRAPPED UP ACROSS CENTRAL WISC TUE...WITH
THE MOIST CHANNEL FEEDING NORTH ACROSS THE FORECAST AREA THRU TUE
AFTN. THE SOUTHERN LOW WILL BE QUICKLY DEEPENING AS IT LIFTS NORTH
ACROSS THE OHIO VALLEY WED MORNING...ALLOWING WINDS TO BE ON THE
INCREASE AND HELPING TO STEADILY TRANSITION PRECIP OVER FROM RAIN TO
SNOW POST FROPA WED MORNING.

THE LAST SEVERAL CYCLES OF GUIDANCE HAVE DEMONSTRATED DIFFERENCES IN
PLACEMENT/TRACK OF THE SFC LOW WED AFTN/EVE. LATEST SOLUTION IS
PROGGED TO LIFT NORTH ACROSS NORTHERN IN AND THEN SLIGHTLY
RETROGRADE ACROSS THE SOUTHERN TIP OF LAKE MICHIGAN WED EVE. THEN BY
CHRISTMAS DAY THE TROUGH WILL BE PIVOTING EAST AND HELPING TO LIFT
THE SFC LOW NORTHEAST AWAY FROM THE REGION. SOME WRAP AROUND
MOISTURE/SNOW LOOKS FAVORABLE WED NGT/THUR MORNING...BEFORE COMING
TO AN END JUST AFTER DAYBREAK CHRISTMAS MORNING. THIS SYSTEM WILL
CONTINUE TO BE CLOSELY MONITORED.

TEMPS WILL BE RETURNING TO MORE SEASONAL CONDS...WITH HIGHS
CHRISTMAS DAY IN THE LOW/MID 30S. FLOW REMAINS RATHER PROGRESSIVE
WITH ANOTHER WEAK PUSH OF WARMER AIR RETURNING FRI AND TEMPS BACK TO
THE UPR 30S/LOW 40S. THEN FOR FRI ENSEMBLES ARE INDICATING YET
ANOTHER TROUGH BEGINNING TO DIG INTO THE CENTRAL CONUS...WITH A SFC
LOW LIFTING NORTHEAST ACROSS THE WESTERN GREAT LAKES.

BEACHLER

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740...10 PM SUNDAY TO 3 AM TUESDAY.

&&

$$

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 202004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 202004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 202004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 202004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
203 PM CST

LIGHT SOUTHEAST TO EAST WINDS WILL INCREASE TO 10-25 KT TOMORROW
MORNING THEN TO 30 KT IN THE AFTERNOON AS THE GRADIENT TIGHTENS
BETWEEN THE DEPARTING HIGH AND THE NEXT LOW. THE LOW MOVES OVER THE
DAKOTAS SUNDAY NIGHT AND MODELS AGREE A BIT MORE IN THE PATTERN
EARLY NEXT WEEK.  HAVE MEDIUM CONFIDENCE IN THE WIND FORECAST WITH
THIS NEXT LOW.  THE LOW WEAKENS AS IT MOVES OVER WISCONSIN TUESDAY
AND A SECOND LOW FORMS OVER THE SOUTHERN MISSISSIPPI VALLEY TUESDAY
AFTERNOON. THE SECOND LOW WILL RACE NORTH AND DEEPEN REACHING
MICHIGAN WEDNESDAY. MODELS DIFFER ON HOW QUICKLY THE LOW WILL REACH
MICHIGAN.  BOTH MODELS CONTINUE TO FEATURE WESTERLY HIGH END GALES
BEHIND THE LOW WEDNESDAY AFTERNOON INTO THURSDAY.  WEST WINDS
DIMINISH THURSDAY AS THE LOW CONTINUES OFF TO THE NORTH. THE NEXT
LOW MOVES OVER THE SOUTHERN PLAINS THURSDAY AFTERNOON. GUIDANCE
DIFFERS ON THIS LOWS PATH BUT IT SHOULD IMPACT THE LAKE LATE NEXT
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201753
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1153 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201753
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1153 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CIGS RETURNING THIS EVENING OR OVERNIGHT.
* PATCHY FREEZING DRIZZLE EARLY SUNDAY.

BMD

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

HIGH PRESSURE REMAINS OVER THE REGION TODAY RESULTING IN LIGHT
FLOW...HOWEVER WINDS WILL TREND MORE SOUTHERLY THOUGH THE TAF PERIOD
AS THE HIGH DRIFTS EAST OF THE AREA. MVFR CIGS HAVE SCATTERED AND
DRIFTED EAST OF THE TERMINALS THIS MORNING...BUT EXPECT A RETURN OF
THE MVFR THIS EVENING OR OVERNIGHT...THOUGH SPECIFIC TIMING REMAINS
UNCERTAIN. OVERNIGHT...WARM AIR ADVECTION INCREASES JUST OFF THE
DECK AND MAY ALLOW FOR SOME LIGHT FREEZING DRIZZLE TO DEVELOP WITH
SURFACE TEMPS JUST BELOW FREEZING. FORCING IS BEST OVER NORTH
CENTRAL ILLINOIS SO WILL MAINTAIN PROB30 MENTION AT RFD ONLY FOR
NOW. WINDS WILL GRADUALLY INCREASE THROUGH THE DAY SUNDAY AS THE
GRADIENT TIGHTENS AHEAD OF LOW PRESSURE APPROACHING FROM THE
NORTHWEST.

BMD

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

* MEDIUM CONFIDENCE IN CIG TRENDS BUT LOW IN TIMING.
* LOW CONFIDENCE IN FREEZING DRIZZLE.

BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KILX 201740
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1140 AM CST Sat Dec 20 2014

.UPDATE...
ISSUED AT 1045 AM CST SAT DEC 20 2014

Short-wave trough evident on latest water vapor imagery across
north-central Illinois will continue to track eastward out of the
area this afternoon. Despite weak synoptic lift associated with
this feature, little or no light precip has been observed. Clouds
blanket central Illinois, with lower clouds/fog remaining further
west across Iowa into northern/central Missouri. 16z LAPS soundings
show a dry layer below 900mb, which is not conducive for drizzle.
As a result, have removed the drizzle/flurry mention across the
far northern KILX CWA this morning. Will generally be a cloudy and
cold day across central Illinois: however, a few breaks in the
overcast will be possible from time to time. As low-level flow
gradually veers more southwesterly, lower clouds/drizzle/fog
currently west of the Mississippi River will spill eastward into
the Illinois River Valley tonight.

&&

.SHORT TERM...(Today)
ISSUED AT 507 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 507 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be in between strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1140 AM CST SAT DEC 20 2014

MVFR ceilings will gradually spread across central Illinois this
afternoon/evening. 17z/11am obs show MVFR conditions
along/southwest of a KGBG to KSPI line, with VFR ceilings further
east across the remainder of the area. As light S/SE flow
gradually becomes more S/SW, these lower clouds will return to all
terminals by evening. Based on the latest HRRR output, have
introduced MVFR at KPIA by 21z, then further east to KCMI by 03z.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Barnes







000
FXUS63 KILX 201740
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1140 AM CST Sat Dec 20 2014

.UPDATE...
ISSUED AT 1045 AM CST SAT DEC 20 2014

Short-wave trough evident on latest water vapor imagery across
north-central Illinois will continue to track eastward out of the
area this afternoon. Despite weak synoptic lift associated with
this feature, little or no light precip has been observed. Clouds
blanket central Illinois, with lower clouds/fog remaining further
west across Iowa into northern/central Missouri. 16z LAPS soundings
show a dry layer below 900mb, which is not conducive for drizzle.
As a result, have removed the drizzle/flurry mention across the
far northern KILX CWA this morning. Will generally be a cloudy and
cold day across central Illinois: however, a few breaks in the
overcast will be possible from time to time. As low-level flow
gradually veers more southwesterly, lower clouds/drizzle/fog
currently west of the Mississippi River will spill eastward into
the Illinois River Valley tonight.

&&

.SHORT TERM...(Today)
ISSUED AT 507 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 507 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be in between strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1140 AM CST SAT DEC 20 2014

MVFR ceilings will gradually spread across central Illinois this
afternoon/evening. 17z/11am obs show MVFR conditions
along/southwest of a KGBG to KSPI line, with VFR ceilings further
east across the remainder of the area. As light S/SE flow
gradually becomes more S/SW, these lower clouds will return to all
terminals by evening. Based on the latest HRRR output, have
introduced MVFR at KPIA by 21z, then further east to KCMI by 03z.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Barnes






000
FXUS63 KILX 201645
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1045 AM CST Sat Dec 20 2014

.UPDATE...
ISSUED AT 1045 AM CST SAT DEC 20 2014

Short-wave trough evident on latest water vapor imagery across
north-central Illinois will continue to track eastward out of the
area this afternoon. Despite weak synoptic lift associated with
this feature, little or no light precip has been observed. Clouds
blanket central Illinois, with lower clouds/fog remaining further
west across Iowa into northern/central Missouri. 16z LAPS soundings
show a dry layer below 900mb, which is not conducive for drizzle.
As a result, have removed the drizzle/flurry mention across the
far northern KILX CWA this morning. Will generally be a cloudy and
cold day across central Illinois: however, a few breaks in the
overcast will be possible from time to time. As low-level flow
gradually veers more southwesterly, lower clouds/drizzle/fog
currently west of the Mississippi River will spill eastward into
the Illinois River Valley tonight.

