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000
FXUS63 KILX 270539
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1139 PM CST Thu Feb 26 2015

.UPDATE...
ISSUED AT 900 PM CST THU FEB 26 2015

Small area of clouds continues to slowly move south this evening.
Also, some isolated flurries are also still occurring under this
cloud cover. Expect this to continue, mainly in eastern areas of
the CWA. This will eventually clear up overnight. Current forecast
has a good handle on this and with temp trends the rest of the
night. No update planned at this time.

&&

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 1139 PM CST THU FEB 26 2015

VFR conditions will prevail at all TAF sites next 24hrs. Clouds
around 4.5kft are still effecting BMI/DEC/CMI late tonight but are
slowly moving southeast and should clear BMI and DEC by 06z, and
CMI by 09z. Will keep a 2hr TEMPO group for DEC and CMI just
because it seems these clouds are just lingering and will not go
quickly. Then clear skies should prevail remainder of the TAF
period. Winds will be northwest overnight and then become light
and variable tomorrow.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY until 10 AM CST Friday FOR ILZ027>031-
036>038-040>051-053-055-057.

&&

$$

UPDATE...Auten
SHORT TERM...07
LONG TERM...Goetsch
AVIATION...Auten







000
FXUS63 KILX 270539
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1139 PM CST Thu Feb 26 2015

.UPDATE...
ISSUED AT 900 PM CST THU FEB 26 2015

Small area of clouds continues to slowly move south this evening.
Also, some isolated flurries are also still occurring under this
cloud cover. Expect this to continue, mainly in eastern areas of
the CWA. This will eventually clear up overnight. Current forecast
has a good handle on this and with temp trends the rest of the
night. No update planned at this time.

&&

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
ISSUED AT 1139 PM CST THU FEB 26 2015

VFR conditions will prevail at all TAF sites next 24hrs. Clouds
around 4.5kft are still effecting BMI/DEC/CMI late tonight but are
slowly moving southeast and should clear BMI and DEC by 06z, and
CMI by 09z. Will keep a 2hr TEMPO group for DEC and CMI just
because it seems these clouds are just lingering and will not go
quickly. Then clear skies should prevail remainder of the TAF
period. Winds will be northwest overnight and then become light
and variable tomorrow.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY until 10 AM CST Friday FOR ILZ027>031-
036>038-040>051-053-055-057.

&&

$$

UPDATE...Auten
SHORT TERM...07
LONG TERM...Goetsch
AVIATION...Auten





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000
FXUS63 KLOT 270512
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1112 PM CST THU FEB 26 2015

.UPDATE...
827 PM CST

LAKE EFFECT SNOW IS STARTING TO WIND DOWN AS DRIER AIR MASS
ADVECTS INTO THE AREA ALLOWING FOR A WEAKENING OF THE BROKEN LES
BAND THAT HAD PERSISTED ALL DAY. AS PROGRESSIVELY DRIER AIR
CONTINUED TO FILTER IN TONIGHT AND EVENTUALLY ONSHORE COMPONENT TO
FLOW WEAKENS WOULD ANTICIPATE LES TO END IN PORTER COUNTY LATER
THIS EVENING OR JUST PAST MIDNIGHT. GIVEN EXPECTATIONS AND RECENT
RADAR TRENDS MAY SHORTEN THE DURATION OF THE LAKE EFFECT SNOW
WARNING IN THE NEXT HOUR OR TWO IF NOT CANCEL IT OUTRIGHT.

ELSEWHERE CLOUDINESS OVER SOUTHERN PORTIONS OF THE CWA IS LIKELY
TO SLOWLY DISSIPATE AND MOVE OUT LEAVING SKIES FAIRLY CLEAR ACROSS
THE AREA. CENTER OF THE HIGH PRESSURE IS STILL HUNDREDS OF MILE TO
OUR NORTHWEST BUT WITH FRESH SNOW PACK WOULD EXPECT GRADIENT TO BE
WEAK ENOUGH FOR WINDS TO FURTHER DECOUPLE OVERNIGHT...ESPECIALLY
WITH HIGH GROWING CLOSER IN TIME. SUSPECT THAT THE WIND CHILL
ADVISORY WILL BE HARD PRESSED TO VERIFY MOST AREAS WITH THE
TYPICALLY COLDER VALLEYS LIKELY SEEING WINDS GO CALM...LIKELY KRPJ
AND KFRD ALREADY HAVE OR WINDS TO STAY UP ENOUGH TO KEEP TEMPS
FROM TANKING. THE TOOTHPASTE IS OUT OF THE PROVERBIAL TUBE SO NOT
PLANNING ANY CHANGES TO THE WIND CHILL ADVISORY SINCE A FEW
LOCATIONS COULD TAG ADVISORY FOR AN HOUR OR TWO AND IT WILL BE
VERY COLD.

IZZI

&&

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MID 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE.

RATZER

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE CENTERED OVER THE MID-MISSOURI VALLEY EARLY THIS
MORNING WILL SPREAD SLOWLY EAST-SOUTHEAST ACROSS THE REGION
THROUGH TONIGHT. LIGHT NORTHWEST WINDS WILL BECOME WEST DURING THE
DAY AND SOUTHWEST TONIGHT...WITH SPEEDS GENERALLY LESS THAN 10 KT.
DRY ARCTIC AIR MASS WILL MAKE FOR MAINLY CLEAR SKIES THROUGH THE
PERIOD.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH FOR ALL ELEMENTS.

RATZER

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

SATURDAY...VFR THEN SNOW DEVELOPING SATURDAY NIGHT. IFR LIKELY.

SUNDAY...PERIODS OF ACCUMULATING SNOW ENDING BY LATE AFTERNOON.
IFR LIKELY.

MONDAY...VFR THEN CHANCE OF WINTRY MIX AND IFR MONDAY NIGHT.

TUESDAY...RAIN AND IFR LIKELY...POSSIBLY ENDING AS LIGHT SNOW
TUESDAY NIGHT. IFR

WEDNESDAY...MVFR POSSIBLE.

RC

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022
     UNTIL 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 270512
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1112 PM CST THU FEB 26 2015

.UPDATE...
827 PM CST

LAKE EFFECT SNOW IS STARTING TO WIND DOWN AS DRIER AIR MASS
ADVECTS INTO THE AREA ALLOWING FOR A WEAKENING OF THE BROKEN LES
BAND THAT HAD PERSISTED ALL DAY. AS PROGRESSIVELY DRIER AIR
CONTINUED TO FILTER IN TONIGHT AND EVENTUALLY ONSHORE COMPONENT TO
FLOW WEAKENS WOULD ANTICIPATE LES TO END IN PORTER COUNTY LATER
THIS EVENING OR JUST PAST MIDNIGHT. GIVEN EXPECTATIONS AND RECENT
RADAR TRENDS MAY SHORTEN THE DURATION OF THE LAKE EFFECT SNOW
WARNING IN THE NEXT HOUR OR TWO IF NOT CANCEL IT OUTRIGHT.

ELSEWHERE CLOUDINESS OVER SOUTHERN PORTIONS OF THE CWA IS LIKELY
TO SLOWLY DISSIPATE AND MOVE OUT LEAVING SKIES FAIRLY CLEAR ACROSS
THE AREA. CENTER OF THE HIGH PRESSURE IS STILL HUNDREDS OF MILE TO
OUR NORTHWEST BUT WITH FRESH SNOW PACK WOULD EXPECT GRADIENT TO BE
WEAK ENOUGH FOR WINDS TO FURTHER DECOUPLE OVERNIGHT...ESPECIALLY
WITH HIGH GROWING CLOSER IN TIME. SUSPECT THAT THE WIND CHILL
ADVISORY WILL BE HARD PRESSED TO VERIFY MOST AREAS WITH THE
TYPICALLY COLDER VALLEYS LIKELY SEEING WINDS GO CALM...LIKELY KRPJ
AND KFRD ALREADY HAVE OR WINDS TO STAY UP ENOUGH TO KEEP TEMPS
FROM TANKING. THE TOOTHPASTE IS OUT OF THE PROVERBIAL TUBE SO NOT
PLANNING ANY CHANGES TO THE WIND CHILL ADVISORY SINCE A FEW
LOCATIONS COULD TAG ADVISORY FOR AN HOUR OR TWO AND IT WILL BE
VERY COLD.

IZZI

&&

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MID 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE.

RATZER

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE CENTERED OVER THE MID-MISSOURI VALLEY EARLY THIS
MORNING WILL SPREAD SLOWLY EAST-SOUTHEAST ACROSS THE REGION
THROUGH TONIGHT. LIGHT NORTHWEST WINDS WILL BECOME WEST DURING THE
DAY AND SOUTHWEST TONIGHT...WITH SPEEDS GENERALLY LESS THAN 10 KT.
DRY ARCTIC AIR MASS WILL MAKE FOR MAINLY CLEAR SKIES THROUGH THE
PERIOD.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH FOR ALL ELEMENTS.

RATZER

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

SATURDAY...VFR THEN SNOW DEVELOPING SATURDAY NIGHT. IFR LIKELY.

SUNDAY...PERIODS OF ACCUMULATING SNOW ENDING BY LATE AFTERNOON.
IFR LIKELY.

MONDAY...VFR THEN CHANCE OF WINTRY MIX AND IFR MONDAY NIGHT.

TUESDAY...RAIN AND IFR LIKELY...POSSIBLY ENDING AS LIGHT SNOW
TUESDAY NIGHT. IFR

WEDNESDAY...MVFR POSSIBLE.

RC

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022
     UNTIL 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 270300
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
900 PM CST Thu Feb 26 2015

.UPDATE...
ISSUED AT 900 PM CST THU FEB 26 2015

Small area of clouds continues to slowly move south this evening.
Also, some isolated flurries are also still occurring under this
cloud cover. Expect this to continue, mainly in eastern areas of
the CWA. This will eventually clear up overnight. Current forecast
has a good handle on this and with temp trends the rest of the
night. No update planned at this time.

&&

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 548 PM CST THU FEB 26 2015

clouds and light snow showers continue at SPI/DEC/CMI. When the
snow occurs, cigs are MVFR and vis is below 5SM. PIA and BMI just
have clouds, but VFR levels. All sites will remain mostly cloudy
most of the evening and since clouds are not diurnal, they will
continue for several hours after sunset. So, think clearing will
occur close to midnight. With all the low level moisture around
tomorrow, believe scattered lower SC or CU will develop in the
morning. Winds will be north-northwest early and then become
northwest close to midnight. With ridging over the area tomorrow,
winds will be light.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

UPDATE...Auten
SHORT TERM...07
LONG TERM...Goetsch
AVIATION...Auten






000
FXUS63 KILX 270300
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
900 PM CST Thu Feb 26 2015

.UPDATE...
ISSUED AT 900 PM CST THU FEB 26 2015

Small area of clouds continues to slowly move south this evening.
Also, some isolated flurries are also still occurring under this
cloud cover. Expect this to continue, mainly in eastern areas of
the CWA. This will eventually clear up overnight. Current forecast
has a good handle on this and with temp trends the rest of the
night. No update planned at this time.

&&

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 548 PM CST THU FEB 26 2015

clouds and light snow showers continue at SPI/DEC/CMI. When the
snow occurs, cigs are MVFR and vis is below 5SM. PIA and BMI just
have clouds, but VFR levels. All sites will remain mostly cloudy
most of the evening and since clouds are not diurnal, they will
continue for several hours after sunset. So, think clearing will
occur close to midnight. With all the low level moisture around
tomorrow, believe scattered lower SC or CU will develop in the
morning. Winds will be north-northwest early and then become
northwest close to midnight. With ridging over the area tomorrow,
winds will be light.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

UPDATE...Auten
SHORT TERM...07
LONG TERM...Goetsch
AVIATION...Auten







000
FXUS63 KLOT 270227
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
827 PM CST THU FEB 26 2015

.UPDATE...
827 PM CST

LAKE EFFECT SNOW IS STARTING TO WIND DOWN AS DRIER AIR MASS
ADVECTS INTO THE AREA ALLOWING FOR A WEAKENING OF THE BROKEN LES
BAND THAT HAD PERSISTED ALL DAY. AS PROGRESSIVELY DRIER AIR
CONTINUED TO FILTER IN TONIGHT AND EVENTUALLY ONSHORE COMPONENT TO
FLOW WEAKENS WOULD ANTICIPATE LES TO END IN PORTER COUNTY LATER
THIS EVENING OR JUST PAST MIDNIGHT. GIVEN EXPECTATIONS AND RECENT
RADAR TRENDS MAY SHORTEN THE DURATION OF THE LAKE EFFECT SNOW
WARNING IN THE NEXT HOUR OR TWO IF NOT CANCEL IT OUTRIGHT.

ELSEWHERE CLOUDINESS OVER SOUTHERN PORTIONS OF THE CWA IS LIKELY
TO SLOWLY DISSIPATE AND MOVE OUT LEAVING SKIES FAIRLY CLEAR ACROSS
THE AREA. CENTER OF THE HIGH PRESSURE IS STILL HUNDREDS OF MILE TO
OUR NORTHWEST BUT WITH FRESH SNOW PACK WOULD EXPECT GRADIENT TO BE
WEAK ENOUGH FOR WINDS TO FURTHER DECOUPLE OVERNIGHT...ESPECIALLY
WITH HIGH GROWING CLOSER IN TIME. SUSPECT THAT THE WIND CHILL
ADVISORY WILL BE HARD PRESSED TO VERIFY MOST AREAS WITH THE
TYPICALLY COLDER VALLEYS LIKELY SEEING WINDS GO CALM...LIKELY KRPJ
AND KFRD ALREADY HAVE OR WINDS TO STAY UP ENOUGH TO KEEP TEMPS
FROM TANKING. THE TOOTHPASTE IS OUT OF THE PROVERBIAL TUBE SO NOT
PLANNING ANY CHANGES TO THE WIND CHILL ADVISORY SINCE A FEW
LOCATIONS COULD TAG ADVISORY FOR AN HOUR OR TWO AND IT WILL BE
VERY COLD.