&&

.SHORT TERM...(Today)
ISSUED AT 507 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 507 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be inbetween strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 510 AM CST SAT DEC 20 2014

MVFR vsbys in fog/haze will occur thru 15z this morning and then a
gradual lowering of cigs to MVFR from west to east later this
morning into the afternoon hours. Weather system out to our west will
track across the area later this morning but as it heads east into
our area, moisture will be quite limited. As a result, other than
some scattered flurries, not major problems in precip are expected
with this system. We should see the cigs start to lower as the MVFR
and even some IFR cigs have been held out of our area all night thanks
to a persistent area of high pressure over east central IL. As the
high drifts off to our east this afternoon, we expect the lower clouds
that have been out to our west, to start to drift into parts of central
IL. Once the cigs lower to MVFR, expect at least MVFR conditions
tonight if not lower as a light southerly flow transports more moisture
in the lower levels into our area. Right now will hold with MVFR cigs
but could see some tempo IFR conditions, especially at PIA later this
evening. Surface winds will once again be a non-factor with a light
southeast to south flow expected today and tonight with speeds of less
than 10 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith







000
FXUS63 KILX 201645
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1045 AM CST Sat Dec 20 2014

.UPDATE...
ISSUED AT 1045 AM CST SAT DEC 20 2014

Short-wave trough evident on latest water vapor imagery across
north-central Illinois will continue to track eastward out of the
area this afternoon. Despite weak synoptic lift associated with
this feature, little or no light precip has been observed. Clouds
blanket central Illinois, with lower clouds/fog remaining further
west across Iowa into northern/central Missouri. 16z LAPS soundings
show a dry layer below 900mb, which is not conducive for drizzle.
As a result, have removed the drizzle/flurry mention across the
far northern KILX CWA this morning. Will generally be a cloudy and
cold day across central Illinois: however, a few breaks in the
overcast will be possible from time to time. As low-level flow
gradually veers more southwesterly, lower clouds/drizzle/fog
currently west of the Mississippi River will spill eastward into
the Illinois River Valley tonight.

&&

.SHORT TERM...(Today)
ISSUED AT 507 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 507 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be inbetween strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 510 AM CST SAT DEC 20 2014

MVFR vsbys in fog/haze will occur thru 15z this morning and then a
gradual lowering of cigs to MVFR from west to east later this
morning into the afternoon hours. Weather system out to our west will
track across the area later this morning but as it heads east into
our area, moisture will be quite limited. As a result, other than
some scattered flurries, not major problems in precip are expected
with this system. We should see the cigs start to lower as the MVFR
and even some IFR cigs have been held out of our area all night thanks
to a persistent area of high pressure over east central IL. As the
high drifts off to our east this afternoon, we expect the lower clouds
that have been out to our west, to start to drift into parts of central
IL. Once the cigs lower to MVFR, expect at least MVFR conditions
tonight if not lower as a light southerly flow transports more moisture
in the lower levels into our area. Right now will hold with MVFR cigs
but could see some tempo IFR conditions, especially at PIA later this
evening. Surface winds will once again be a non-factor with a light
southeast to south flow expected today and tonight with speeds of less
than 10 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith






000
FXUS63 KLOT 201604
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1004 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* PERIODS OF VFR AT TERMINALS TODAY...THEN LIKELY MVFR TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER/BMD

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER

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

* LOW-MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER/BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201604
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1004 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* PERIODS OF VFR AT TERMINALS TODAY...THEN LIKELY MVFR TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER/BMD

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER

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

* LOW-MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER/BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201406
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
806 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS WITH PATCHES OF VFR NEAR TERMINALS TODAY...THEN
  LIKELY MVFR TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER/BMD

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER

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

* LOW-MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER/BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201406
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
806 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS WITH PATCHES OF VFR NEAR TERMINALS TODAY...THEN
  LIKELY MVFR TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER/BMD

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER

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

* LOW-MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER/BMD

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201246
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
646 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS SCATTERING/RAISING TO VFR THIS MORNING... THEN
  LIKELY LOWERING TO MVFR AGAIN TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER

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

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201246
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
646 AM CST SAT DEC 20 2014

.SHORT TERM...
302 AM CST

TODAY THROUGH SUNDAY...

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
347 AM CST

MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS SCATTERING/RAISING TO VFR THIS MORNING... THEN
  LIKELY LOWERING TO MVFR AGAIN TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER

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

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201153
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
553 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
FXUS63 KLOT 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS SCATTERING/RAISING TO VFR THIS MORNING... THEN
  LIKELY LOWERING TO MVFR AGAIN TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER


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

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201153
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
553 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
FXUS63 KLOT 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS SCATTERING/RAISING TO VFR THIS MORNING... THEN
  LIKELY LOWERING TO MVFR AGAIN TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER


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

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201153
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
553 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
FXUS63 KLOT 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS SCATTERING/RAISING TO VFR THIS MORNING... THEN
  LIKELY LOWERING TO MVFR AGAIN TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER


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

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201153
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
553 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
FXUS63 KLOT 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.AVIATION...

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

* MVFR CEILINGS SCATTERING/RAISING TO VFR THIS MORNING... THEN
  LIKELY LOWERING TO MVFR AGAIN TONIGHT.

* POTENTIAL FOR SOME LIGHT FREEZING DRIZZLE SUNDAY MORNING.

RATZER

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

DIFFUSE SURFACE HIGH PRESSURE RIDGE DRIFTING EAST ACROSS TERMINALS
EARLY THIS MORNING. LIGHT WINDS AND SHALLOW INVERSION CONTINUE TO
PLAGUE THE REGION WITH EXTENSIVE MVFR CEILINGS...THOUGH SIZABLE
AREA OF VFR ACROSS WESTERN/CENTRAL IL HAS BEEN DEVELOPING SLOWLY
NORTHEAST WITH TIME OVERNIGHT...AND WILL LIKELY ALLOW FOR
SCATTERING OF MVFR CIGS AT AREA TERMINALS THIS MORNING. MODEL
FORECAST GUIDANCE INDICATES AREA WILL LIKELY REMAIN ALONG VFR/MVFR
INTERFACE TO THE EAST...SO HOUR TO HOUR DETAILS OF CEILING DETAILS
A LITTLE UNCERTAIN. CEILINGS EXPECTED TO GRADUALLY LOWER BACK INTO
MVFR RANGE TONIGHT...WITH THE POTENTIAL FOR SOME LIGHT
PRECIPITATION IN THE FORM OF FREEZING DRIZZLE TOWARD SUNDAY
MORNING ESPECIALLY ACROSS KRFD AREA.

SURFACE RIDGE AXIS APPEARS TO BE PASSING EAST OF ORD/MDW AT 12Z...
WITH LIGHT SOUTHWEST WINDS TO GRADUALLY BECOME SOUTHERLY LATE
TODAY AND TONIGHT.

RATZER


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

* MEDIUM CONFIDENCE IN CEILING TRENDS.

* LOW CONFIDENCE IN -FZDZ SUNDAY MORNING.

RATZER

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

SUNDAY NIGHT...DRY...MAINLY VFR.

MONDAY...RAIN AND MVFR LIKELY. BREEZY SOUTH-SOUTHEAST WINDS.

TUESDAY...CHANCE OF RAIN. MVFR POSSIBLE. SOUTH WINDS BECOMING WEST.

WEDNESDAY...CHANCE OF SNOW. MVFR/IFR POSSIBLE. NORTHWEST WINDS
BECOMING GUSTY FROM THE WEST.

THURSDAY...DRY. MAINLY VFR. GUSTY WEST WINDS DIMINISHING.

FRIDAY...CHANCE OF RAIN OR SNOW. MVFR POSSIBLE. LIGHT EAST WINDS
BECOMING WEST.

RATZER

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 201112
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
512 AM CST Sat Dec 20 2014

.SHORT TERM...(Today)
ISSUED AT 507 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.


&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 507 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be inbetween strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.


&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 510 AM CST SAT DEC 20 2014

MVFR vsbys in fog/haze will occur thru 15z this morning and then a
gradual lowering of cigs to MVFR from west to east later this
morning into the afternoon hours. Weather system out to our west will
track across the area later this morning but as it heads east into
our area, moisture will be quite limited. As a result, other than
some scattered flurries, not major problems in precip are expected
with this system. We should see the cigs start to lower as the MVFR
and even some IFR cigs have been held out of our area all night thanks
to a persistent area of high pressure over east central IL. As the
high drifts off to our east this afternoon, we expect the lower clouds
that have been out to our west, to start to drift into parts of central
IL. Once the cigs lower to MVFR, expect at least MVFR conditions
tonight if not lower as a light southerly flow transports more moisture
in the lower levels into our area. Right now will hold with MVFR cigs
but could see some tempo IFR conditions, especially at PIA later this
evening. Surface winds will once again be a non-factor with a light
southeast to south flow expected today and tonight with speeds of less
than 10 kts.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith





000
FXUS63 KILX 201112
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
512 AM CST Sat Dec 20 2014

.SHORT TERM...(Today)
ISSUED AT 507 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.


&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 507 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be inbetween strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.


&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
ISSUED AT 510 AM CST SAT DEC 20 2014

MVFR vsbys in fog/haze will occur thru 15z this morning and then a
gradual lowering of cigs to MVFR from west to east later this
morning into the afternoon hours. Weather system out to our west will
track across the area later this morning but as it heads east into
our area, moisture will be quite limited. As a result, other than
some scattered flurries, not major problems in precip are expected
with this system. We should see the cigs start to lower as the MVFR
and even some IFR cigs have been held out of our area all night thanks
to a persistent area of high pressure over east central IL. As the
high drifts off to our east this afternoon, we expect the lower clouds
that have been out to our west, to start to drift into parts of central
IL. Once the cigs lower to MVFR, expect at least MVFR conditions
tonight if not lower as a light southerly flow transports more moisture
in the lower levels into our area. Right now will hold with MVFR cigs
but could see some tempo IFR conditions, especially at PIA later this
evening. Surface winds will once again be a non-factor with a light
southeast to south flow expected today and tonight with speeds of less
than 10 kts.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...Smith




000
FXUS63 KLOT 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&


LONG TERM...MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&


LONG TERM...MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&


LONG TERM...MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SAT DEC 20 2014

.SHORT TERM...
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014

...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&


LONG TERM...MONDAY THROUGH FRIDAY...

NOT MUCH HAS CHANGED IN THE EXPECTATION OF A TRANSITIONING WEATHER
PATTERN ACROSS THE CONUS SUPPORTIVE OF SEVERAL PERIODS OF INCLEMENT
WEATHER THROUGH MUCH OF THE UPCOMING HOLIDAY WEEK. THEREFORE...THE
MAIN CONCERNS DURING THE LONG TERM PERIOD WILL FOCUS AROUND THE
CHANCES AND TIMING OF RAINFALL MONDAY INTO TUESDAY...THEN THE
POTENTIAL FOR A SIGNIFICANT WINTER STORM SOMEWHERE ACROSS THE GREAT
LAKES REGION INTO CHRISTMAS EVE.

A VERY IMPRESSIVE NORTHERN PACIFIC JET STREAK IS EXPECTED TO DEVELOP
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST BY EARLY SUNDAY...THEN
BEGIN TO DIG A SIGNIFICANT UPPER LEVEL TROUGH ACROSS THE CENTRAL
CONS BY MID WEEK. MODEL GUIDANCE CONTINUES IN GOOD AGREEMENT IN
TRACKING AN INITIAL AREA OF LOW PRESSURE EASTWARD FROM THE NORTHERN
HIGH PLAINS TO THE UPPER MISSISSIPPI VALLEY BY TUESDAY. THIS WOULD
KEEP ALL OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA IN THE WARM
SECTOR THROUGH EARLY TUESDAY...THUS ASIDE FROM A SMALL POSSIBILITY OF
THE PRECIP BEGINNING AS A MIX OF SLEET AND RAIN AT ONSET  EARLY
MONDAY...IT APPEARS THAT WE WILL BE IN FOR A RAIN EVENT ACROSS THE
ENTIRE AREA MONDAY AFTERNOON INTO MONDAY NIGHT.

THINGS BEGIN TO GET REALLY TRICKY LATE TUESDAY AND INTO CHRISTMAS
EVE...AS MODEL GUIDANCE IS INSTANT IN SECONDARY VORT MAX DIGGING
SOUTH AND ACROSS THE LOWER MISSISSIPPI VALLEY BY TUESDAY
NIGHT...LEADING TO A VERY AMPLIFIED AND INCREASING NEGATIVELY TILTED
UPPER TROUGH ACROSS THE CENTRAL CONUS. THIS IS A CLASSIC UPPER LEVEL
PATTERN SUPPORTIVE OF TREMENDOUS ATMOSPHERIC DYNAMICS AND HENCE
RAPID AND DEEP CYCLOGENESIS...SOMEWHERE ACROSS THE GREAT LAKES
REGION. IN FACT...THIS COULD RESULT IN "BOMB CYCLOGENESIS"...WHICH IS
DEFINED AS A DEEPENING RATE OF THE LOWS CENTRAL PRESSURE OF 24 MB IN
AS MANY HOURS. MODEL GUIDANCE CONTINUES TO BE IN SOME DISAGREEMENT IN
WHERE EXACTLY THIS STORM SYSTEM WILL TRACK INTO CHRISTMAS EVE.
HOWEVER...SUPPORT IS IN PLACE TO SUGGEST A GOOD POTENTIAL OF A
STRONG STORM SYSTEM ACROSS THE REGION DURING THIS PERIOD.
UNFORTUNATELY...THE ACTUAL TRACK OF THE STORM WILL BE THE DIFFERENCE
IN IF WE END UP WITH LITTLE OR NO SNOW...OR A SIGNIFICANT WINTER
STORM ACROSS THE AREA. THE LIKELIHOOD OF VERY STRONG WINDS WITH SUCH A
DEEP LOW COULD ALSO RESULT IN SIGNIFICANT BLOWING SNOW...IF IT DOES
OF COURSE SNOW THIS FAR WEST. THEREFORE...THIS STORM BEARS
SIGNIFICANT ATTENTION IN THE COMING DAYS.

FOLLOWING THIS SYSTEM...YET ANOTHER STORM SYSTEM COULD TAKE AIM ON
THE AREA BY FRIDAY. HOWEVER...UNCERTAINTY WITH THIS STORM IS
EXTREMELY HIGH...GIVEN THAT THE ACTUAL EVOLUTION OF THE FIRST STORM
SYSTEM WILL NEED TO BE IRONED OUT. OVERALL THOUGH IT LOOKS LIKE WE
ARE ENTERING INTO AN ACTIVE WEATHER PERIOD THROUGH THE REST OF THE
FORECAST PERIOD.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200930
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
330 AM CST Sat Dec 20 2014

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be inbetween strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1118 PM CST FRI DEC 19 2014

VFR conditions will begin the TAF period for most of the TAF
sites...with the exception being CMI where MVFR VIS is already in
place. Some of the issues with the TAFs tonight are the timing of
MVFR VIS and lowering CIGs. The surface high that was over
Illinois earlier is slowly pushing east with light to calm winds
remaining over much of central Illinois. Winds are also slowly
shifting to the east southeast allowing the low level moisture to
filter in both from the east and the west. Locations over Missouri
and Indiana have MVFR VIS and CIGs with locations in Missouri
under IFR CIGs. Given the complexity involved with timing of lower
VIS and CIGs...confidence is fairly low in the TAF forecast past
the first 6 hours. Currently have MVFR conditions over PIA
starting at 09Z...at 08Z for BMI and DEC...and at 12Z for SPI.
Mainly went with the HRRR since it seemed to have a pretty good
handle on the previous forecast. Also included a TEMPO group for
CMI as all guidance had IFR VIS over the site between 09Z and 13Z.
Only included a TEMPO for now since confidence in the timing is
lower. VFR conditions could resume around 16Z for the sites after
the next upper level wave moves through Illinois...but this could
change with the next TAF issuance.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...ALW






000
FXUS63 KILX 200930
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
330 AM CST Sat Dec 20 2014

.SHORT TERM...(Today)
ISSUED AT 329 AM CST SAT DEC 20 2014

Latest satellite data indicating a shortwave trof near Omaha which
is expected to push across our area later this morning. Upstream
surface observations across central and east central Iowa have had
some reports of some very light freezing drizzle and flurries to the
east of the main area of lift, with even some very light flurries
reported this past hour in St. Louis. A secondary shortwave was
noted over parts of southern Missouri into the lower Ohio Valley
that has produced a band of light snow which extended along and
south of the I-70 corridor early this morning. That system will
shift off to our east over the next few hours taking the light snow
out of southeast Illinois by dawn.