IZZI

&&

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MID 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NONE.

RC/IZZI

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

HIGH PRESSURE SPREADING SOUTHEAST FROM THE NORTHERN PLAINS TO THE
MID MISSISSIPPI VALLEY WILL RESULT IN QUIET AVIATION CONDITIONS
THROUGH THE TAF PERIOD. NORTHWEST WINDS WILL DIMINISH TONIGHT AND
BECOME WESTERLY ON FRIDAY...WITH SPEEDS GENERALLY LESS THAN 10 KT.

RC

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

* HIGH IN ALL ELEMENTS.

RC/IZZI

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

SATURDAY...VFR THEN SNOW DEVELOPING SATURDAY NIGHT. IFR LIKELY.

SUNDAY...PERIODS OF ACCUMULATING SNOW ENDING BY LATE AFTERNOON.
IFR LIKELY.

MONDAY...VFR THEN CHANCE OF WINTRY MIX AND IFR MONDAY NIGHT.

TUESDAY...RAIN AND IFR LIKELY...POSSIBLY ENDING AS LIGHT SNOW
TUESDAY NIGHT. IFR

WEDNESDAY...MVFR POSSIBLE.

RC

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 270227
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
827 PM CST THU FEB 26 2015

.UPDATE...
827 PM CST

LAKE EFFECT SNOW IS STARTING TO WIND DOWN AS DRIER AIR MASS
ADVECTS INTO THE AREA ALLOWING FOR A WEAKENING OF THE BROKEN LES
BAND THAT HAD PERSISTED ALL DAY. AS PROGRESSIVELY DRIER AIR
CONTINUED TO FILTER IN TONIGHT AND EVENTUALLY ONSHORE COMPONENT TO
FLOW WEAKENS WOULD ANTICIPATE LES TO END IN PORTER COUNTY LATER
THIS EVENING OR JUST PAST MIDNIGHT. GIVEN EXPECTATIONS AND RECENT
RADAR TRENDS MAY SHORTEN THE DURATION OF THE LAKE EFFECT SNOW
WARNING IN THE NEXT HOUR OR TWO IF NOT CANCEL IT OUTRIGHT.

ELSEWHERE CLOUDINESS OVER SOUTHERN PORTIONS OF THE CWA IS LIKELY
TO SLOWLY DISSIPATE AND MOVE OUT LEAVING SKIES FAIRLY CLEAR ACROSS
THE AREA. CENTER OF THE HIGH PRESSURE IS STILL HUNDREDS OF MILE TO
OUR NORTHWEST BUT WITH FRESH SNOW PACK WOULD EXPECT GRADIENT TO BE
WEAK ENOUGH FOR WINDS TO FURTHER DECOUPLE OVERNIGHT...ESPECIALLY
WITH HIGH GROWING CLOSER IN TIME. SUSPECT THAT THE WIND CHILL
ADVISORY WILL BE HARD PRESSED TO VERIFY MOST AREAS WITH THE
TYPICALLY COLDER VALLEYS LIKELY SEEING WINDS GO CALM...LIKELY KRPJ
AND KFRD ALREADY HAVE OR WINDS TO STAY UP ENOUGH TO KEEP TEMPS
FROM TANKING. THE TOOTHPASTE IS OUT OF THE PROVERBIAL TUBE SO NOT
PLANNING ANY CHANGES TO THE WIND CHILL ADVISORY SINCE A FEW
LOCATIONS COULD TAG ADVISORY FOR AN HOUR OR TWO AND IT WILL BE
VERY COLD.

IZZI

&&

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MID 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NONE.

RC/IZZI

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

HIGH PRESSURE SPREADING SOUTHEAST FROM THE NORTHERN PLAINS TO THE
MID MISSISSIPPI VALLEY WILL RESULT IN QUIET AVIATION CONDITIONS
THROUGH THE TAF PERIOD. NORTHWEST WINDS WILL DIMINISH TONIGHT AND
BECOME WESTERLY ON FRIDAY...WITH SPEEDS GENERALLY LESS THAN 10 KT.

RC

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

* HIGH IN ALL ELEMENTS.

RC/IZZI

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

SATURDAY...VFR THEN SNOW DEVELOPING SATURDAY NIGHT. IFR LIKELY.

SUNDAY...PERIODS OF ACCUMULATING SNOW ENDING BY LATE AFTERNOON.
IFR LIKELY.

MONDAY...VFR THEN CHANCE OF WINTRY MIX AND IFR MONDAY NIGHT.

TUESDAY...RAIN AND IFR LIKELY...POSSIBLY ENDING AS LIGHT SNOW
TUESDAY NIGHT. IFR

WEDNESDAY...MVFR POSSIBLE.

RC

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262348
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
548 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 548 PM CST THU FEB 26 2015

clouds and light snow showers continue at SPI/DEC/CMI. When the
snow occurs, cigs are MVFR and vis is below 5SM. PIA and BMI just
have clouds, but VFR levels. All sites will remain mostly cloudy
most of the evening and since clouds are not diurnal, they will
continue for several hours after sunset. So, think clearing will
occur close to midnight. With all the low level moisture around
tomorrow, believe scattered lower SC or CU will develop in the
morning. Winds will be north-northwest early and then become
northwest close to midnight. With ridging over the area tomorrow,
winds will be light.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...Auten






000
FXUS63 KILX 262348
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
548 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 548 PM CST THU FEB 26 2015

clouds and light snow showers continue at SPI/DEC/CMI. When the
snow occurs, cigs are MVFR and vis is below 5SM. PIA and BMI just
have clouds, but VFR levels. All sites will remain mostly cloudy
most of the evening and since clouds are not diurnal, they will
continue for several hours after sunset. So, think clearing will
occur close to midnight. With all the low level moisture around
tomorrow, believe scattered lower SC or CU will develop in the
morning. Winds will be north-northwest early and then become
northwest close to midnight. With ridging over the area tomorrow,
winds will be light.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...Auten







000
FXUS63 KILX 262348
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
548 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.

&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
ISSUED AT 548 PM CST THU FEB 26 2015

clouds and light snow showers continue at SPI/DEC/CMI. When the
snow occurs, cigs are MVFR and vis is below 5SM. PIA and BMI just
have clouds, but VFR levels. All sites will remain mostly cloudy
most of the evening and since clouds are not diurnal, they will
continue for several hours after sunset. So, think clearing will
occur close to midnight. With all the low level moisture around
tomorrow, believe scattered lower SC or CU will develop in the
morning. Winds will be north-northwest early and then become
northwest close to midnight. With ridging over the area tomorrow,
winds will be light.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...Auten






000
FXUS63 KLOT 262329
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
529 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MID 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NONE.

RC

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

HIGH PRESSURE SPREADING SOUTHEAST FROM THE NORTHERN PLAINS TO THE
MID MISSISSIPPI VALLEY WILL RESULT IN QUIET AVIATION CONDITIONS
THROUGH THE TAF PERIOD. NORTHWEST WINDS WILL DIMINISH TONIGHT AND
BECOME WESTERLY ON FRIDAY...WITH SPEEDS GENERALLY LESS THAN 10 KT.

RC


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

* HIGH IN ALL ELEMENTS.

RC

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

SATURDAY...VFR THEN SNOW DEVELOPING SATURDAY NIGHT. IFR LIKELY.

SUNDAY...PERIODS OF ACCUMULATING SNOW ENDING BY LATE AFTERNOON.
IFR LIKELY.

MONDAY...VFR THEN CHANCE OF WINTRY MIX AND IFR MONDAY NIGHT.

TUESDAY...RAIN AND IFR LIKELY...POSSIBLY ENDING AS LIGHT SNOW
TUESDAY NIGHT. IFR

WEDNESDAY...MVFR POSSIBLE.

RC

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262205
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
405 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELLED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKLELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MIDS 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTH-NORTHWEST WINDS 8 TO 12 KT DIMINISHING TO BELOW 10 KT THIS
  EVENING.

RC

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

THE INTENSE LAKE EFFECT SNOW BAND IS PUSHING EAST OF GYY AND WILL CONTINUE
TO DO SO INTO THE EVENING. WINDS AT ORD AND MDW RANGE BETWEEN 330
AND 350 DEGREES AT ABOUT 8-12KT. PREVAILING SPEEDS WILL DIMINISH
TO BELOW 10 KT EARLY THIS EVENING...BY ABOUT 01Z AT ORD.

RC

FROM 18Z...

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

RC

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262205
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
405 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELLED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKLELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MIDS 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTH-NORTHWEST WINDS 8 TO 12 KT DIMINISHING TO BELOW 10 KT THIS
  EVENING.

RC

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

THE INTENSE LAKE EFFECT SNOW BAND IS PUSHING EAST OF GYY AND WILL CONTINUE
TO DO SO INTO THE EVENING. WINDS AT ORD AND MDW RANGE BETWEEN 330
AND 350 DEGREES AT ABOUT 8-12KT. PREVAILING SPEEDS WILL DIMINISH
TO BELOW 10 KT EARLY THIS EVENING...BY ABOUT 01Z AT ORD.

RC

FROM 18Z...

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

RC

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262205
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
405 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELLED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKLELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MIDS 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTH-NORTHWEST WINDS 8 TO 12 KT DIMINISHING TO BELOW 10 KT THIS
  EVENING.

RC

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

THE INTENSE LAKE EFFECT SNOW BAND IS PUSHING EAST OF GYY AND WILL CONTINUE
TO DO SO INTO THE EVENING. WINDS AT ORD AND MDW RANGE BETWEEN 330
AND 350 DEGREES AT ABOUT 8-12KT. PREVAILING SPEEDS WILL DIMINISH
TO BELOW 10 KT EARLY THIS EVENING...BY ABOUT 01Z AT ORD.

RC

FROM 18Z...

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

RC

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262100
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELLED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKLELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MIDS 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTHERLY WINDS 10 TO 14 KT BECOING NORTHWEST THIS EVENING.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

     WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

     LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262100
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELLED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKLELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MIDS 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTHERLY WINDS 10 TO 14 KT BECOING NORTHWEST THIS EVENING.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

     WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022...2
     AM FRIDAY TO 9 AM FRIDAY.

     LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262049
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
249 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.


&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...07






000
FXUS63 KILX 262049
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
249 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.


&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...07






000
FXUS63 KILX 262049
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
249 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.


&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...07






000
FXUS63 KILX 262049
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
249 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.


&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...07






000
FXUS63 KILX 262049
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
249 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.


&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...07







000
FXUS63 KILX 262049
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
249 PM CST Thu Feb 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 249 PM CST THU FEB 26 2015

Will issue a wind chill advisory for areas along and north of a
Jacksonville to Springfield to Decatur to Paris line overnight into
mid Fri morning for wind chills of 15-24F below zero with the
coldest wind chills in Knox and Stark counties around dawn Friday.
Wind chills reach near or below 15F below near Galesburg around
midnight, and se toward I-72 later tonight. Lows overnight to
range from 5-10F below zero from the IL river valley nw to zero to
5F above in southeast IL from I-70 se. Broken to overcast low
clouds still cover much of IL with some clearing far west central
and northern IL near WI border. Still getting scattered light snow
showers and areas of flurries over central IL (visibilities as low as
2-5 miles) due to lingering moisture off lake MI along with a short
wave dropping se into the area. HRRR may be a bit too progressive in
clearing low clouds from north to south during early and mid
evening. Low clouds to likely decrease over IL river valley early
this evening, but thinking it may take until overnight for
decreasing of low clouds in southeast IL since short wave still
affecting southern counties tonight. Also lingered chance of
flurries from I-55 east late this afternoon and early evening and
into mid evening in southeast IL. Strong 1042 mb arctic high
pressure near the MT/ND and southern Saskatchewan border and ridging
SSE into the Great Plains to settle se into IA/MO by Friday morning
bringing dry weather and bitter cold temperatures overnight into Fri
morning. North winds 10-17 mph and gusts 18-24 mph this afternoon
will veer nw and decrease to 5-10 mph overnight.


&&

.LONG TERM...(Friday through Thursday)
ISSUED AT 249 PM CST THU FEB 26 2015

Morning upper air and satellite imagery depicts trough over the
central plains with clipper shortwave moving over IL, producing
continued light snow in strong 850mb cold air advection. Wave
continuing to move east and will break up in afternoon.

Ridge of high pressure to build in overnight, again producing wind
chills. Ridge to move off to the east through Friday and into
Saturday. By Saturday afternoon, overrunning from the next system
begins to develop into plains. NAM model brings snow into western IL
and feel not unreasonable. Will therefore add slight chc pops Sat
afternoon, with main pcpn Sat night to Sunday.

Models similar in development of frontal zone from western plains
low into Ozarks, with significant lift over boundary Saturday night.
This will push snow formation into central IL Saturday night,
continuing into Sunday. Main lift is Saturday night as upper wave
moves across great lakes, with pcpn lingering into Sunday. Diminshed
the pcpn Sun night as high pressure builds in.