As the compact shortwave over the Missouri Valley tracks across the
area, many of the forecast soundings are not showing much in the way
of support for widespread precip as high pressure at the surface is
still holding firm over east central Illinois this morning. We see
moisture in the 850-800 mb layer over most of the area with not a
great deal above that until later this morning when the main area of
lift associated with the vort max swings thru. Much of the stratus/low
level moisture will remain to our west thru the morning as well before
tracking slowing into west central Illinois this afternoon. Will carry
chances for flurries this morning, mainly over west central Illinois
ahead of the vort max, as we see some mid level moisture/lift track
just to the west of our forecast area. Most of the short term high
resolution models continue to suggest as the shortwave moves across
the remainder of the state, moisture profiles will not support much
in the way of precip further east this afternoon. Despite the more
widespread cloud cover over our area today, we should see afternoon
temperatures a few degrees warmer than yesterday with readings
ranging from the mid 30s north to around 40 south.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 329 AM CST SAT DEC 20 2014

Fairly quiet weather expected tonight through Sunday night across
central and southeast IL as surface ridge shifts east into New
England and the mid Atlantic states Sunday. Temps to gradually
modify next few days with increasing southerly flow especially by
Monday. Added patchy drizzle/freezing drizzle to the IL river valley
overnight with the low clouds as surface temps are close to
freezing. Mostly cloudy skies expected Sunday with more low clouds
prevailing over northern counties. Highs in the lower 40s Sunday
which will be a bit above normal highs in the mid to upper 30s.
Added slight chance of light rain late Sunday night around Galesburg
with best rain chances arriving during the day Monday especially by
Monday afternoon NW areas and Monday night into Tue across area.
Strong low pressure near Pacific NW to track into MN Monday night
and increase chances of rain over IL ahead of approaching low
pressure and cold front. Milder highs in the 40s Monday and Tue with
Lawrenceville around 50F.

Forecast models then deepen another area of low pressure from the
southern plains into KY by dawn Wed and then into eastern lower MI
or just east of there by sunset Wed. Colder air to be drawn into IL
Tue night and Wed with rain changing to snow during Tue night and
continue good chances of light snow Wed. Could be some light snow
accumulations overnight Tue night into Wed especially over
eastcentral IL. Windy conditions expected Wed and Wed night as
deepening low pulls away with strong west winds gusting 25-35 mph.

Dry conditions expected on Christmas Day over the state as IL will
be inbetween strong low pressure exiting into eastern Canada and new
low pressure developing over Texas Panhandle by sunset Thu. This low
pressure ejects ne into the western Great Lakes by sunset Friday and
returns good chances of precipitation with southeast IL mainly rain
and a mix of rain/snow over central IL. Extended models show active
weather pattern looks to continue beyond day 7.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1118 PM CST FRI DEC 19 2014

VFR conditions will begin the TAF period for most of the TAF
sites...with the exception being CMI where MVFR VIS is already in
place. Some of the issues with the TAFs tonight are the timing of
MVFR VIS and lowering CIGs. The surface high that was over
Illinois earlier is slowly pushing east with light to calm winds
remaining over much of central Illinois. Winds are also slowly
shifting to the east southeast allowing the low level moisture to
filter in both from the east and the west. Locations over Missouri
and Indiana have MVFR VIS and CIGs with locations in Missouri
under IFR CIGs. Given the complexity involved with timing of lower
VIS and CIGs...confidence is fairly low in the TAF forecast past
the first 6 hours. Currently have MVFR conditions over PIA
starting at 09Z...at 08Z for BMI and DEC...and at 12Z for SPI.
Mainly went with the HRRR since it seemed to have a pretty good
handle on the previous forecast. Also included a TEMPO group for
CMI as all guidance had IFR VIS over the site between 09Z and 13Z.
Only included a TEMPO for now since confidence in the timing is
lower. VFR conditions could resume around 16Z for the sites after
the next upper level wave moves through Illinois...but this could
change with the next TAF issuance.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SHORT TERM...Smith
LONG TERM...07
AVIATION...ALW







000
FXUS63 KLOT 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014


...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
COMING SOON.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200903
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
303 AM CST SAT DEC 20 2014


...SHORT TERM...TODAY THROUGH SUNDAY...
302 AM CST

THE MAIN CONCERNS DURING THE SHORT TERM WILL BE WILL BE CENTERED
AROUND THE POTENTIAL FOR SOME FREEZING DRIZZLE ACROSS PORTIONS OF
NORTHERN ILLINOIS LATE TONIGHT INTO EARLY SUNDAY MORNING.

SURFACE HIGH PRESSURE CONTINUES TO BE IN PLACE ACROSS THE GREAT
LAKES REGION EARLY THIS MORNING. HOWEVER...ATTENTION FOR TODAY IS
FOCUSED ON A MID LEVEL DISTURBANCE...CURRENTLY NOTED IN THE WATER
VAPOR IMAGERY ACROSS SOUTHWESTERN IOWA. THIS DISTURBANCE WILL SHIFT
EASTWARD ACROSS CENTRAL AND NORTHERN ILLINOIS THROUGH EARLY THIS
AFTERNOON. OVERALL...MODEL SOUNDINGS DO NOT APPEAR ALL THAT
FAVORABLE FOR ANY LIGHT SNOW. HOWEVER...THERE HAVE BEEN SOME REPORTS
OF LIGHT FLURRIES ACROSS IOWA EARLY THIS MORNING...SO I HAVE OPTED
TO KEEP THE MENTION OF SOME FLURRIES GOING ACROSS THE AREA THROUGH
EARLY AFTERNOON.

WARM AIR ADVECTION/ISENTROPIC ASCENT WILL INCREASE
ACROSS MUCH OF THE MIDWEST AND GREAT LAKES REGION LATER TONIGHT INTO
SUNDAY MORNING IN RESPONSE TO AN INCREASING SOUTHERLY WIND FIELD
AHEAD OF A DEVELOPING STORM SYSTEM ACROSS THE NORTHERN HIGH PLAINS.
IT APPEARS THAT THIS WARM AIR ADVECTION WILL BE ENOUGH TO RESULT IN
THE DEVELOPMENT OF SOME FREEZING DRIZZLE OR LIGHT SNOW. MODEL
SOUNDINGS...ESPECIALLY FROM THE NAM SUGGEST CLOUD HEIGHTS WILL ONLY
REACH TO AROUND -7 DEGREES CELSIUS...SUGGESTING THE POSSIBILITY OF A
DEARTH OF ICE CRYSTALS IN THE CLOUDS. AS SUCH...THIS INCREASES THE
THREAT FOR FREEZING DRIZZLE VERSES LIGHT SNOW. OVERALL...THIS WILL
BE A VERY LIGHT EVENT...AND APPEARS TO MAINLY BE CONFINED ACROSS
NORTH CENTRAL ILLINOIS...THOUGH PORTIONS OF THE CHICAGO AREA COULD
ALSO EXPERIENCE SOME. THE PRIMARY TIMING FOR THIS ACTIVE LOOKS TO
BE AFTER MIDNIGHT TONIGHT THROUGH AROUND MID MORNING ON SUNDAY.
THEREAFTER...SURFACE TEMPERATURES SHOULD WARM ABOVE FREEZING ENDING
THE THREAT OF FREEZING PRECIP.

KJB

&&

.LONG TERM...
COMING SOON.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200738
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 AM CST SAT DEC 20 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200738
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 AM CST SAT DEC 20 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200738
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 AM CST SAT DEC 20 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200738
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
138 AM CST SAT DEC 20 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
137 AM CST

THE MAIN MARINE FORECAST CONCERNS THIS MORNING FOCUS ON A COUPLE OF
PERIODS OF STRONG WINDS OVER THE NEXT SEVERAL DAYS...SOUTH AND
SOUTHEAST WINDS 25-30 KT DEVELOPING SUNDAY AND CONTINUING THROUGH
MONDAY EVENING...THEN THE POTENTIAL FOR WEST HIGH GALES LATE
WEDNESDAY THROUGH THURSDAY...CHRISTMAS EVE AND CHRISTMAS DAY.

IN THE NEAR TERM...WEATHER IS QUITE TRANQUIL ACROSS LAKE MICHIGAN
THIS MORNING AS DIFFUSE HIGH PRESSURE WAS DRIFTING SLOWLY EAST
ACROSS THE REGION. THE RIDGE AXIS WILL SHIFT EAST OF THE LAKE THIS
AFTERNOON ALLOWING CURRENT VARIABLE WINDS TO BECOME SOUTHERLY. SOUTH
WINDS WILL GRADUALLY INCREASE LATE TONIGHT AND SUNDAY AS AN AREA OF
LOW PRESSURE DEVELOPS SOUTHEAST IN THE LEE OF THE NORTHERN ROCKIES
WITH A CORRESPONDING TIGHTENING OF THE SURFACE PRESSURE GRADIENT
BETWEEN THE LOW AND THE HIGH TO EAST OF THE LAKES. MODEL FORECAST
SOUNDINGS SUPPORT WINDS 20-25 KT SUNDAY AFTERNOON INCREASING TO 30
KT SUNDAY NIGHT/MONDAY...BECOMING A BIT MORE SOUTHEAST LATE MONDAY
AS THE SURFACE LOW MOVES INTO THE UPPER MIDWEST.

THE SURFACE LOW IS EXPECTED TO FILL A BIT ACROSS THE REGION TUESDAY
AS IT OCCLUDES. MODEL FORECASTS CONTINUE TO DEPICT A COMPLEX
EVOLUTION BY MID-WEEK HOWEVER...WITH A SECOND AREA OF LOW PRESSURE
FARTHER SOUTH ALONG THE COLD FRONT DEEPENING AND WRAPPING NORTHWARD
INTO THE GREAT LAKES WEDNESDAY AND THURSDAY. SPREAD REMAINS AMONGST
MODEL FORECASTS OF THE EXACT TRACK AND DEPTH OF THIS LOW...BUT IT
DOES APPEAR THAT A DEEPENING SUB-980 MB LOW WILL TRACK NORTH ACROSS
THE GREAT LAKES REGION CHRISTMAS EVE INTO CHRISTMAS DAY. SUCH A LOW
PASSING EAST OF LAKE MICHIGAN SUPPORTS THE POTENTIAL FOR THE
DEVELOPMENT OF WESTERLY GALES ON THE LAKE...PERHAPS HIGH GALES ABOVE
40 KT...FROM WEDNESDAY AFTERNOON OR EVENING THROUGH THE DAY
THURSDAY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200555
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1155 PM CST FRI DEC 19 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
200 PM CST

HIGH PRESSURE IS OVER THE REGION AND IT WILL SLOWLY SHIFT EAST
THROUGH SUNDAY NIGHT. LIGHT WINDS BECOME SOUTHWEST OVERNIGHT. THE
NEXT LOW MOVES OVER THE DAKOTAS SUNDAY NIGHT WITH SOUTH WINDS
INCREASING TO 30 KT.  MODELS DISAGREE WITH EXACT PATH OF THIS LOW.
ONE HAS THE LOW DEEPENING OVER LAKE SUPERIOR WEDNESDAY WHILE ANOTHER
HAS THE LOW DEEPENING OVER LAKE ERIE.  SOUTHEAST WINDS AROUND 25 KT
ARE EXPECTED THROUGH MONDAY NIGHT AHEAD OF THE LOW...THEN WINDS
BECOME WEST BEHIND IT.  FOR SPEEDS WENT MIDDLE OF THE ROAD GIVEN THE
VARIABILITY.  COULD DEFINITELY SEE HIGHER GUSTS IF THE LOW DEEPENS
CLOSER TO THE LAKE.

MODELS AGREE ON VERY STRONG WINDS BEHIND THE LOW WEDNESDAY NIGHT
THROUGH THURSDAY.  HAVE HIGH END GALES IN THE FORECAST AND SOME
GUIDANCE MEMBERS SUGGEST LOW END STORM FORCE GUSTS MAY BE POSSIBLE.
DO NOT HAVE THE CONFIDENCE TO GO THAT HIGH JUST YET...BUT HAVE HIGH
CONFIDENCE IN AT LEAST GALES.  THE LOW SHIFTS NORTHEAST WITH WINDS
DIMINISHING THURSDAY NIGHT. THE NEXT LOW HOWEVER MOVES OVER THE
SOUTHERN PLAINS THURSDAY EVENING.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200555
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1155 PM CST FRI DEC 19 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
200 PM CST

HIGH PRESSURE IS OVER THE REGION AND IT WILL SLOWLY SHIFT EAST
THROUGH SUNDAY NIGHT. LIGHT WINDS BECOME SOUTHWEST OVERNIGHT. THE
NEXT LOW MOVES OVER THE DAKOTAS SUNDAY NIGHT WITH SOUTH WINDS
INCREASING TO 30 KT.  MODELS DISAGREE WITH EXACT PATH OF THIS LOW.
ONE HAS THE LOW DEEPENING OVER LAKE SUPERIOR WEDNESDAY WHILE ANOTHER
HAS THE LOW DEEPENING OVER LAKE ERIE.  SOUTHEAST WINDS AROUND 25 KT
ARE EXPECTED THROUGH MONDAY NIGHT AHEAD OF THE LOW...THEN WINDS
BECOME WEST BEHIND IT.  FOR SPEEDS WENT MIDDLE OF THE ROAD GIVEN THE
VARIABILITY.  COULD DEFINITELY SEE HIGHER GUSTS IF THE LOW DEEPENS
CLOSER TO THE LAKE.

MODELS AGREE ON VERY STRONG WINDS BEHIND THE LOW WEDNESDAY NIGHT
THROUGH THURSDAY.  HAVE HIGH END GALES IN THE FORECAST AND SOME
GUIDANCE MEMBERS SUGGEST LOW END STORM FORCE GUSTS MAY BE POSSIBLE.
DO NOT HAVE THE CONFIDENCE TO GO THAT HIGH JUST YET...BUT HAVE HIGH
CONFIDENCE IN AT LEAST GALES.  THE LOW SHIFTS NORTHEAST WITH WINDS
DIMINISHING THURSDAY NIGHT. THE NEXT LOW HOWEVER MOVES OVER THE
SOUTHERN PLAINS THURSDAY EVENING.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200555
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1155 PM CST FRI DEC 19 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
200 PM CST

HIGH PRESSURE IS OVER THE REGION AND IT WILL SLOWLY SHIFT EAST
THROUGH SUNDAY NIGHT. LIGHT WINDS BECOME SOUTHWEST OVERNIGHT. THE
NEXT LOW MOVES OVER THE DAKOTAS SUNDAY NIGHT WITH SOUTH WINDS
INCREASING TO 30 KT.  MODELS DISAGREE WITH EXACT PATH OF THIS LOW.
ONE HAS THE LOW DEEPENING OVER LAKE SUPERIOR WEDNESDAY WHILE ANOTHER
HAS THE LOW DEEPENING OVER LAKE ERIE.  SOUTHEAST WINDS AROUND 25 KT
ARE EXPECTED THROUGH MONDAY NIGHT AHEAD OF THE LOW...THEN WINDS
BECOME WEST BEHIND IT.  FOR SPEEDS WENT MIDDLE OF THE ROAD GIVEN THE
VARIABILITY.  COULD DEFINITELY SEE HIGHER GUSTS IF THE LOW DEEPENS
CLOSER TO THE LAKE.

MODELS AGREE ON VERY STRONG WINDS BEHIND THE LOW WEDNESDAY NIGHT
THROUGH THURSDAY.  HAVE HIGH END GALES IN THE FORECAST AND SOME
GUIDANCE MEMBERS SUGGEST LOW END STORM FORCE GUSTS MAY BE POSSIBLE.
DO NOT HAVE THE CONFIDENCE TO GO THAT HIGH JUST YET...BUT HAVE HIGH
CONFIDENCE IN AT LEAST GALES.  THE LOW SHIFTS NORTHEAST WITH WINDS
DIMINISHING THURSDAY NIGHT. THE NEXT LOW HOWEVER MOVES OVER THE
SOUTHERN PLAINS THURSDAY EVENING.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200555
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1155 PM CST FRI DEC 19 2014

.SHORT TERM...
237 PM CST

THROUGH SATURDAY...

UNFORTUNATELY IT LOOKS LIKE WE WILL REMAIN LOCKED IN THE CLOUDS YET
AGAIN TONIGHT...DESPITE A CLEARING WEDGE THAT EXTENDS FROM
WESTCENTRAL IL TO SOUTHERN IN. WITH HIGH PRESSURE OVERHEAD THE
ABILITY TO MIX TO THE SFC DRIER AIR HAS BEEN NONEXISTENT. WITH THE
CONSIDERABLE SOLAR SHIELDING THIS AFTERNOON...SFC TEMPS HAVE BEEN
UNABLE TO WARM MUCH. TEMPS IN MOST LOCATIONS HAVE REMAINED ARND 30
TO A FEW LOW 30S ACROSS THE FAR SOUTHERN CWFA. OVERNIGHT THE SFC
RIDGE WILL DRIFT EAST...ALLOWING LGT/VRB WINDS TO SLOWLY TURN
SOUTHWESTERLY BY DAYBREAK SAT. OVERNIGHT LOWS WILL GENERALLY BE IN
THE LOW/MID 20S...BUT IF CLOUDS REMAIN THICK ENOUGH IT IS PLAUSIBLE
THAT TEMPS COULD HOLD IN THE MID/UPR 20S. GUIDANCE HAS INDICATED A
WEAK LOBE OF VORTICITY ALONG THE NORTHERN STREAM PUSHING EAST ACROSS
THE NORTHERN PLAINS OVERNIGHT...ARRIVING ACROSS THE GREAT LAKES
REGION AROUND SAT MORNING. WHILE IT APPEARS MOST OF THE NEAR SFC
WILL REMAIN DRY...THERE IS SOME WEAK FORCING IN THE MID-LVLS ALONG
WITH MARGINAL SATURATION THAT SOME FLURRIES COULD OCCUR DURING THE
MORNING HOURS. WITH YET ANOTHER DAY OF CONTINUED CLOUDINESS SAT...IT
APPEARS LESS FAVORABLE FOR ANY BUMP TO THE TEMPS. SO HAVE NUDGED
TEMPS DOWN A DEGREE TO THE MID 30S ACROSS THE CWFA.