Upper flow changes Monday to Tuesday, with pcpn again developing
into Monday night to Tuesday as surface low center develops in
plains and moves northeast, west of cwa though. The result is that
with this feature, area stays in the warm section and so pcpn starts
as freezing rain and changes to rain. Still uncertainty though, as
the operational models are very different on the timing of the
system movement. made few changes due to these differences.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WIND CHILL ADVISORY from Midnight tonight to 10 AM CST Friday
FOR ILZ027>031-036>038-040>051-053-055-057.

&&

$$

SHORT TERM...07
LONG TERM...Goetsch
AVIATION...07






000
FXUS63 KLOT 262043
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
243 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELLED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKLELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MIDS 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

WILL BE ISSUED SOON.

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTHERLY WINDS 10 TO 14 KT BECOING NORTHWEST THIS EVENING.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262043
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
243 PM CST THU FEB 26 2015

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELLED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKLELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MIDS 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

WILL BE ISSUED SOON.

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTHERLY WINDS 10 TO 14 KT BECOING NORTHWEST THIS EVENING.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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 262008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
208 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* NORTHERLY WINDS 10 TO 14 KT BECOING NORTHWEST THIS EVENING.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

HIGH WITH ALL ELEMENTS.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 262004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* LINGERING LAKE EFFECT AND LOW VIS OVER THE NEXT COUPLE HOURS.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

MEDIUM TO HIGH ON ENDING OF SHOW SHOWERS AT MDW BY MID AFTERNOON.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 262004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* LINGERING LAKE EFFECT AND LOW VIS OVER THE NEXT COUPLE HOURS.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

MEDIUM TO HIGH ON ENDING OF SHOW SHOWERS AT MDW BY MID AFTERNOON.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 262004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* LINGERING LAKE EFFECT AND LOW VIS OVER THE NEXT COUPLE HOURS.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

MEDIUM TO HIGH ON ENDING OF SHOW SHOWERS AT MDW BY MID AFTERNOON.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 262004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* LINGERING LAKE EFFECT AND LOW VIS OVER THE NEXT COUPLE HOURS.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

MEDIUM TO HIGH ON ENDING OF SHOW SHOWERS AT MDW BY MID AFTERNOON.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 262004
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
204 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* LINGERING LAKE EFFECT AND LOW VIS OVER THE NEXT COUPLE HOURS.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB

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

MEDIUM TO HIGH ON ENDING OF SHOW SHOWERS AT MDW BY MID AFTERNOON.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
215 PM CST

THE FAR NORTHERN PORTIONS OF THE LAKE REMAINS ICE COVERED AS DO
THE SOUTHERN NEARSHORE WATERS. THERE...WAVES HAVE REMOVED FROM THE
FORECAST FOR THESE AREAS.

HIGH PRESSURE EXTENDS FROM THE NORTHERN PLAINS...WITH A CENTRAL
PRESSURE OF 30.8 INCHES...SOUTH THROUGH TEXAS AND EAST ACROSS THE
GREAT LAKES. THE CENTER OF THE HIGH WILL CONTINUE TO DROP TO THE
SOUTHEAST...TO THE UPPER MISSOURI VALLEY BY FRIDAY MORNING. WITH
RIDGE AXIS EXTENDING ACROSS LAKE MICHIGAN...A CONVERGENCE BAND HAS
SET UP WITH A PLUME OF LAKE EFFECT SNOW MOVING ACROSS THE SOUTHERN
PORTIONS OF THE LAKE. AS THE CENTER OF THE HIGH CONTINUES TO
SETTLE INTO THE OHIO VALLEY FRIDAY AND FRIDAY NIGHT...WINDS OVER
THE LAKE WILL BACK FROM NORTHERLY TO WESTERLY FRIDAY NIGHT AND
SATURDAY. AS THE HIGH MOVES OFF TO THE EAST...A WEAK COLD FRONT IS
EXPECTED TO CROSS THE UPPER MISSISSIPPI VALLEY SATURDAY
NIGHT...BACKING WINDS OVER THE LAKE TO SOUTHWESTERLY. THROUGH THIS
PERIOD...WINDS WILL BE ON A GENERAL WEAKENING TREND. THE WEAK COLD
FRONT IS EXPECTED TO SWEEP ACROSS THE LAKE SUNDAY EVENING WITH
ANOTHER ARCTIC HIGH QUICKLY FOLLOWING IN IT`S WAKE. THIS HIGH WILL
TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THE HIGH CROSSING
THE LAKE SUNDAY NIGHT AND MONDAY...LEADING TO A SHORT PERIOD OF
LIGHT AND VARIABLE WINDS. THE HIGH SHOULD THEN PUSH EAST OF THE
LAKE MONDAY AND MONDAY NIGHT AS LOW PRESSURE DEVELOPS OVER
KANSAS/NEBRASKA IN THE LEE OF THE ROCKIES...SETTING UP A PERIOD OF
SOUTHEAST WINDS AS AN ASSOCIATED WARM FRONT EXTENDS EAST OF THE
LOW...TO THE OHIO VALLEY. THE LOW IS EXPECTED TO DEEPEN TO 29.1
INCHES AS IT TRACKS NORTHEAST AND CROSSES THE MIDDLE OF LAKE
MICHIGAN TUESDAY EVENING.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261811
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1211 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* LINGERING LAKE EFFECT AND LOW VIS OVER THE NEXT COUPLE HOURS.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB


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

MEDIUM TO HIGH ON ENDING OF SHOW SHOWERS AT MDW BY MID AFTERNOON.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261811
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1211 PM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* LINGERING LAKE EFFECT AND LOW VIS OVER THE NEXT COUPLE HOURS.

KJB

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

THE FOCUS FOR LAKE EFFECT SNOW SHOWERS WILL GRADUALLY BEGIN TO SHIFT
EASTWARD INTO SOUTHERN COOK AND NORTHWESTERN INDIANA OVER THE NEXT
FEW HOURS. AREA SURFACE OBSERVATIONS INDICATE WINDS SHIFTING
NORTHERLY ACROSS LAKE AND NORTHERN COOK COUNTIES IN ILLINOIS. RADAR
TRENDS OVER THE PAST HOUR HAVE ALSO SHOWN A DECREASE IN INTENSITIES
ACROSS LAKE COUNTY ILLINOIS...WITH SEVERAL SITES NOW OUT OF THE SNOW
AREA. THESE SAME TRENDS SHOULD GRADUALLY SHIFT SOUTH AND EASTWARD
THROUGH THE AFTERNOON. A BETTER WELL DEVELOPED BAND OF LAKE EFFECT
SNOW SHOWERS WILL TRY TO MOVE OVER KMDW OVER THE NEXT HOUR OR
SO...AND THIS COULD RESULT IN ANOTHER BRIEF PERIOD OF LOW
VISIBILITIES...POSSIBLY DOWN TO A HALF MILE. CONDITIONS WILL
IMPROVE BY MID AFTERNOON AT KMDW...BUT AT KGYY PERIODS OF LAKE
EFFECT SNOW SHOWERS WILL CONTINUE THROUGH THE AFTERNOON...BEFORE
ABATING THIS EVENING.

AFTER THIS LAKE EFFECT FOCUS SHIFTS EAST OF THE TERMINALS A PERIOD
OF QUIET WEATHER IS EXPECTED FOR TONIGHT AND FRIDAY AS A SURFACE
RIDGE OF HIGH PRESSURE MOVES OVER CENTRAL ILLINOIS. WINDS ARE
EXPECTED TO BE RATHER LIGHT WITH A WESTERLY DIRECTION.

KJB


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

MEDIUM TO HIGH ON ENDING OF SHOW SHOWERS AT MDW BY MID AFTERNOON.

KJB

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261801
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1201 PM CST Thu Feb 26 2015

.UPDATE...
ISSUED AT 1045 AM CST THU FEB 26 2015

Updated the forecast at mid morning for ending of the winter
weather advisory over parts of central IL. Light snow will
diminish to flurries late this morning and afternoon with less
than a half inch of additional snow se of the IL river.
Temperatures currently near highs today ranging from near 15F nw
of IL river to mid 20s in southeast IL. North winds 10-20 mph will
cause temperatures to slowly fall this afternoon with some blowing
snow in open rural areas. Alberta clipper system will exit se of
IL today with light snow diminishing this afternoon. Some clearing
of low clouds nw of IL river by Knox, Stark and Schuyler counties.
But another short wave moving se toward IL this afternoon to
likely keep low clouds around rest of today over most of central
and southeast IL.

&&

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.

&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.

&&

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

&&

$$

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







000
FXUS63 KILX 261801
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1201 PM CST Thu Feb 26 2015

.UPDATE...
ISSUED AT 1045 AM CST THU FEB 26 2015

Updated the forecast at mid morning for ending of the winter
weather advisory over parts of central IL. Light snow will
diminish to flurries late this morning and afternoon with less
than a half inch of additional snow se of the IL river.
Temperatures currently near highs today ranging from near 15F nw
of IL river to mid 20s in southeast IL. North winds 10-20 mph will
cause temperatures to slowly fall this afternoon with some blowing
snow in open rural areas. Alberta clipper system will exit se of
IL today with light snow diminishing this afternoon. Some clearing
of low clouds nw of IL river by Knox, Stark and Schuyler counties.
But another short wave moving se toward IL this afternoon to
likely keep low clouds around rest of today over most of central
and southeast IL.

&&

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.

&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1159 AM CST THU FEB 26 2015

Light snow mainly se of the IL river at midday to gradually
diminish to scattered flurries during the afternoon. Carried vsbys
1.5-3 miles from I-55 se until mid afternoon and then mainly VFR
vsbys thereafter with flurries. MVFR ceilings to lift to low end
VFR ceilings during mid/late afternoon and then scatter out from
nw to se during mid/late evening. Another upper level short wave
to pass through IL later today and then clearing to come in behind
this feature by overnight. North winds 10-17 kts this afternoon to
veer NW and diminish to 4-8 kts by overnight and Friday morning as
1043 mb arctic high pressure over southern Sasketchewan settles
into IA/MO/IL by 18Z/noon Friday bringing fair wx and lighter winds.

&&

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

&&

$$

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






000
FXUS63 KILX 261648
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1048 AM CST Thu Feb 26 2015

.UPDATE...
ISSUED AT 1045 AM CST THU FEB 26 2015

Updated the forecast at mid morning for ending of the winter
weather advisory over parts of central IL. Light snow will
diminish to flurries late this morning and afternoon with less
than a half inch of additional snow se of the IL river.
Temperatures currently near highs today ranging from near 15F nw
of IL river to mid 20s in southeast IL. North winds 10-20 mph will
cause temperatures to slowly fall this afternoon with some blowing
snow in open rural areas. Alberta clipper system will exit se of
IL today with light snow diminishing this afternoon. Some clearing
of low clouds nw of IL river by Knox, Stark and Schuyler counties.
But another short wave moving se toward IL this afternoon to
likely keep low clouds around rest of today over most of central
and southeast IL.

&&

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.

&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 533 AM CST THU FEB 26 2015

Mostly MVFR conditions in -sn and low ceilings across central IL
TAF sites this morning. A few sites in IFR vsbys across the
heavier band from KSPI-KCMI. Gradually improving conditions
moving in from the NW as the system moves southward. By 18-19Z,
snowfall intensity to diminish substantially so expecting most
significant vsby restrictions to end while ceilings remain near
MVFR thresholds through the afternoon. Ceilings likely to scatter
out overnight. Winds NNE 12-14 kts until 00-03Z decreasing to 4-8
kts overnight.


&&

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

$$

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






000
FXUS63 KLOT 261636
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1036 AM CST THU FEB 26 2015

.UPDATE...
1023 AM CST

WITH PERSISTENT BANDS OF LAKE EFFECT SNOW SHOWERS MOVING INTO
NORTHEASTERN ILLINOIS AND NORTHWESTERN INDIANA...THE LAKE EFFECT
SNOW ADVISORY HAS BEEN UPGRADED TO A LAKE EFFECT SNOW WARNING. A
LAKE EFFECT SNOW WARNING IS ALSO BEING ISSUED FOR PORTER COUNTY IN
NORTHWESTERN INDIANA. SNOW ACCUMULATIONS OF 4 INCHES TO...
LOCALLY...AS HIGH AS 8 INCHES HAVE BEEN REPORTED OVER THE CHICAGO
METRO AREA. LATEST RADAR IMAGERY INDICATES PERSISTENT BANDS OF
LAKE EFFECT SNOW SHOWERS STREAMING INLAND FROM THE LAKE WITH
PARTICULARLY HEAVY BANDS EXTENDING FROM GARY...INDIANA THROUGH FAR
EASTERN COOK AND WILL COUNTIES. ANOTHER STRONG BAND IS JUST ALONG
THE LAKESHORE FROM NEAR WAUKEGAN TO NEAR O`HARE. THESE BANDS OF
LAKE EFFECT SNOW ARE SLOWLY PROGRESSING TO THE SOUTH AND
EAST...AND ANTICIPATE THAT MUCH OF THE ACTIVITY SHOULD END OVER
LAKE COUNTY...ILLINOIS BY EARLY THIS AFTERNOON. THE ENDING TIME OF
LAKE EFFECT SNOW FOR COOK COUNTY IS A LITTLE TRICKIER DUE TO THE
GEOPOLITICAL BOUNDARIES...BUT THE GENERAL TREND SHOULD BE FOR THE
SNOW TO END FROM NORTH TO SOUTH...WITH SNOW SHOWERS LIKELY
LINGERING OVER THE FAR SERN PORTIONS OF THE COUNTY INTO THIS
EVENING. THE LATEST SHORT RANGE...HIGH RES GUIDANCE SUGGESTS THAT
A LAKE PLUME SHOULD BE PROGRESSIVE THROUGH LAKE COUNTY INDIANA
THIS EVENING...BUT COULD POSSIBLY THEN LINGER OVER PORTER COUNTY
THROUGH MUCH OF THE NIGHT TONIGHT. EXPECT THAT LAKE
COUNTY...ILLINOIS AND NORTHERN COOK COUNTY COULD SEE AN ADDITIONAL
1 TO...LOCALLY...3 INCHES OF NEW SNOWFALL. LAKE COUNTY INDIANA
SHOULD SEE AN ADDITIONAL 2 TO...LOCALLY...4 INCHES. EXPECT THAT
PORTER COUNTY SHOULD RECEIVE 4 TO...LOCALLY...8 INCHES OF LAKE
EFFECT SNOW THIS EVENING AND OVERNIGHT TONIGHT.