SATURDAY NIGHT WILL GENERALLY REMAIN DRY...HOWEVER THERE IS ANOTHER
WEAK VORT TRYING TO LIFT NORTHEAST ACROSS IOWA LATE SAT NGT/EARLY
SUN. WITH A SLIGHT WARM LAYER TRYING TO LIFT ACROSS THE
REGION...HOWEVER HAVE HELD ONTO MAINLY LGT SNOW. THERE IS SOME
CONCERN THAT TEMPS ALOFT COULD BE WARM ENOUGH TO FULLY MELT ANY
DENDRITES. THE OTHER CONCERN WORTH MENTIONING IS THAT THE LIFT/OMEGA
IS LACKING LATE SAT NGT...SO DROPLET SIZE COULD BE SMALL AND INSTEAD
OF ANY DENDRITES THERE COULD END UP BEING PATCHY FREEZING
DRIZZLE...MAINLY AFTER MIDNIGHT.

BEACHLER

&&

.LONG TERM...
237 PM CST

SUNDAY THROUGH SATURDAY...

500MB TROUGH WILL BEGIN TO DIG SOUTH ACROSS THE CENTRAL CONUS SUN
INTO MON...WITH A SERIES OF MID-LVL VORTS PROGGED TO SLIDE SOUTHEAST
ACROSS THE CANADIAN ROCKIES INTO THE NORTHERN PLAINS. THE MAIN FOCUS
WILL BE ON A STRONGER SHORTWAVE DEVELOPING SUN NGT/EARLY MON ACROSS
THE DAKOTAS...EXPECTED TO SLIDE SOUTHEAST ACROSS NORTHERN IL.
ALTHOUGH CONFIDENCE IN THE TIMING/PLACEMENT OF THIS PATH IS LOW
GIVEN CONTINUED CORRECTIONS BASED ON THE LATEST GUIDANCE CYCLES.

MOISTURE WILL BE ADVECTING NORTH OF THIS LOW MON...WITH PRECIP
ARRIVING MON MORNING LIKELY AS MAINLY RAIN OR PERHAPS A RAIN/SNOW
MIX ACROSS THE NORTHERN CWFA. THEN A QUICK PUSH OF MUCH WARMER AIR
WILL BRING TEMPS INTO THE UPR 30S/NEAR 40 MON AFTN AND SHOULD TURN
ANY PRECIP TO PLAIN RAIN. AS MON NGT PROGRESSES...THE LOW IS PROGGED
TO STEADILY DEEPEN AND LIFT NORTHEAST ACROSS NORTHERN IL EARLY TUE.
FROPA CURRENTLY PROGGED FOR TUE EVE...BRINGING COLDER AIR BACK INTO
THE FORECAST AREA AND TURNING RAIN OVER TO LGT SNOW.

MON NGT WITH THE WARM AIR STEADILY ADVECTING NORTH...TEMPS WILL
REMAIN IN THE MID/UPR 30S. TUE TEMPS COULD PUSH EVEN
WARMER...DEPENDING ON THE PLACEMENT/TIMING OF FROPA. CURRENT
INDICATIONS ARE THAT TEMPS WILL PUSH INTO THE LOW/MID 40S TUE AFTN.

CHRISTMAS EVE THROUGH CHRISTMAS DAY...
ENSEMBLES ALONG WITH OPERATIONAL SOLUTIONS HAVE BEEN TARGETING THE
SYSTEM BECOMING WRAPPED UP OVER THE GREAT LAKES REGION AND POSSIBLY
TRANSITIONING INTO ANOTHER LOW OVER SOUTHERN ONTARIO/SOUTHWEST
QUEBEC CHRISTMAS DAY. A TIGHT GRADIENT WILL REMAIN OVER THE REGION
BOTH CHRISTMAS EVE/CHRISTMAS DAY...WITH TEMPS RETURNING TO MORE
SEASONAL CONDITIONS IN THE LOW/MID 30S.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CEILINGS LIKELY BECOMING VFR BEFORE SUNRISE. EXPECTED TO
  LOWER TO MVFR AGAIN THIS EVENING.

* LIGHT/VARIABLE WINDS BECOMING LIGHT SOUTH-SOUTHWEST BY MIDDAY.

RATZER

//DISCUSSION...UPDATED 06Z...

WEAK SURFACE HIGH PRESSURE RIDGE MOVING SLOWLY EAST ACROSS THE
AREA THIS MORNING. CALM OR LIGHT/VARIABLE WINDS AND MVFR CLOUDS
TRAPPED BENEATH SHALLOW INVERSION PERSISTING. SURFACE OBS INDICATE
MVFR CEILINGS ERODING FROM THE SOUTHWEST HOWEVER...WITH THE
POTENTIAL FOR CONDITIONS TO BECOME VFR AT TAF SITES DURING THE
PRE-DAWN HOURS. QUESTION IS HOW LONG VFR LASTS...AS EXTENSIVE AREA
OF MVFR/IFR CEILINGS WEST OF THE MISSISSIPPI RIVER WILL EVENTUALLY
SPREAD INTO THE AREA TONIGHT. KRFD BEING FARTHER WEST LOOKS TO BE
BACK INTO MVFR CONDITIONS PERHAPS AS EARLY AS MID-LATE MORNING.
CEILINGS WILL LIKELY LOWER INTO IFR RANGE LATE THIS EVENING INTO
EARLY SUNDAY...WITH THE POTENTIAL FOR SOME FLURRIES OR FREEZING
DRIZZLE DEVELOPING SUNDAY MORNING.

CALM OR LIGHT/VARIABLE WINDS LESS THAN 5 KT WILL BECOME SOUTH-
SOUTHWEST AT 5 KT BY EARLY AFTERNOON AND REMAIN LIGHT SOUTH
THROUGH TONIGHT.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM IN CEILING TRENDS AND VFR DURATION TODAY.

* HIGH IN WIND TRENDS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS.  SOUTH WINDS.

MONDAY...MVFR CIGS. BRIEF PERIOD OF RAIN OR MIXED RAIN AND SNOW.

TUESDAY...MVFR CIGS. CHANCE OF RAIN.

WEDNESDAY...MVFR CIGS. BLUSTERY - GUSTY WEST WINDS. CHANCE OF
SNOW.

THURSDAY...VFR.

ED F

&&

.MARINE...
200 PM CST

HIGH PRESSURE IS OVER THE REGION AND IT WILL SLOWLY SHIFT EAST
THROUGH SUNDAY NIGHT. LIGHT WINDS BECOME SOUTHWEST OVERNIGHT. THE
NEXT LOW MOVES OVER THE DAKOTAS SUNDAY NIGHT WITH SOUTH WINDS
INCREASING TO 30 KT.  MODELS DISAGREE WITH EXACT PATH OF THIS LOW.
ONE HAS THE LOW DEEPENING OVER LAKE SUPERIOR WEDNESDAY WHILE ANOTHER
HAS THE LOW DEEPENING OVER LAKE ERIE.  SOUTHEAST WINDS AROUND 25 KT
ARE EXPECTED THROUGH MONDAY NIGHT AHEAD OF THE LOW...THEN WINDS
BECOME WEST BEHIND IT.  FOR SPEEDS WENT MIDDLE OF THE ROAD GIVEN THE
VARIABILITY.  COULD DEFINITELY SEE HIGHER GUSTS IF THE LOW DEEPENS
CLOSER TO THE LAKE.

MODELS AGREE ON VERY STRONG WINDS BEHIND THE LOW WEDNESDAY NIGHT
THROUGH THURSDAY.  HAVE HIGH END GALES IN THE FORECAST AND SOME
GUIDANCE MEMBERS SUGGEST LOW END STORM FORCE GUSTS MAY BE POSSIBLE.
DO NOT HAVE THE CONFIDENCE TO GO THAT HIGH JUST YET...BUT HAVE HIGH
CONFIDENCE IN AT LEAST GALES.  THE LOW SHIFTS NORTHEAST WITH WINDS
DIMINISHING THURSDAY NIGHT. THE NEXT LOW HOWEVER MOVES OVER THE
SOUTHERN PLAINS THURSDAY EVENING.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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 200535
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1135 PM CST Fri Dec 19 2014

.UPDATE...
ISSUED AT 905 PM CST FRI DEC 19 2014

The surface ridge axis is finally making some progress to the east
of Illinois, allowing winds west of I-55 to start a trend out of
the southeast. A weak shortwave passing across southern IL could
trigger some light snow showers or flurries southeast of I-70.
Radar returns toward Lawrenceville are mostly virga, with no snow
reaching the ground yet. Cloud heights are lowering with time
under that wave, so some flurries were added to the forecast for
the far southeast counties toward midnight.

The next area of concern is NW of the IL river, where low clouds
and fog may develop into some freezing drizzle toward sunrise. The
precip could fall as flurries, but a lack of ice crystals to feed
into the low cloud layer will limit the ability for snowflakes to
develop. Thus, the concern for FZDZ to occur. Any icing would
cause slippery travel conditions. Have added a mention of FZDZ
between 12z-15z Sat morn, but may need a mention even earlier
depending on speed of saturation and progression of shortwave from
Nebraska across Iowa/N MO.

Low temps will not drop off appreciably from current temps due to
increasing clouds. Updates this evening were to the weather and
sky grids to match expected trends.

&&

.SHORT TERM...(Tonight)
ISSUED AT 328 PM CST FRI DEC 19 2014

20z/2pm visible satellite imagery continues to show a large break in
the overcast extending from southeast Iowa across much of central
Illinois into Kentucky. With high pressure directly overhead and
only very light low-level winds, partly to mostly clear conditions
will persist through the evening hours.  As the high begins to shift
eastward, a southerly return flow will gradually develop late
tonight into Saturday, allowing the low clouds currently across
Iowa/Missouri to spill back into the area.  End result will be a
mostly clear start to the night, with overcast conditions expected
across the board by dawn Saturday.  May also see some patchy fog
west of the I-55 corridor late tonight as low-level moisture
increases, but am not expecting any major restrictions to
visibility.  Due to the initially mostly clear skies and light
winds, another cold night is expected with low temperatures
bottoming out in the lower to middle 20s.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 328 PM CST FRI DEC 19 2014

A rather quiet weekend is on tap across central and southeast
Illinois, but weather activity will be on the upswing heading into
the Holiday work week.

Model agreement is good through the weekend with mostly neutral
upper-level flow and high pressure expected to be the dominant
player at the surface. A week wave, currently pushing east across
the central Plains, will cross the area early Saturday. However, the
forcing appears too weak, and moisture depth too shallow, to warrant
a mention of any precipitation.

A strong, slow moving system will impact the area from Monday into
Christmas Eve. We will remain on the warm side of the system through
Tuesday, with all precipitation initially expected to fall in the
form of rain. Temperatures ahead of the system will also average
nearly 10 degrees above normal for late December.

The colder air on the back side of the deepening storm system will
arrive for Tuesday night into Christmas Eve. This would support any
remaining precipitation changing over to snow. At this point, the
threat for significant snowfall on the back side of the system seems
low, but some light snow accumulation is likely. The model
agreement/run-to-run consistency is still a little shaky heading
into midweek, so future model trends will need to be monitored very
closely.

Another system is progged to arrive by late in the week, generally
Friday into Saturday. However, model consistency with this system is
poorer than the first, so confidence in the ultimate outcome is not
very high.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1118 PM CST FRI DEC 19 2014

VFR conditions will begin the TAF period for most of the TAF
sites...with the exception being CMI where MVFR VIS is already in
place. Some of the issues with the TAFs tonight are the timing of
MVFR VIS and lowering CIGs. The surface high that was over
Illinois earlier is slowly pushing east with light to calm winds
remaining over much of central Illinois. Winds are also slowly
shifting to the east southeast allowing the low level moisture to
filter in both from the east and the west. Locations over Missouri
and Indiana have MVFR VIS and CIGs with locations in Missouri
under IFR CIGs. Given the complexity involved with timing of lower
VIS and CIGs...confidence is fairly low in the TAF forecast past
the first 6 hours. Currently have MVFR conditions over PIA
starting at 09Z...at 08Z for BMI and DEC...and at 12Z for SPI.
Mainly went with the HRRR since it seemed to have a pretty good
handle on the previous forecast. Also included a TEMPO group for
CMI as all guidance had IFR VIS over the site between 09Z and 13Z.
Only included a TEMPO for now since confidence in the timing is
lower. VFR conditions could resume around 16Z for the sites after
the next upper level wave moves through Illinois...but this could
change with the next TAF issuance.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...ALW







000
FXUS63 KILX 200535
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1135 PM CST Fri Dec 19 2014

.UPDATE...
ISSUED AT 905 PM CST FRI DEC 19 2014

The surface ridge axis is finally making some progress to the east
of Illinois, allowing winds west of I-55 to start a trend out of
the southeast. A weak shortwave passing across southern IL could
trigger some light snow showers or flurries southeast of I-70.
Radar returns toward Lawrenceville are mostly virga, with no snow
reaching the ground yet. Cloud heights are lowering with time
under that wave, so some flurries were added to the forecast for
the far southeast counties toward midnight.

The next area of concern is NW of the IL river, where low clouds
and fog may develop into some freezing drizzle toward sunrise. The
precip could fall as flurries, but a lack of ice crystals to feed
into the low cloud layer will limit the ability for snowflakes to
develop. Thus, the concern for FZDZ to occur. Any icing would
cause slippery travel conditions. Have added a mention of FZDZ
between 12z-15z Sat morn, but may need a mention even earlier
depending on speed of saturation and progression of shortwave from
Nebraska across Iowa/N MO.

Low temps will not drop off appreciably from current temps due to
increasing clouds. Updates this evening were to the weather and
sky grids to match expected trends.

&&

.SHORT TERM...(Tonight)
ISSUED AT 328 PM CST FRI DEC 19 2014

20z/2pm visible satellite imagery continues to show a large break in
the overcast extending from southeast Iowa across much of central
Illinois into Kentucky. With high pressure directly overhead and
only very light low-level winds, partly to mostly clear conditions
will persist through the evening hours.  As the high begins to shift
eastward, a southerly return flow will gradually develop late
tonight into Saturday, allowing the low clouds currently across
Iowa/Missouri to spill back into the area.  End result will be a
mostly clear start to the night, with overcast conditions expected
across the board by dawn Saturday.  May also see some patchy fog
west of the I-55 corridor late tonight as low-level moisture
increases, but am not expecting any major restrictions to
visibility.  Due to the initially mostly clear skies and light
winds, another cold night is expected with low temperatures
bottoming out in the lower to middle 20s.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 328 PM CST FRI DEC 19 2014

A rather quiet weekend is on tap across central and southeast
Illinois, but weather activity will be on the upswing heading into
the Holiday work week.

Model agreement is good through the weekend with mostly neutral
upper-level flow and high pressure expected to be the dominant
player at the surface. A week wave, currently pushing east across
the central Plains, will cross the area early Saturday. However, the
forcing appears too weak, and moisture depth too shallow, to warrant
a mention of any precipitation.

A strong, slow moving system will impact the area from Monday into
Christmas Eve. We will remain on the warm side of the system through
Tuesday, with all precipitation initially expected to fall in the
form of rain. Temperatures ahead of the system will also average
nearly 10 degrees above normal for late December.

The colder air on the back side of the deepening storm system will
arrive for Tuesday night into Christmas Eve. This would support any
remaining precipitation changing over to snow. At this point, the
threat for significant snowfall on the back side of the system seems
low, but some light snow accumulation is likely. The model
agreement/run-to-run consistency is still a little shaky heading
into midweek, so future model trends will need to be monitored very
closely.

Another system is progged to arrive by late in the week, generally
Friday into Saturday. However, model consistency with this system is
poorer than the first, so confidence in the ultimate outcome is not
very high.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1118 PM CST FRI DEC 19 2014

VFR conditions will begin the TAF period for most of the TAF
sites...with the exception being CMI where MVFR VIS is already in
place. Some of the issues with the TAFs tonight are the timing of
MVFR VIS and lowering CIGs. The surface high that was over
Illinois earlier is slowly pushing east with light to calm winds
remaining over much of central Illinois. Winds are also slowly
shifting to the east southeast allowing the low level moisture to
filter in both from the east and the west. Locations over Missouri
and Indiana have MVFR VIS and CIGs with locations in Missouri
under IFR CIGs. Given the complexity involved with timing of lower
VIS and CIGs...confidence is fairly low in the TAF forecast past
the first 6 hours. Currently have MVFR conditions over PIA
starting at 09Z...at 08Z for BMI and DEC...and at 12Z for SPI.
Mainly went with the HRRR since it seemed to have a pretty good
handle on the previous forecast. Also included a TEMPO group for
CMI as all guidance had IFR VIS over the site between 09Z and 13Z.
Only included a TEMPO for now since confidence in the timing is
lower. VFR conditions could resume around 16Z for the sites after
the next upper level wave moves through Illinois...but this could
change with the next TAF issuance.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...ALW







000
FXUS63 KILX 200535
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1135 PM CST Fri Dec 19 2014

.UPDATE...
ISSUED AT 905 PM CST FRI DEC 19 2014

The surface ridge axis is finally making some progress to the east
of Illinois, allowing winds west of I-55 to start a trend out of
the southeast. A weak shortwave passing across southern IL could
trigger some light snow showers or flurries southeast of I-70.
Radar returns toward Lawrenceville are mostly virga, with no snow
reaching the ground yet. Cloud heights are lowering with time
under that wave, so some flurries were added to the forecast for
the far southeast counties toward midnight.