KREIN

&&

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 15Z...

* IFR/LIFR SNOW SHOWERS THROUGH LATE MORNING AT ORD AND THROUGH
  EARLY TO MID AFTERNOON AT MDW. POSSIBLY BRIEF 1/2SM
  VISIBILITY...WITH HIGHER PROBABILITY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST DURING THE
  AFTERNOON. THE TRANSITION TO A NORTHWESTERLY WIND MAY NOT OCCUR
  UNTIL LATE AFTERNOON/EARLY EVENING.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.

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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.

//ORD AND MDW CONFIDENCE...UPDATED 15Z...

* HIGH IN SNOW SHOWERS THROUGH AT AROUND MIDDAY AT ORD AND THROUGH
  EARLY AFTERNOON AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY
  AT MDW...LOW AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH MIDDAY.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW WARNING...ILZ006 UNTIL 3 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...ILZ014 UNTIL 6 PM THURSDAY.

IN...LAKE EFFECT SNOW WARNING...INZ001 UNTIL 9 PM THURSDAY.

     LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261443
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
843 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 15Z...

* IFR/LIFR SNOW SHOWERS THROUGH LATE MORNING AT ORD AND THROUGH
  EARLY TO MID AFTERNOON AT MDW. POSSIBLY BRIEF 1/2SM
  VISIBILITY...WITH HIGHER PROBABILITY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST DURING THE
  AFTERNOON. THE TRANSITION TO A NORTHWESTERLY WIND MAY NOT OCCUR
  UNTIL LATE AFTERNOON/EARLY EVENING.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.

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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.

//ORD AND MDW CONFIDENCE...UPDATED 15Z...

* HIGH IN SNOW SHOWERS THROUGH AT AROUND MIDDAY AT ORD AND THROUGH
  EARLY AFTERNOON AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY
  AT MDW...LOW AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH MIDDAY.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261443
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
843 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 15Z...

* IFR/LIFR SNOW SHOWERS THROUGH LATE MORNING AT ORD AND THROUGH
  EARLY TO MID AFTERNOON AT MDW. POSSIBLY BRIEF 1/2SM
  VISIBILITY...WITH HIGHER PROBABILITY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST DURING THE
  AFTERNOON. THE TRANSITION TO A NORTHWESTERLY WIND MAY NOT OCCUR
  UNTIL LATE AFTERNOON/EARLY EVENING.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.

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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.

//ORD AND MDW CONFIDENCE...UPDATED 15Z...

* HIGH IN SNOW SHOWERS THROUGH AT AROUND MIDDAY AT ORD AND THROUGH
  EARLY AFTERNOON AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY
  AT MDW...LOW AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH MIDDAY.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261443
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
843 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 15Z...

* IFR/LIFR SNOW SHOWERS THROUGH LATE MORNING AT ORD AND THROUGH
  EARLY TO MID AFTERNOON AT MDW. POSSIBLY BRIEF 1/2SM
  VISIBILITY...WITH HIGHER PROBABILITY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST DURING THE
  AFTERNOON. THE TRANSITION TO A NORTHWESTERLY WIND MAY NOT OCCUR
  UNTIL LATE AFTERNOON/EARLY EVENING.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.

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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.

//ORD AND MDW CONFIDENCE...UPDATED 15Z...

* HIGH IN SNOW SHOWERS THROUGH AT AROUND MIDDAY AT ORD AND THROUGH
  EARLY AFTERNOON AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY
  AT MDW...LOW AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH MIDDAY.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261220
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
620 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* IFR/LIFR SNOW SHOWERS THROUGH MID TO LATE MORNING. POSSIBLY
  BRIEF 1/4SM TO 1/2SM VISIBILITY...WITH HIGHER PROBABILITY AT
  MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20
  KT THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST LATE THIS
  MORNING OR EARLY THIS AFTERNOON.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.


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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.


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

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 16Z AT ORD AND THROUGH THE
  MORNING AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY AT
  MDW...LOW-MEDIUM AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH 15Z.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.


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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261220
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
620 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* IFR/LIFR SNOW SHOWERS THROUGH MID TO LATE MORNING. POSSIBLY
  BRIEF 1/4SM TO 1/2SM VISIBILITY...WITH HIGHER PROBABILITY AT
  MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20
  KT THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST LATE THIS
  MORNING OR EARLY THIS AFTERNOON.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.


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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.


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

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 16Z AT ORD AND THROUGH THE
  MORNING AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY AT
  MDW...LOW-MEDIUM AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH 15Z.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.


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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261220
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
620 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* IFR/LIFR SNOW SHOWERS THROUGH MID TO LATE MORNING. POSSIBLY
  BRIEF 1/4SM TO 1/2SM VISIBILITY...WITH HIGHER PROBABILITY AT
  MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20
  KT THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST LATE THIS
  MORNING OR EARLY THIS AFTERNOON.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.


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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.


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

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 16Z AT ORD AND THROUGH THE
  MORNING AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY AT
  MDW...LOW-MEDIUM AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH 15Z.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.


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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261220
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
620 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

FOR TONIGHT...A CLEARING SKY AND CONTINUED COLD ADVECTION WILL SET
THE STAGE FOR -15 TO -25 WIND CHILLS DEVELOPING OVERNIGHT INTO
FRIDAY MORNING. AT THIS TIME HAVE NOT ISSUED AN ADVISORY BUT IT
APPEARS DAY SHIFT MAY VERY WELL NEED ONE FOR AT LEAST NORTH
CENTRAL ILLINOIS. AS FOR ACTUAL LOW TEMPERATURES...BELOW ZERO ARE
EXPECTED AREAWIDE OUTSIDE OF DOWNTOWN CHICAGO...WITH NEGATIVE
DOUBLE DIGITS IN THE FAVORED SPOTS BECOMING MORE PROBABLE.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY AFTERNOON THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS THROUGH THE LATTER HALF OF THIS WEEK...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

TODAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* IFR/LIFR SNOW SHOWERS THROUGH MID TO LATE MORNING. POSSIBLY
  BRIEF 1/4SM TO 1/2SM VISIBILITY...WITH HIGHER PROBABILITY AT
  MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20
  KT THROUGH THE MORNING. WINDS TURNING NORTH-NORTHWEST LATE THIS
  MORNING OR EARLY THIS AFTERNOON.

* MVFR CIGS IN LAKE EFFECT SNOW WITH OCCASIONAL IFR VERTICAL
  VISIBILITY IN HEAVIER SNOW SHOWERS.


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

LAKE EFFECT SNOW SHOWERS WILL CONTINUE THIS MORNING INTO NORTHEAST
ILLINOIS AND NORTHWEST INDIANA. THE CONDITIONS THAT WERE OBSERVED
OVERNIGHT BASICALLY WILL PERSIST AT ORD AND MDW THROUGH 15Z TO 16Z
OR SO...WITH TEMPORARY LIFR VISIBILITY IN THE MODERATE TO BRIEFLY
HEAVY SNOW BANDS. BECAUSE THESE BANDS ARE SMALL IN
WIDTH...TEMPORARY CONDITIONS ARE THE NATURE AND CONTINUE TO GO
THAT ROUTE WITH THE TAF. THE LOW-LEVEL WIND FLOW WILL ORIENT MORE
DUE NORTH BY LATER MORNING AND EARLY AFTERNOON...STEERING THE BULK
OF THE LAKE EFFECT ACTIVITY INTO NORTHWEST INDIANA. HAVE THE
LOWEST VISIBILITY AT GYY MORE SO DURING THAT TIME...ALTHOUGH THEY
COULD HAVE THAT LOW OF VISIBILITY EVEN EARLIER THIS MORNING.

THE EXACT TIMING OF WHEN THE WINDS SHIFT MORE NORTH-NORTHWEST AT
ORD IS CHALLENGING...AS THE LAKE EFFECT SNOW BANDS ARE PARTLY
DICTATING THAT. SO CONFIDENCE ON THAT IS LOW.

BY AFTERNOON...DRIER AIR WILL WORK INTO ORD AND MDW ENDING THE
LAKE EFFECT SNOW THREAT. WINDS WILL EASE IN SPEED AND SLOWLY BACK
TONIGHT.


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

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 16Z AT ORD AND THROUGH THE
  MORNING AT MDW. MEDIUM-HIGH IN TEMPORARY LIFR VISIBILITY AT
  MDW...LOW-MEDIUM AT ORD.

* HIGH ON WINDS BEING MORE NORTHEAST THAN DUE NORTH THROUGH 15Z.
  LOW ON TIMING OF WIND SHIFT TO NORTH-NORTHWEST.

* MEDIUM-HIGH ON CIGS.


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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...VFR THEN SNOW WITH IFR PROBABLE SATURDAY NIGHT. SOUTH
           WINDS.
SUNDAY...SNOW WITH IFR POSSIBLE. SOUTHWEST WINDS.
MONDAY...VFR THEN LIGHT SNOW WITH IFR POSSIBLE MONDAY NIGHT. NORTH
         WINDS.
TUESDAY...WINTRY MIX LIKELY WITH IFR. SOUTHWEST WINDS.
WEDNESDAY...SLIGHT CHANCE OF SNOW AND IFR. NORTHWEST WINDS.

MTF

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 261148
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
548 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.

&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 533 AM CST THU FEB 26 2015

Mostly MVFR conditions in -sn and low ceilings across central IL
TAF sites this morning. A few sites in IFR vsbys across the
heavier band from KSPI-KCMI. Gradually improving conditions
moving in from the NW as the system moves southward. By 18-19Z,
snowfall intensity to diminish substantially so expecting most
significant vsby restrictions to end while ceilings remain near
MVFR thresholds through the afternoon. Ceilings likely to scatter
out overnight. Winds NNE 12-14 kts until 00-03Z decreasing to 4-8
kts overnight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Onton






000
FXUS63 KILX 261148
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
548 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.

&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 533 AM CST THU FEB 26 2015

Mostly MVFR conditions in -sn and low ceilings across central IL
TAF sites this morning. A few sites in IFR vsbys across the
heavier band from KSPI-KCMI. Gradually improving conditions
moving in from the NW as the system moves southward. By 18-19Z,
snowfall intensity to diminish substantially so expecting most
significant vsby restrictions to end while ceilings remain near
MVFR thresholds through the afternoon. Ceilings likely to scatter
out overnight. Winds NNE 12-14 kts until 00-03Z decreasing to 4-8
kts overnight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Onton







000
FXUS63 KILX 261148
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
548 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.

&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 533 AM CST THU FEB 26 2015

Mostly MVFR conditions in -sn and low ceilings across central IL
TAF sites this morning. A few sites in IFR vsbys across the
heavier band from KSPI-KCMI. Gradually improving conditions
moving in from the NW as the system moves southward. By 18-19Z,
snowfall intensity to diminish substantially so expecting most
significant vsby restrictions to end while ceilings remain near
MVFR thresholds through the afternoon. Ceilings likely to scatter
out overnight. Winds NNE 12-14 kts until 00-03Z decreasing to 4-8
kts overnight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Onton







000
FXUS63 KILX 261148
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
548 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.

&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 533 AM CST THU FEB 26 2015

Mostly MVFR conditions in -sn and low ceilings across central IL
TAF sites this morning. A few sites in IFR vsbys across the
heavier band from KSPI-KCMI. Gradually improving conditions
moving in from the NW as the system moves southward. By 18-19Z,
snowfall intensity to diminish substantially so expecting most
significant vsby restrictions to end while ceilings remain near
MVFR thresholds through the afternoon. Ceilings likely to scatter
out overnight. Winds NNE 12-14 kts until 00-03Z decreasing to 4-8
kts overnight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Onton






000
FXUS63 KLOT 260953
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
353 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.

//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 260953
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
353 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.

//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
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000
FXUS63 KLOT 260953
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
353 AM CST THU FEB 26 2015

.SHORT TERM...
345 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS ARE LAKE EFFECT SNOW SHOWERS AND THEIR
IMPACTS.

THE UPPER WAVE THAT HAS BROUGHT SNOW TO THE ENTIRE AREA YESTERDAY
AFTERNOON AND NIGHT CONTINUES LIGHT SNOW EARLY THIS MORNING.
THIS WILL VERY GRADUALLY DEPART SOUTHEAST THROUGH THE MORNING WITH
DIMINISHING DEEP LAYER MOISTURE. LITTLE ADDITIONAL ACCUMULATION
IS EXPECTED WITH THIS BUT WILL LIKELY SLOW THE MORNING COMMUTE
AREAWIDE. SOME LINGERING LIGHT SNOW MAY CONTINUE ALONG AND SOUTH
OF HIGHWAY 24 AS LATE AS EARLY THIS AFTERNOON.