The next area of concern is NW of the IL river, where low clouds
and fog may develop into some freezing drizzle toward sunrise. The
precip could fall as flurries, but a lack of ice crystals to feed
into the low cloud layer will limit the ability for snowflakes to
develop. Thus, the concern for FZDZ to occur. Any icing would
cause slippery travel conditions. Have added a mention of FZDZ
between 12z-15z Sat morn, but may need a mention even earlier
depending on speed of saturation and progression of shortwave from
Nebraska across Iowa/N MO.

Low temps will not drop off appreciably from current temps due to
increasing clouds. Updates this evening were to the weather and
sky grids to match expected trends.

&&

.SHORT TERM...(Tonight)
ISSUED AT 328 PM CST FRI DEC 19 2014

20z/2pm visible satellite imagery continues to show a large break in
the overcast extending from southeast Iowa across much of central
Illinois into Kentucky. With high pressure directly overhead and
only very light low-level winds, partly to mostly clear conditions
will persist through the evening hours.  As the high begins to shift
eastward, a southerly return flow will gradually develop late
tonight into Saturday, allowing the low clouds currently across
Iowa/Missouri to spill back into the area.  End result will be a
mostly clear start to the night, with overcast conditions expected
across the board by dawn Saturday.  May also see some patchy fog
west of the I-55 corridor late tonight as low-level moisture
increases, but am not expecting any major restrictions to
visibility.  Due to the initially mostly clear skies and light
winds, another cold night is expected with low temperatures
bottoming out in the lower to middle 20s.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 328 PM CST FRI DEC 19 2014

A rather quiet weekend is on tap across central and southeast
Illinois, but weather activity will be on the upswing heading into
the Holiday work week.

Model agreement is good through the weekend with mostly neutral
upper-level flow and high pressure expected to be the dominant
player at the surface. A week wave, currently pushing east across
the central Plains, will cross the area early Saturday. However, the
forcing appears too weak, and moisture depth too shallow, to warrant
a mention of any precipitation.

A strong, slow moving system will impact the area from Monday into
Christmas Eve. We will remain on the warm side of the system through
Tuesday, with all precipitation initially expected to fall in the
form of rain. Temperatures ahead of the system will also average
nearly 10 degrees above normal for late December.

The colder air on the back side of the deepening storm system will
arrive for Tuesday night into Christmas Eve. This would support any
remaining precipitation changing over to snow. At this point, the
threat for significant snowfall on the back side of the system seems
low, but some light snow accumulation is likely. The model
agreement/run-to-run consistency is still a little shaky heading
into midweek, so future model trends will need to be monitored very
closely.

Another system is progged to arrive by late in the week, generally
Friday into Saturday. However, model consistency with this system is
poorer than the first, so confidence in the ultimate outcome is not
very high.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1118 PM CST FRI DEC 19 2014

VFR conditions will begin the TAF period for most of the TAF
sites...with the exception being CMI where MVFR VIS is already in
place. Some of the issues with the TAFs tonight are the timing of
MVFR VIS and lowering CIGs. The surface high that was over
Illinois earlier is slowly pushing east with light to calm winds
remaining over much of central Illinois. Winds are also slowly
shifting to the east southeast allowing the low level moisture to
filter in both from the east and the west. Locations over Missouri
and Indiana have MVFR VIS and CIGs with locations in Missouri
under IFR CIGs. Given the complexity involved with timing of lower
VIS and CIGs...confidence is fairly low in the TAF forecast past
the first 6 hours. Currently have MVFR conditions over PIA
starting at 09Z...at 08Z for BMI and DEC...and at 12Z for SPI.
Mainly went with the HRRR since it seemed to have a pretty good
handle on the previous forecast. Also included a TEMPO group for
CMI as all guidance had IFR VIS over the site between 09Z and 13Z.
Only included a TEMPO for now since confidence in the timing is
lower. VFR conditions could resume around 16Z for the sites after
the next upper level wave moves through Illinois...but this could
change with the next TAF issuance.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...ALW







000
FXUS63 KILX 200535
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1135 PM CST Fri Dec 19 2014

.UPDATE...
ISSUED AT 905 PM CST FRI DEC 19 2014

The surface ridge axis is finally making some progress to the east
of Illinois, allowing winds west of I-55 to start a trend out of
the southeast. A weak shortwave passing across southern IL could
trigger some light snow showers or flurries southeast of I-70.
Radar returns toward Lawrenceville are mostly virga, with no snow
reaching the ground yet. Cloud heights are lowering with time
under that wave, so some flurries were added to the forecast for
the far southeast counties toward midnight.

The next area of concern is NW of the IL river, where low clouds
and fog may develop into some freezing drizzle toward sunrise. The
precip could fall as flurries, but a lack of ice crystals to feed
into the low cloud layer will limit the ability for snowflakes to
develop. Thus, the concern for FZDZ to occur. Any icing would
cause slippery travel conditions. Have added a mention of FZDZ
between 12z-15z Sat morn, but may need a mention even earlier
depending on speed of saturation and progression of shortwave from
Nebraska across Iowa/N MO.

Low temps will not drop off appreciably from current temps due to
increasing clouds. Updates this evening were to the weather and
sky grids to match expected trends.

&&

.SHORT TERM...(Tonight)
ISSUED AT 328 PM CST FRI DEC 19 2014

20z/2pm visible satellite imagery continues to show a large break in
the overcast extending from southeast Iowa across much of central
Illinois into Kentucky. With high pressure directly overhead and
only very light low-level winds, partly to mostly clear conditions
will persist through the evening hours.  As the high begins to shift
eastward, a southerly return flow will gradually develop late
tonight into Saturday, allowing the low clouds currently across
Iowa/Missouri to spill back into the area.  End result will be a
mostly clear start to the night, with overcast conditions expected
across the board by dawn Saturday.  May also see some patchy fog
west of the I-55 corridor late tonight as low-level moisture
increases, but am not expecting any major restrictions to
visibility.  Due to the initially mostly clear skies and light
winds, another cold night is expected with low temperatures
bottoming out in the lower to middle 20s.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 328 PM CST FRI DEC 19 2014

A rather quiet weekend is on tap across central and southeast
Illinois, but weather activity will be on the upswing heading into
the Holiday work week.

Model agreement is good through the weekend with mostly neutral
upper-level flow and high pressure expected to be the dominant
player at the surface. A week wave, currently pushing east across
the central Plains, will cross the area early Saturday. However, the
forcing appears too weak, and moisture depth too shallow, to warrant
a mention of any precipitation.

A strong, slow moving system will impact the area from Monday into
Christmas Eve. We will remain on the warm side of the system through
Tuesday, with all precipitation initially expected to fall in the
form of rain. Temperatures ahead of the system will also average
nearly 10 degrees above normal for late December.

The colder air on the back side of the deepening storm system will
arrive for Tuesday night into Christmas Eve. This would support any
remaining precipitation changing over to snow. At this point, the
threat for significant snowfall on the back side of the system seems
low, but some light snow accumulation is likely. The model
agreement/run-to-run consistency is still a little shaky heading
into midweek, so future model trends will need to be monitored very
closely.

Another system is progged to arrive by late in the week, generally
Friday into Saturday. However, model consistency with this system is
poorer than the first, so confidence in the ultimate outcome is not
very high.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 1118 PM CST FRI DEC 19 2014

VFR conditions will begin the TAF period for most of the TAF
sites...with the exception being CMI where MVFR VIS is already in
place. Some of the issues with the TAFs tonight are the timing of
MVFR VIS and lowering CIGs. The surface high that was over
Illinois earlier is slowly pushing east with light to calm winds
remaining over much of central Illinois. Winds are also slowly
shifting to the east southeast allowing the low level moisture to
filter in both from the east and the west. Locations over Missouri
and Indiana have MVFR VIS and CIGs with locations in Missouri
under IFR CIGs. Given the complexity involved with timing of lower
VIS and CIGs...confidence is fairly low in the TAF forecast past
the first 6 hours. Currently have MVFR conditions over PIA
starting at 09Z...at 08Z for BMI and DEC...and at 12Z for SPI.
Mainly went with the HRRR since it seemed to have a pretty good
handle on the previous forecast. Also included a TEMPO group for
CMI as all guidance had IFR VIS over the site between 09Z and 13Z.
Only included a TEMPO for now since confidence in the timing is
lower. VFR conditions could resume around 16Z for the sites after
the next upper level wave moves through Illinois...but this could
change with the next TAF issuance.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...ALW







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