WHILE THE SYNOPTIC SNOW IS TAPERING...SEVERAL LAKE EFFECT SNOW BANDS
EXTEND FROM THE LAKE INTO NORTHEAST IL AND FAR SOUTHEAST WI AND HAVE
BRIEFLY BEEN HEAVY IN INTENSITY PER RADAR AND OBSERVATIONS/REPORTS.
THE CONVERGENCE IS WELL-DEFINED ON OBSERVATIONAL STREAMLINE ANALYSIS
AND DO NOT SEE MUCH CHANGE IN THIS OCCURRING THROUGH MID MORNING
BEFORE A SLOW PIVOT INTO NORTHWEST INDIANA. COLDER AIR CONTINUES
TO ADVECT INTO THE REGION ON NORTH-NORTHEAST WINDS STEEPENING
LAKE-INDUCED LAPSE RATES AND ALLOWING FOR AT LEAST SUSTAINED CLOUD
DEPTHS. OFFSETTING THIS THOUGH IS MUCH DRIER LOW- LEVEL AIR
ADVECTING INTO THE REGION...WITH DEW POINTS OF -5 TO -15 ACROSS
LOWER MICHIGAN. THE THOUGHT IS THAT THIS DRY AIR MAY COME MORE
INTO PLAY LATER TODAY AND TONIGHT...BUT FOR THE MEANTIME LAKE
EFFECT SNOW SHOWERS SHOULD CONTINUE ACROSS CHICAGO AND FAR
NORTHEAST ILLINOIS AND NORTHERN PARTS OF LAKE COUNTY INDIANA. SNOW
RATIOS FROM A COUPLE SOURCES WITH MOSTLY LAKE EFFECT SNOW HAVE
INDICATED 20:1 TYPE RATIOS WHICH IS CONCURRENT WITH THERMAL AND
MOISTURE PROFILES ON LATEST AMDAR DATA...WHICH SHOW A DEEP
ISOTHERMAL LAYER AROUND 7000 FT IN THE IDEAL SNOW GROWTH AREA.
HAVE THESE HIGHER RATIOS IN THE FORECAST WITH A SLIGHTLY BOOSTED
QPF FROM THE LOCAL 8KM ARW. ADDITIONAL AMOUNTS AFTER SUNRISE OF
ONE TO THREE INCHES ARE EXPECTED. THIS ON TOP OF THE ALREADY
FALLEN SNOW ALONG WITH THE TIMING FURTHER SUPPORTS THE ADVISORY IN
EFFECT.

AS FOR PORTER COUNTY INDIANA...THIS BECOMES MORE CHALLENGING AS HIGH
RESOLUTION MODELS REALLY AGREE ON MORE OF A ONE SNOW BAND EVOLUTION
BY LATER TODAY INTO EVENING FOR NORTHWEST INDIANA...WHICH COULD IN
THEORY MEAN A QUICK FEW INCHES OF SNOW INCLUDING INTO PORTER
COUNTY. THE MUCH DRIER SYNOPTIC AIR MASS WILL ONLY FURTHER DRY
AND DEEPEN INTO THIS EVENING...SO IT GETS A BIT TRICKY. GIVEN THE
LATER TODAY INTO EVENING TIMING...HAVE OPTED TO ALLOW DAY SHIFT
TO ASSESS ADVISORY BUT WILL HIGHLIGHT IN AN SPS FOR NOW.

FRESH SNOW COVER AND MORNING CLOUDS ALONG WITH NORTHERLY WINDS
WILL BASICALLY STIFLE ANY TEMPERATURE RISE TODAY. READINGS IN THE
TEENS WILL BE CLOSE TO A RECORD LOW MAXIMUM IN ROCKFORD...BUT AT
THIS POINT THE FORECAST IS SLIGHTLY WARMER.

MTF

&&

.LONG TERM...
331 AM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...
345 AM CST

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.

//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 260935
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

UPDATED OVERNIGHT SHORT TERM DISCUSSION FORTHCOMING. SEE MESOSCALE
DISCUSSION ABOVE FOR LAKE EFFECT SNOW DETAILS.

DISCUSSION FROM 300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL
AMOUNTS THRU THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS
OVERNIGHT THRU THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...
331 AM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.

//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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

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





000
FXUS63 KLOT 260935
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

UPDATED OVERNIGHT SHORT TERM DISCUSSION FORTHCOMING. SEE MESOSCALE
DISCUSSION ABOVE FOR LAKE EFFECT SNOW DETAILS.

DISCUSSION FROM 300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL
AMOUNTS THRU THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS
OVERNIGHT THRU THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...
331 AM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.

//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 260935
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

UPDATED OVERNIGHT SHORT TERM DISCUSSION FORTHCOMING. SEE MESOSCALE
DISCUSSION ABOVE FOR LAKE EFFECT SNOW DETAILS.

DISCUSSION FROM 300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL
AMOUNTS THRU THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS
OVERNIGHT THRU THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...
331 AM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.

//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 260935
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
335 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

UPDATED OVERNIGHT SHORT TERM DISCUSSION FORTHCOMING. SEE MESOSCALE
DISCUSSION ABOVE FOR LAKE EFFECT SNOW DETAILS.

DISCUSSION FROM 300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL
AMOUNTS THRU THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS
OVERNIGHT THRU THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...
331 AM CST

FRIDAY NIGHT THROUGH WEDNESDAY...

AFTER A BITTERLY COLD START TO FRIDAY...LAKE EFFECT SNOW SHOWERS
WILL HAVE NOW SHIFTED EAST OF THE AREA AS THE SLOW MOVING UPPER
TROUGH AXIS BEGINS TO PUSH EASTWARD AS WELL...AND STRONG HIGH
PRESSURE SETTLES INTO THE REGION. 850 TEMPS WARM ONLY TO THE MID
TEENS BELOW ZERO RESULTING IN ANOTHER VERY COLD THOUGH SUNNY DAY.
HIGHS ONLY IN THE TEENS. WITH THE HIGH IN THE REGION FRIDAY
NIGHT...EXPECT CLEAR SKIES BRINGING ANOTHER BITTERLY COLD NIGHT WITH
LOWS BELOW ZERO IN MANY LOCATIONS. WITH THE HIGH NOT ENTIRELY
OVERHEAD...SOME WIND COMPONENT WILL BRING WIND CHILLS DOWN IN THE
-5 TO -20 RANGE.

THE SURFACE HIGH PUSHES OFF TO THE EAST ON SATURDAY AND WE GET INTO
RETURN FLOW ON THE BACKSIDE. 850 FLOW BECOMES DUE SOUTHERLY WHICH
WILL ALLOW THE LOW LEVEL AIR MASS TO MODERATE AND MOISTEN BUT ONLY
A LITTLE AS WE MAINTAIN AN ESE SURFACE FLOW WHICH SHOULD BE COOLER
AND DRIER. MEANWHILE ALOFT THE FLOW IS TURNING SOUTHWESTERLY OUT
AHEAD OF A DEEP UPPER LOW THAT WILL CLOSE OFF IN SOUTHERN CALIFORNIA
ALONG WITH A NORTHERN STREAM LOW/TROUGH SPREADING EAST THROUGH THE
CANADIAN PRAIRIES AND UPPER MIDWEST. HIGHS WARM INTO THE UPPER TEENS
NORTH TO LOWER 20S SOUTH WITH INCREASING CLOUDS ESPECIALLY IN THE
AFTERNOON.

LATER SATURDAY AFTERNOON AND EVENING...MORE SIGNIFICANT WARM/MOIST
ADVECTION THAT WILL BE ONGOING ACROSS THE PLAINS WILL PUSH NORTHWARD
TOWARD OUR AREA. THE STRONGER MOISTURE TRANSPORT WILL BE DIRECTED
SOUTH AND EAST OF OUR AREA BUT WILL GRAZE OUR SOUTHERN AREAS AS WELL
WITH MORE MODEST TRANSPORT FARTHER NORTH. STILL FAIRLY DEEP MOISTURE
AS SOUNDINGS ARE SATURATED THROUGH THE ENTIRE COLUMN. SEVERAL SUBTLE
SHORTWAVES WILL RIDE NORTHWESTWARD OUT AHEAD OF THE CALIFORNIA
LOW...THE FIRST ACCOMPANYING THE WARM/MOIST ADVECTION SATURDAY NIGHT
TO PRODUCE A ROUND OF SNOW THAT SHOULD INCREASE AREA WIDE FROM NORTH
TO SOUTH THROUGH THE EVENING AND ESPECIALLY OVERNIGHT.

THE BROAD WARM ADVECTION CONTINUES ON SUNDAY WITH A STRONG UPPER JET
INTENSIFYING RIGHT OVERHEAD. EXPECT CONTINUED SNOWFALL THOUGH THE
DAY WITH MORE MODERATE AMOUNTS FROM CHICAGO SOUTHWARD. HIGHEST
AMOUNTS AT THIS POINT LOOK TO BE SOUTH AND EAST INTO NW INDIANA AND
INTO CENTRAL ILLINOIS. MEANWHILE A NORTHERN STREAM TROUGH WILL BE
MOVING THROUGH THE NORTHERN PLAINS AND UPPER MIDWEST. THIS WILL
CROSS WISCONSIN SUNDAY EVENING...WITH MODEST HIGH PRESSURE BUILDING
IN QUICKLY BEHIND IT FOR QUIET CONDITIONS ON MONDAY.

BUT THE HIGH WILL BE SHORT LIVED AS THE UPPER LOW IN THE SOUTHWEST
BEGINS TO SLOWLY EJECT EASTWARD. MORE SIGNIFICANT WARM/MOIST
ADVECTION DUE TO 850 WINDS IN EXCESS OF 30KT AND PRECIPITABLE WATER
VALUES IN EXCESS OF 0.75 INCHES WILL BE ACCOMPANIED BY SOME BETTER
DYNAMICS AS THE UPPER JET STRENGTHENS TO OUR NORTH. AS MENTIONED IN
PREVIOUS DISCUSSIONS...THIS SYSTEM LOOKS TO HAVE SOME SIGNIFICANTLY
WARMER AIR WITH IT. THIS CREATES A POTENTIALLY MESSY SITUATION
DURING THE TRANSITION PERIOD AS 850 TEMPS...WHICH START TUESDAY
NIGHT AROUND -2C TO -8C FROM SOUTH TO NORTH RAPIDLY INCREASE TO +7C
SOUTH OR HIGHER TO AROUND +1 TO +3C ALONG THE WISCONSIN BORDER.
MEANWHILE SURFACE FLOW HANGS ONTO A E/SE DIRECTION THUS POTENTIALLY
DELAYING SURFACE WARMING. HAVE TRENDED WEATHER WORDING TOWARD THESE
WARMER SOLUTIONS WITH GFS/EC IN BETTER AGREEMENT IN SHOWING SNOW
TRANSITIONING TO A MIX AND THEN ALL RAIN EXCEPT IN THE FAR NORTH.
BUT CONFIDENCE IS STILL LOW AT THIS POINT GIVEN THE DYNAMICAL NATURE
OF THE SYSTEM. THE SURFACE LOW WITH THIS SYSTEM MOVES EAST TUESDAY
NIGHT ALLOWING COOLER AIR TO FILTER IN BEHIND IT. THINGS STAY ACTIVE
BEYOND THIS TIME AS WE WAIT FOR THE TROUGH IN THE WEST TO FINALLY
CROSS THE AREA.

KMD

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.

//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ006-ILZ014 UNTIL NOON THURSDAY.

IN...LAKE EFFECT SNOW ADVISORY...INZ001 UNTIL 9 PM THURSDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     THURSDAY.

&&

$$

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 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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








000
FXUS63 KILX 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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








000
FXUS63 KILX 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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








000
FXUS63 KILX 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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








000
FXUS63 KILX 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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







000
FXUS63 KILX 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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







000
FXUS63 KILX 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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







000
FXUS63 KILX 260925
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)
ISSUED AT 325 AM CST THU FEB 26 2015

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


&&

.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CST THU FEB 26 2015

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for
Wednesday.


&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST this morning FOR
ILZ027>031-036>038-040-041-047-049-050.

&&

$$

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







000
FXUS63 KLOT 260907
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
307 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ014 UNTIL NOON THURSDAY.

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 260907
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
307 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ014 UNTIL NOON THURSDAY.

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 260907
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
307 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ014 UNTIL NOON THURSDAY.

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 260907
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
307 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 14Z-16Z AT ORD AND THROUGH
  THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
259 AM CST

THE LAKE WILL GENERALLY REMAIN BETWEEN LOW PRESSURE SYSTEMS
THROUGH THE WEEKEND. PRESENTLY LAKE EFFECT SNOW SHOWERS...SOME OF
THEM HEAVY...WILL CONTINUE ACROSS THE SOUTHERN HALF OF THE LAKE
THROUGH TONIGHT. ASSOCIATED WITH THESE BANDS ARE SOME GUSTY WINDS
TO 30 KT. HAVE ISSUED A SMALL CRAFT ADVISORY FOR THE ILLINOIS AND
PART OF THE INDIANA NEARSHORE FOR THIS REASON. ICE COVERAGE OF
COURSE WILL DAMPEN MOST IF NOT ALL WAVE ACTION THERE.

HIGH PRESSURE WILL SLIDE JUST SOUTH OF LAKE MICHIGAN FRIDAY NIGHT
AND SLOWLY EXPAND UP TO THE EASTERN LAKES ON SATURDAY. A LOW
PRESSURE TROUGH BETWEEN NORTHERN AND SOUTHERN STREAM LOW PRESSURE
SYSTEMS WILL INCH ITS WAY OVER THE LAKE LATE SATURDAY NIGHT INTO
SUNDAY. A COLD FRONT WILL BASICALLY DEVELOP WITH THIS AND MOVE
OVER THE LAKE LATER SUNDAY SHIFTING WINDS BACK TO THE NORTHWEST.
LOW PRESSURE IS EXPECTED TO MOVE NORTHEAST NEAR OR OVER THE GREAT
LAKES REGION SOMETIME TUESDAY OR TUESDAY NIGHT WHICH COULD BRING
GUSTIER WINDS...BUT TOO MUCH UNCERTAINTY WITH THIS PATTERN IN THE
EXTENDED FORECAST TO HAVE MUCH CONFIDENCE.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...LAKE EFFECT SNOW ADVISORY...ILZ014 UNTIL NOON THURSDAY.

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 260607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1207 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 13Z-15Z AT ORD AND THROUGH
  MUCH OF THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1207 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 13Z-15Z AT ORD AND THROUGH
  MUCH OF THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1207 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 13Z-15Z AT ORD AND THROUGH
  MUCH OF THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1207 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 13Z-15Z AT ORD AND THROUGH
  MUCH OF THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1207 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 13Z-15Z AT ORD AND THROUGH
  MUCH OF THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260607
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1207 AM CST THU FEB 26 2015

.MESOSCALE DISCUSSION...
1200 AM CST

SEMI-ORGANIZED MODERATE TO AT TIMES HEAVY LAKE EFFECT SNOW
SHOWERS HAVE BEEN STREAMING INTO NORTHEAST ILLINOIS OVER THE PAST
COUPLE HOURS. THIS HAS BECOME THE MORE IMPACTING PHENOMENON AS THE
SYNOPTIC SNOW FROM THE UPPER LEVEL SHORT WAVE EASE SOUTHEAST.

REPORTS AT MIDNIGHT INDICATE SNOW OF AROUND AN INCH TO INCH AND A
HALF HAVE BEEN OBSERVED IN THE PAST TWO-THREE HOURS IN COOK
COUNTY. RADAR ECHOES OF 25-30 DBZ HAVE CORRELATED WITH VISIBILITY
OF ONE HALF TO AT TIMES ONE QUARTER MILE WITH SOME OF THIS LAKE
EFFECT SNOW ACTIVITY...INDICATING AT LEAST TEMPORARY HEAVY
RATES UNDER THESE SHOWERS. ON THE LARGE SCALE...LOW-LEVEL DRY AIR
IS ADVANCING SOUTHWARD...BUT NOT SURE IF THIS WILL HAVE MUCH
IMPACT ON THE LAKE EFFECT SNOW SHOWERS AS LAKE-INDUCED EQUILIBRIUM
LEVELS ARE ACTUALLY FORECAST TO IMPROVE WITH THE COOLING AIR MASS.
IN ADDITION...AMDAR DATA INDICATES ISOTHERMAL PROFILES OF AROUND
8000 FT THICK IN THE IDEAL SNOW GROWTH AREA WHERE THIS LAKE EFFECT
CONVERGENCE IS STREAMING INTO NORTHEAST IL. WITH MESOSCALE
CONVERGENCE LIKELY TO HOLD INTO NORTHEAST ILLINOIS THROUGH MID-
MORNING OR SO...MAY END UP NEEDING A LAKE EFFECT SNOW ADVISORY FOR
COOK COUNTY SIMPLY FOR THE AT TIMES HEAVIER RATES INTO THE MORNING
COMMUTE AND ADDITIONAL ACCUMULATIONS THAT COULD NEAR THREE INCHES
IF A BAND OR BANDS HOLD IN ANY ONE PLACE FOR A COUPLE/FEW HOURS OR
SO. WILL CLOSELY MONITOR OBSERVATIONAL TRENDS AND SNOWFALL REPORTS
AND ESTIMATES FROM ANY LATE NIGHT REPORTS. WILL ALSO NEED TO
ASSESS IF SUCH AN ADVISORY WILL BE NEEDED TODAY FOR LAKE AND
PORTER COUNTIES IN INDIANA.

MTF

&&

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* IFR/LIFR SNOW SHOWERS THROUGH AT LEAST MID TO LATE MORNING.
  POSSIBLY BRIEF 1/4SM VISIBILITY NAMELY AT MDW.

* NORTH-NORTHEAST WINDS WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT
  THROUGH THE MORNING.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW SHOWERS.


//DISCUSSION...UPDATED 06Z...

THE UPPER LEVEL WAVE THAT HAS BROUGHT WIDESPREAD SNOW TO NORTHERN
ILLINOIS AND NORTHWEST INDIANA WILL GRADUALLY SHIFT EASTWARD
THROUGH THE MORNING HOURS. WHILE THAT WILL QUICKLY BECOME LESS OF
A FACTOR...THE SETUP FOR LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO
IMPROVE. THERMAL PROFILES FROM AMDAR DATA INDICATE AROUND 8000 FT
IN THE IDEAL SNOW GENERATION AREA WITHIN THE DEVELOPING LAKE
EFFECT CONVERGENCE...AND HAVE ALREADY SEEN RADAR TRENDS AND
OBSERVATIONS/REPORTS SUPPORTING LOCALLY HEAVY SNOW. SO HAVE
TRENDED MORE PESSIMISTIC WITH THE TAF...WITH TEMPORARY LIFR
CONDITIONS IN SNOW SHOWERS. BRIEF 1/4SM VISIBILITY CERTAINLY IS
POSSIBLE IN THE HEAVIER SNOW BANDS AND ALREADY HAS BEEN BRIEFLY
OBSERVED AT MDW. VERTICAL VISIBILITY HAS NOT DROPPED BELOW 800 FT
THUS FAR...AND WOULD NOT EXPECT TO SEE THAT GET MUCH LOWER...BUT
STILL IMPACTS WILL BE FELT AT THE AIRPORTS DUE TO QUICK BURSTS OF
LOWER VISIBILITY AND SNOW ACCUMULATION.

GIVEN THE SMALL SCALE NATURE OF SPECIFIC SNOW BANDS AND THE
CHALLENGE TO PREDICT IF THIS EVENT WILL REMAIN AS SEVERAL SNOW
BANDS OR DEVELOP INTO ONE OR TWO MORE FOCUSED ONES BY
DAYBREAK...CONFIDENCE ON EXACT TIMING OF LOWER VISIBILITY IS LOW
AND THUS FEEL IT PRUDENT TO REMAIN WITH LONGER TEMPO TIMES. ALSO
FOR SNOW ACCUMULATIONS AT THE AIRPORTS...BEST FORECAST IS THAT
ADDITIONAL ACCUMULATIONS AFTER 06Z OF ONE TO TWO AND A HALF INCHES
FOR MDW AND MAYBE A LITTLE HIGHER AT GYY MAINLY COMING LATER THIS
MORNING...WITH AROUND ONE INCH OR A LITTLE MORE AT ORD.
CONFIDENCE IS LOW-MEDIUM ON THESE ACCUMULATIONS GIVEN THE NARROW
NATURE OF THE BANDING.

THE LAKE EFFECT SNOW BANDS WILL PIVOT MORE INTO NORTHWEST INDIANA
BY EARLY AFTERNOON AND GRADUALLY EASE EASTWARD INTO EVENING.
CLOUDS IN THE WAKE SHOULD LIFT AND SCATTER ACROSS NORTHERN
ILLINOIS...WITH RFD EXPERIENCING THIS IMPROVEMENT ALREADY THIS
MORNING.

NORTH-NORTHEAST WINDS AT ORD AND MDW WILL PIVOT MORE NORTHERLY IN
ASSOCIATION WITH THE LAKE EFFECT CONVERGENCE. WHEN EXACTLY THIS
HAPPENS IS CHALLENGING TO SAY...BUT IT ALREADY SEEMS TO BE BEING
OBSERVED AS OF 06Z AT ORD...SO NEAR DUE NORTH WINDS MAY BE MORE
COMMON AT ORD THROUGH MUCH OF THIS MORNING.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN SNOW SHOWERS THROUGH AT LEAST 13Z-15Z AT ORD AND THROUGH
  MUCH OF THE MORNING AT MDW. MEDIUM-HIGH IN VISIBILITY ALTERNATING
  BETWEEN MAINLY IFR AND LIFR ESPECIALLY AT MDW.

* HIGH ON NORTH-NORTHEAST WINDS AT MDW THROUGH AT LEAST MID
  MORNING. LOW-MEDIUM AT ORD WHERE THEY ARE LIKELY TO BE CLOSER TO
  DUE NORTH AT TIMES THROUGH THE MORNING. HIGH ON WIND SPEEDS AND
  OCCASIONAL GUSTS.

* MEDIUM-HIGH ON CIGS AND THAT THEY WILL REMAIN ABOVE 700 FT.


//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

MTF/RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260511
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1111 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten






000
FXUS63 KILX 260511
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1111 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten







000
FXUS63 KILX 260511
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1111 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten







000
FXUS63 KILX 260511
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1111 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten







000
FXUS63 KILX 260511
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1111 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten







000
FXUS63 KILX 260511
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1111 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1111 PM CST WED FEB 25 2015

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten







000
FXUS63 KLOT 260314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
914 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW/SNOW SHOWERS CONTINUING THROUGH MID TO LATE THURSDAY
  MORNING. IFR VSBY LIKELY...WITH OCCASIONAL LIFR VSBY OVERNIGHT
  INTO POSSIBLY THURSDAY MORNING IF/WHEN HEAVIER LAKE EFFECT SNOW
  SHOWERS DIRECTLY IMPACT TERMINALS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW AND TIMING
  OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.

RC

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

* HIGH IN PREDOMINANTLY IFR VSBY AND MVFR CIGS TONIGHT INTO
  THURSDAY MORNING...LOW IN EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM-HIGH IN OCCASIONAL LIFR VSBY OVERNIGHT...LOW IN LIFR VSBY
  LINGERING INTO THURSDAY MORNING.

* MEDIUM IN OCCASIONAL IFR CIGS IN HEAVIER SNOW
  OVERNIGHT...ESPECIALLY AT MDW.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
914 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW/SNOW SHOWERS CONTINUING THROUGH MID TO LATE THURSDAY
  MORNING. IFR VSBY LIKELY...WITH OCCASIONAL LIFR VSBY OVERNIGHT
  INTO POSSIBLY THURSDAY MORNING IF/WHEN HEAVIER LAKE EFFECT SNOW
  SHOWERS DIRECTLY IMPACT TERMINALS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW AND TIMING
  OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.

RC

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

* HIGH IN PREDOMINANTLY IFR VSBY AND MVFR CIGS TONIGHT INTO
  THURSDAY MORNING...LOW IN EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM-HIGH IN OCCASIONAL LIFR VSBY OVERNIGHT...LOW IN LIFR VSBY
  LINGERING INTO THURSDAY MORNING.

* MEDIUM IN OCCASIONAL IFR CIGS IN HEAVIER SNOW
  OVERNIGHT...ESPECIALLY AT MDW.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
914 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW/SNOW SHOWERS CONTINUING THROUGH MID TO LATE THURSDAY
  MORNING. IFR VSBY LIKELY...WITH OCCASIONAL LIFR VSBY OVERNIGHT
  INTO POSSIBLY THURSDAY MORNING IF/WHEN HEAVIER LAKE EFFECT SNOW
  SHOWERS DIRECTLY IMPACT TERMINALS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW AND TIMING
  OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.

RC

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

* HIGH IN PREDOMINANTLY IFR VSBY AND MVFR CIGS TONIGHT INTO
  THURSDAY MORNING...LOW IN EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM-HIGH IN OCCASIONAL LIFR VSBY OVERNIGHT...LOW IN LIFR VSBY
  LINGERING INTO THURSDAY MORNING.

* MEDIUM IN OCCASIONAL IFR CIGS IN HEAVIER SNOW
  OVERNIGHT...ESPECIALLY AT MDW.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
914 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW/SNOW SHOWERS CONTINUING THROUGH MID TO LATE THURSDAY
  MORNING. IFR VSBY LIKELY...WITH OCCASIONAL LIFR VSBY OVERNIGHT
  INTO POSSIBLY THURSDAY MORNING IF/WHEN HEAVIER LAKE EFFECT SNOW
  SHOWERS DIRECTLY IMPACT TERMINALS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW AND TIMING
  OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.

RC

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

* HIGH IN PREDOMINANTLY IFR VSBY AND MVFR CIGS TONIGHT INTO
  THURSDAY MORNING...LOW IN EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM-HIGH IN OCCASIONAL LIFR VSBY OVERNIGHT...LOW IN LIFR VSBY
  LINGERING INTO THURSDAY MORNING.

* MEDIUM IN OCCASIONAL IFR CIGS IN HEAVIER SNOW
  OVERNIGHT...ESPECIALLY AT MDW.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260259
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
859 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 600 PM CST WED FEB 25 2015

Snow is moving into the area and has begun to effect PIA. Will
start in BMI around 01z, and then around 04z at SPI/DEC/BMI.
Conditions will drop to IFR at PIA and BMI first and then at the
other sites when it starts, but improve during the overnight hours
as the system weakens. IFR conditions could last longer at PIA and
BMI, but as the system weakens and drops south, they too will
improve to MVFR conditions. MVFR conditions are expected at all
sites the remainder of the TAF period, based cigs only. Could be
some very light snow or flurries during the remainder of the
morning and into the afternoon, so keeping that in all TAFs. Winds
will be east to northeast and then become northerly tomorrow and
increase in speeds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten






000
FXUS63 KILX 260259
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
859 PM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 859 PM CST WED FEB 25 2015

Light snow continues across the area and is slowly moving south.
The system will continue to weaken as it moves south and east
overnight. Current forecast has a good handle on trends, so no
update required at this time. Winter weather advisory will
continue as is.

&&

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 600 PM CST WED FEB 25 2015

Snow is moving into the area and has begun to effect PIA. Will
start in BMI around 01z, and then around 04z at SPI/DEC/BMI.
Conditions will drop to IFR at PIA and BMI first and then at the
other sites when it starts, but improve during the overnight hours
as the system weakens. IFR conditions could last longer at PIA and
BMI, but as the system weakens and drops south, they too will
improve to MVFR conditions. MVFR conditions are expected at all
sites the remainder of the TAF period, based cigs only. Could be
some very light snow or flurries during the remainder of the
morning and into the afternoon, so keeping that in all TAFs. Winds
will be east to northeast and then become northerly tomorrow and
increase in speeds.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

UPDATE...Auten
SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten






000
FXUS63 KLOT 260008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
608 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH MID TO LATE THURSDAY MORNING. IFR VSBY
  LIKELY...WITH OCCASIONAL LIFR VSBY EXPECTED THIS EVENING.

* LIFR VSBY POSSIBLE IN LAKE EFFECT SNOW LATE TONIGHT INTO
  THURSDAY MORNING IF TERMINALS ARE DIRECRTLY IMPACTED BY HEAVIER
  SNOW BANDS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* TIMING OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.


RC


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

* HIGH IN MVFR CIGS AND PREDOMINANTLY IFR VSBY TONIGHT INTO
  THURSDAY MORNING...LOW ON EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING. LOW IN LIFR VSBY IN
  LAKE EFFECT SNOW LATE TONIGHT INTO THURSDAY MORNING.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
608 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH MID TO LATE THURSDAY MORNING. IFR VSBY
  LIKELY...WITH OCCASIONAL LIFR VSBY EXPECTED THIS EVENING.

* LIFR VSBY POSSIBLE IN LAKE EFFECT SNOW LATE TONIGHT INTO
  THURSDAY MORNING IF TERMINALS ARE DIRECRTLY IMPACTED BY HEAVIER
  SNOW BANDS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* TIMING OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.


RC


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

* HIGH IN MVFR CIGS AND PREDOMINANTLY IFR VSBY TONIGHT INTO
  THURSDAY MORNING...LOW ON EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING. LOW IN LIFR VSBY IN
  LAKE EFFECT SNOW LATE TONIGHT INTO THURSDAY MORNING.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
608 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH MID TO LATE THURSDAY MORNING. IFR VSBY
  LIKELY...WITH OCCASIONAL LIFR VSBY EXPECTED THIS EVENING.

* LIFR VSBY POSSIBLE IN LAKE EFFECT SNOW LATE TONIGHT INTO
  THURSDAY MORNING IF TERMINALS ARE DIRECRTLY IMPACTED BY HEAVIER
  SNOW BANDS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* TIMING OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.


RC


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

* HIGH IN MVFR CIGS AND PREDOMINANTLY IFR VSBY TONIGHT INTO
  THURSDAY MORNING...LOW ON EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING. LOW IN LIFR VSBY IN
  LAKE EFFECT SNOW LATE TONIGHT INTO THURSDAY MORNING.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
608 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH MID TO LATE THURSDAY MORNING. IFR VSBY
  LIKELY...WITH OCCASIONAL LIFR VSBY EXPECTED THIS EVENING.

* LIFR VSBY POSSIBLE IN LAKE EFFECT SNOW LATE TONIGHT INTO
  THURSDAY MORNING IF TERMINALS ARE DIRECRTLY IMPACTED BY HEAVIER
  SNOW BANDS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* TIMING OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.


RC


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

* HIGH IN MVFR CIGS AND PREDOMINANTLY IFR VSBY TONIGHT INTO
  THURSDAY MORNING...LOW ON EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING. LOW IN LIFR VSBY IN
  LAKE EFFECT SNOW LATE TONIGHT INTO THURSDAY MORNING.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
608 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH MID TO LATE THURSDAY MORNING. IFR VSBY
  LIKELY...WITH OCCASIONAL LIFR VSBY EXPECTED THIS EVENING.

* LIFR VSBY POSSIBLE IN LAKE EFFECT SNOW LATE TONIGHT INTO
  THURSDAY MORNING IF TERMINALS ARE DIRECRTLY IMPACTED BY HEAVIER
  SNOW BANDS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* TIMING OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.


RC


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

* HIGH IN MVFR CIGS AND PREDOMINANTLY IFR VSBY TONIGHT INTO
  THURSDAY MORNING...LOW ON EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING. LOW IN LIFR VSBY IN
  LAKE EFFECT SNOW LATE TONIGHT INTO THURSDAY MORNING.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260008
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
608 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH MID TO LATE THURSDAY MORNING. IFR VSBY
  LIKELY...WITH OCCASIONAL LIFR VSBY EXPECTED THIS EVENING.

* LIFR VSBY POSSIBLE IN LAKE EFFECT SNOW LATE TONIGHT INTO
  THURSDAY MORNING IF TERMINALS ARE DIRECRTLY IMPACTED BY HEAVIER
  SNOW BANDS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* TIMING OF CIG IMPROVEMENTS ON THURSDAY.

RC

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

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.


RC


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

* HIGH IN MVFR CIGS AND PREDOMINANTLY IFR VSBY TONIGHT INTO
  THURSDAY MORNING...LOW ON EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING. LOW IN LIFR VSBY IN
  LAKE EFFECT SNOW LATE TONIGHT INTO THURSDAY MORNING.

* MEDIUM-HIGH IN WIND TRENDS.

RC

//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 260000
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
600 PM CST Wed Feb 25 2015

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 600 PM CST WED FEB 25 2015

Snow is moving into the area and has begun to effect PIA. Will
start in BMI around 01z, and then around 04z at SPI/DEC/BMI.
Conditions will drop to IFR at PIA and BMI first and then at the
other sites when it starts, but improve during the overnight hours
as the system weakens. IFR conditions could last longer at PIA and
BMI, but as the system weakens and drops south, they too will
improve to MVFR conditions. MVFR conditions are expected at all
sites the remainder of the TAF period, based cigs only. Could be
some very light snow or flurries during the remainder of the
morning and into the afternoon, so keeping that in all TAFs. Winds
will be east to northeast and then become northerly tomorrow and
increase in speeds.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten






000
FXUS63 KILX 260000
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
600 PM CST Wed Feb 25 2015

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 600 PM CST WED FEB 25 2015

Snow is moving into the area and has begun to effect PIA. Will
start in BMI around 01z, and then around 04z at SPI/DEC/BMI.
Conditions will drop to IFR at PIA and BMI first and then at the
other sites when it starts, but improve during the overnight hours
as the system weakens. IFR conditions could last longer at PIA and
BMI, but as the system weakens and drops south, they too will
improve to MVFR conditions. MVFR conditions are expected at all
sites the remainder of the TAF period, based cigs only. Could be
some very light snow or flurries during the remainder of the
morning and into the afternoon, so keeping that in all TAFs. Winds
will be east to northeast and then become northerly tomorrow and
increase in speeds.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten







000
FXUS63 KILX 260000
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
600 PM CST Wed Feb 25 2015

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 600 PM CST WED FEB 25 2015

Snow is moving into the area and has begun to effect PIA. Will
start in BMI around 01z, and then around 04z at SPI/DEC/BMI.
Conditions will drop to IFR at PIA and BMI first and then at the
other sites when it starts, but improve during the overnight hours
as the system weakens. IFR conditions could last longer at PIA and
BMI, but as the system weakens and drops south, they too will
improve to MVFR conditions. MVFR conditions are expected at all
sites the remainder of the TAF period, based cigs only. Could be
some very light snow or flurries during the remainder of the
morning and into the afternoon, so keeping that in all TAFs. Winds
will be east to northeast and then become northerly tomorrow and
increase in speeds.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten






000
FXUS63 KILX 260000
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
600 PM CST Wed Feb 25 2015

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.

&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 600 PM CST WED FEB 25 2015

Snow is moving into the area and has begun to effect PIA. Will
start in BMI around 01z, and then around 04z at SPI/DEC/BMI.
Conditions will drop to IFR at PIA and BMI first and then at the
other sites when it starts, but improve during the overnight hours
as the system weakens. IFR conditions could last longer at PIA and
BMI, but as the system weakens and drops south, they too will
improve to MVFR conditions. MVFR conditions are expected at all
sites the remainder of the TAF period, based cigs only. Could be
some very light snow or flurries during the remainder of the
morning and into the afternoon, so keeping that in all TAFs. Winds
will be east to northeast and then become northerly tomorrow and
increase in speeds.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

SHORT TERM...25
LONG TERM...Shimon
AVIATION...Auten







000
FXUS63 KLOT 252208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH THURSDAY MORNING...WITH IFR VSBY THROUGH
  THIS EVENING. PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB/RC

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

DUE TO LAKE ENHANCEMENT OF THE LIGHT SNOW...MDW HAD ALREADY
DROPPED TO IFR VSBY...WHILE ORD REMAINED MVFR A BIT LONGER. BASED
ON LATEST 1 MINUTE DATA TRENDS AT ORD...VSBY APPEARS THAT IT IS
DROPPING TO PREVAILING IFR AT ORD AND IS LIKELY TO REMAIN IFR
THROUGH THE EVENING. LIFR VSBY REMAINS POSSIBLE THIS EVENING...BUT
MAY DEPEND ON INTENSITY OF LAKE EFFECT/LAKE ENHANCED SNOW...AS
HEAVIER SYSTEM SNOW WILL REMAIN SOUTH OF THE TERMINALS.

RC

FROM 18Z...

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW LONG IFR WILL
  LAST.

* LOW-MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH THURSDAY MORNING...WITH IFR VSBY THROUGH
  THIS EVENING. PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB/RC

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

DUE TO LAKE ENHANCEMENT OF THE LIGHT SNOW...MDW HAD ALREADY
DROPPED TO IFR VSBY...WHILE ORD REMAINED MVFR A BIT LONGER. BASED
ON LATEST 1 MINUTE DATA TRENDS AT ORD...VSBY APPEARS THAT IT IS
DROPPING TO PREVAILING IFR AT ORD AND IS LIKELY TO REMAIN IFR
THROUGH THE EVENING. LIFR VSBY REMAINS POSSIBLE THIS EVENING...BUT
MAY DEPEND ON INTENSITY OF LAKE EFFECT/LAKE ENHANCED SNOW...AS
HEAVIER SYSTEM SNOW WILL REMAIN SOUTH OF THE TERMINALS.

RC

FROM 18Z...

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW LONG IFR WILL
  LAST.

* LOW-MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH THURSDAY MORNING...WITH IFR VSBY THROUGH
  THIS EVENING. PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB/RC

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

DUE TO LAKE ENHANCEMENT OF THE LIGHT SNOW...MDW HAD ALREADY
DROPPED TO IFR VSBY...WHILE ORD REMAINED MVFR A BIT LONGER. BASED
ON LATEST 1 MINUTE DATA TRENDS AT ORD...VSBY APPEARS THAT IT IS
DROPPING TO PREVAILING IFR AT ORD AND IS LIKELY TO REMAIN IFR
THROUGH THE EVENING. LIFR VSBY REMAINS POSSIBLE THIS EVENING...BUT
MAY DEPEND ON INTENSITY OF LAKE EFFECT/LAKE ENHANCED SNOW...AS
HEAVIER SYSTEM SNOW WILL REMAIN SOUTH OF THE TERMINALS.

RC

FROM 18Z...

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW LONG IFR WILL
  LAST.

* LOW-MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW CONTINUING THROUGH THURSDAY MORNING...WITH IFR VSBY THROUGH
  THIS EVENING. PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB/RC

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

DUE TO LAKE ENHANCEMENT OF THE LIGHT SNOW...MDW HAD ALREADY
DROPPED TO IFR VSBY...WHILE ORD REMAINED MVFR A BIT LONGER. BASED
ON LATEST 1 MINUTE DATA TRENDS AT ORD...VSBY APPEARS THAT IT IS
DROPPING TO PREVAILING IFR AT ORD AND IS LIKELY TO REMAIN IFR
THROUGH THE EVENING. LIFR VSBY REMAINS POSSIBLE THIS EVENING...BUT
MAY DEPEND ON INTENSITY OF LAKE EFFECT/LAKE ENHANCED SNOW...AS
HEAVIER SYSTEM SNOW WILL REMAIN SOUTH OF THE TERMINALS.

RC

FROM 18Z...

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW LONG IFR WILL
  LAST.

* LOW-MEDIUM IN OCCASIONAL LIFR VSBY THIS EVENING.

RC

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252128
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
328 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 21Z...

* SNOW CONTINUING THROUGH THURSDAY MORNING. IFR VSBY LIKELY BY
  ABOUT 22Z WITH MVFR CIGS BY A. PERIODS OF LIFR VIS POSSIBLE
  THIS EVENING.

KJB/RC

//DISCUSSION...UPDATED 21Z...

HAVE MOVED UP TIMING OF IFR VSBY IN SNOW IN TAFS BASED ON CURRENT
RADAR AND OBSERVATIONAL TRENDS. ORD AND MDW ARE CURRENTLY AT MVFR
VSBY AND SHOULD FALL TO IFR VSBY BY ABOUT 22Z...REMAINING IFR VSBY
FOR SEVERAL HOURS WITH LIFR POSSIBLE THIS EVENING.

RC

FROM 18Z...

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 21Z...

* HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW LONG IFR
  OR LIFR WILL LAST.

KJB/RC

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252128
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
328 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 21Z...

* SNOW CONTINUING THROUGH THURSDAY MORNING. IFR VSBY LIKELY BY
  ABOUT 22Z WITH MVFR CIGS BY A. PERIODS OF LIFR VIS POSSIBLE
  THIS EVENING.

KJB/RC

//DISCUSSION...UPDATED 21Z...

HAVE MOVED UP TIMING OF IFR VSBY IN SNOW IN TAFS BASED ON CURRENT
RADAR AND OBSERVATIONAL TRENDS. ORD AND MDW ARE CURRENTLY AT MVFR
VSBY AND SHOULD FALL TO IFR VSBY BY ABOUT 22Z...REMAINING IFR VSBY
FOR SEVERAL HOURS WITH LIFR POSSIBLE THIS EVENING.

RC

FROM 18Z...

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 21Z...

* HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW LONG IFR
  OR LIFR WILL LAST.

KJB/RC

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252100
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252100
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252100
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 252056
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
256 PM CST Wed Feb 25 2015

.SHORT TERM...(Tonight)
ISSUED AT 256 PM CST WED FEB 25 2015

Alberta clipper low was centered in extreme SE IA at 19z.
Isentropic lift to the N/NE of this feature was producing a wide
swath of snow across IA and into NW IL.  Within the broad snow band
which had widespread 1-2 mile visibilities, bands of heavier
snowfall rates with visibilities down to 1/4 mile in parts of
central/eastern IA, were associated with significant frontogenetical
forcing in the 700-800 MB layer.  As the entire system shifts
southeast this evening and overnight, snow will overspread the CWA
from north to south.  The first flakes have been observed in
Galesburg at 130 PM, so the lift is efficient at overcoming the
initial dry low levels.  Vertical temperature profile looks to support
dendritic growth mainly north of a Canton to Bloomington line this
evening (especially before stronger frontogenesis weakens later this
evening), so have higher snowfall rates (14:1 SLR) through 06z in
this area.  25/12z guidance and more recent hi-res model runs have
shown a slight northeast shift to the track of the surface and mid
level features.  As a result, have expanded winter weather advisory
east to include Marshall, Woodford, and McLean counties.  Advisory
runs through 15z Thu northwest of a Jacksonville to Bloomington line
for 2 to 4 inch totals with isolated higher amounts in the far NW
towards Knox Co.  The weakening trend expected overnight should allow
for a gradual decrease of snowfall amounts to the southeast, with up
to an inch or two down to the I-72 corridor, and then under a half
inch south of I-70, by daybreak.


&&

.LONG TERM...(Thursday through Wednesday)
ISSUED AT 256 PM CST WED FEB 25 2015

The clipper system will dissipate Thursday morning as it departs to
the east. However, a secondary shortwave over southern Saskatchewan
will quickly follow on Thursday, helping to keep light snow going
during the day. Moisture will be very limited on Thursday, so any
additional accumulation should remain less than a half inch. Snow
will come to an end from west to east during the afternoon.

A reinforcing shot of Arctic air will arrive Thursday night as a
1041mb surface high progresses southward into Illinois. There will
be enough wind through the night to push wind chill readings below
-15F in central IL north of I-70, so we may need a wind chill
advisory for late Thur night into Friday morning. Low temps will
likely drop below guidance numbers with a fresh snow cover in much
of the area. Likewise, highs on Friday will struggle to climb into
the teens. The Arctic high will slide east Friday night, keeping
very cold conditions in place through Sat morning. Winds will
shift to the ESE behind the ridge axis on Saturday morning, which
may be enough to put wind chills down around -15F in our northern
counties.

As the high departs to the east on Saturday, a shift in the upper
pattern will begin to develop. The deep persistent trough in the
eastern CONUS will lift to the northeast and a trough will develop
along the western states. That will allow upper level ridging to
progress toward the Mississippi River Valley. The rising heights
associated with that ridge will signal a warming trend, and a
northward progression of a baroclinic zone into Illinois. A
southwest flow aloft along that zone will help to keep the frontal
region nearly stationary across southern Illinois for several days.
The models are advertising several periods of precipitation to
develop during that time, as shortwaves move northeast along that
baroclinic zone.

The first push of significant precip looks to arrive Saturday night
and linger into Sunday night. The precip should start out as all
snow and remain snow until Sunday afternoon, when some rain possibly
develops south of I-70. There appears to be enough frontogenetical
forcing and deep enough moisture to support the accumulation of
several inches of snow in our forecast area, especially north of
I-70 where precip should remain all snow until the system departs
Sunday night. Any change to rain south of I-70 would diminish snow
totals there. Still, slippery travel conditions appear likely from
Sat night into Sunday night.

A lull in the precip is forecast for late Sunday night and Monday,
as dry surface high pressure passes across Illinois.

The next wave of precip is projected for Monday night and Tuesday,
as low pressure progresses from northern Texas and up the Ohio River
Valley. A much stronger surge of warm air is indicated ahead of the
low pressure center, especially aloft in the 900-800mb layer. The
precip should start out as snow Monday night ahead of the low center.
Model consensus has the low crossing southern IL on Tuesday, which
could cause a transition from snow to rain across at least the
southern half of our forecast area. Depending on how cold the
surface temperatures remain Tuesday morning, we could see a period
of freezing rain somewhere north of I-72 during that transition.
NW counties could remain all snow, and see several inches of
accumulation, while southeast areas could see between a half inch
and one inch of rainfall. Due to model differences with warm air
and the track of the low, we will just mention rain or snow in
most areas on Tuesday for now.

Another push of cold air is forecast behind that system for
Wednesday and Wed night, but no precipitation should occur during
that time.


&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 1149 AM CST WED FEB 25 2015

VFR conditions early this afternoon will deteriorate from the
northwest late this afternoon and evening, as accumulating snow
moves in from the northwest. The system will weaken as it shifts
southeast, so the lowest IFR conditions are expected at KPIA, with
periods of visibility as low as 1/4 SM in heavy snow this evening,
while KBMI is expected to drop as low as 1/2 SM. Farther south
predominant visibilities are expected around 1 SM late this
evening and overnight. IFR cloud cover will accompany the
snowfall. The snow will taper off from the NW late tonight through
Thursday morning with corresponding rises in vis and slight rises
in ceiling. East winds near/under 10 kts this afternoon will
increase to 10-15 kt and turn more northerly overnight and through
morning, as low pressure tracks towards SE Missouri.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 9 AM CST Thursday FOR ILZ027>031-
036>038-040-041-047-049-050.

&&

$$

SHORT TERM...25
LONG TERM...Shimon
AVIATION...25







000
FXUS63 KLOT 252024
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
224 PM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

.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 251948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
148 PM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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 251948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
148 PM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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 251948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
148 PM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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 251948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
148 PM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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
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000
FXUS63 KLOT 251948
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
148 PM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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 251749
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1149 AM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 949 AM CST WED FEB 25 2015

9 AM surface map indicated 1006 MB Alberta clipper over eastern
Nebraska with a large area of snow northeast of this feature from
South Dakota into central and northeast Iowa. Main forecast issue
through this afternoon is timing of snow onset in the northwest.
Based on 12z ILX/DVN soundings and KDVN radar returns, there is
plenty of low to mid level dry air to overcome before precip
reaches the surface. Nearest sites reporting snow are Marshalltown
and Waterloo IA. As the system slides southeast, top-down
saturation will occur from the NW, and latest hi-res guidance
suggests snow will begin to reach the ground north of Peoria in a
3-5 PM time frame. Accumulations will likely begin quickly due to
cold surface temperatures and setting sun, in addition to strong
lift on the leading edge of the system. Before that, a period of
mostly sunny skies will affect the central and southern CWA later
this morning and afternoon, ahead of the increasing cloud cover.
Have raised maxes a few degrees due to temps already rising into
the mid/upper 20s over parts of the CWA.

&&

.SHORT TERM...(Today)
ISSUED AT 327 AM CST WED FEB 25 2015

08z/2am surface analysis shows 1004mb low over South Dakota, with
snow currently falling across the eastern Dakotas and far southwest
Minnesota.  Clipper system is expected to track southeastward to
near Kansas City by evening, resulting in snow spreading into
west-central Illinois later today.  00z KILX upper air sounding
shows plenty of dry air that will have to be overcome before precip
reaches the ground, so despite fast movement of system think snow
will hold off until after 21z.  Based on NAM time-height
cross-sections, it appears profile does not fully moisten at KPIA
until 00z, but this may be a bit slow given current speed of
system.  Have therefore gone with dry conditions across the board
through mid-afternoon, then have introduced PoPs across the Illinois
River Valley between 21z and 00z.  Once snow overcomes dry air, it
will rapidly begin accumulating, with up to 1 inch expected around
the Galesburg area by 00z.  Elsewhere around central Illinois, cold
and dry conditions will prevail with high temperatures mainly in
the middle to upper 20s.

&&

.LONG TERM...(Tonight through Tuesday)
ISSUED AT 327 AM CST WED FEB 25 2015

While clipper system will be dissipating as it tracks into the
region tonight, lift will be strong enough to support a period of
moderate snow across the western half of the CWA.  Time-height
cross-sections indicate strongest lift within the dendritic growth
zone between 00z and 04z at KPIA, then slightly later further east and
south.  Once profile moistens sufficiently, think snow will come
down at a moderate to heavy rate for a 3 to 5 hour time frame this
evening into the early parts of the overnight hours.  This will
result in a snow accumulation of 2 to 4 inches across the Illinois
River Valley, where a Winter Weather Advisory will be issued.  The
snow will be slow to spread southeastward across the remainder of
the area and will likely not reach the I-70 corridor until after
midnight.  Lift will weaken as well, so snow totals will steadily
decrease toward the Indiana border.  Am expecting around 2 inches
along the I-55 corridor...around 1 inch near I-57...and less than 1
inch in the Wabash River Valley.  Initial system will dissipate on
Thursday: however, a secondary short-wave currently over northern
Manitoba will drop southward into the area and provide enough lift
to keep light snow chances going through at least the first half of
the day.  Minor additional accumulations of less than one half inch
are anticipated.

Once the clipper departs, another shot of bitterly cold air will
arrive for the end of the week.  With clear skies and diminishing
winds over a fresh snow cover, have undercut guidance numbers for
low temps Thursday night with readings once again dropping below
zero in most locations.  Cold/dry weather will continue on Friday as
highs struggle to reach the teens.

After that, the weather becomes more active as a major pattern shift
gets underway.  As has been advertised for several days, the
persistent upper low over southern Canada will lift to the north,
allowing a southwesterly flow pattern to develop across the central
CONUS this weekend into next week.  This will result in warming
temps and a prolonged period of unsettled weather.  Models are still
having a hard time adjusting to the pattern change, although they
are now beginning to come into better focus concerning timing of
individual waves.  As flow becomes southwesterly, baroclinic zone
will lift into the Midwest and become nearly stationary for several
days.  As upper short-waves track along the boundary, periodic
precip chances will occur across Illinois from Saturday night
through Tuesday.  Initial wave of precip Saturday night into Sunday
will mostly be in the form of snow, with a few inches possible
across at least the northern two-thirds of the CWA.  Models are now
in good agreement that this wave will exit the region, leading to a
lull in the precip chances late Sunday night into Monday.  Have
removed PoPs on Monday accordingly.  After that, a much stronger
wave will approach from the southwest by Tuesday, potentially
bringing another round of precipitation.  Model solutions vary
considerably, with the GFS being much faster than either the ECMWF
or GEM.  Consensus brings low pressure across Illinois on Tuesday,
resulting in warmer conditions and the potential for rain or a
rain/snow mix.  Will have to keep an eye on the northern CWA as the
precip begins, as GFS forecast soundings suggest the potential for a
period of freezing rain late Monday night/Tuesday morning.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 1149 AM CST WED FEB 25 2015

VFR conditions early this afternoon will deteriorate from the
northwest late this afternoon and evening, as accumulating snow
moves in from the northwest. The system will weaken as it shifts
southeast, so the lowest IFR conditions are expected at KPIA, with
periods of visibility as low as 1/4 SM in heavy snow this evening,
while KBMI is expected to drop as low as 1/2 SM. Farther south
predominant visibilities are expected around 1 SM late this
evening and overnight. IFR cloud cover will accompany the
snowfall. The snow will taper off from the NW late tonight through
Thursday morning with corresponding rises in vis and slight rises
in ceiling. East winds near/under 10 kts this afternoon will
increase to 10-15 kt and turn more northerly overnight and through
morning, as low pressure tracks towards SE Missouri.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY from 4 PM this afternoon to 9 AM CST
Thursday FOR ILZ027>029-036-037-040-041-047-049-050.

&&

$$

UPDATE...25
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...25







000
FXUS63 KILX 251749
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1149 AM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 949 AM CST WED FEB 25 2015

9 AM surface map indicated 1006 MB Alberta clipper over eastern
Nebraska with a large area of snow northeast of this feature from
South Dakota into central and northeast Iowa. Main forecast issue
through this afternoon is timing of snow onset in the northwest.
Based on 12z ILX/DVN soundings and KDVN radar returns, there is
plenty of low to mid level dry air to overcome before precip
reaches the surface. Nearest sites reporting snow are Marshalltown
and Waterloo IA. As the system slides southeast, top-down
saturation will occur from the NW, and latest hi-res guidance
suggests snow will begin to reach the ground north of Peoria in a
3-5 PM time frame. Accumulations will likely begin quickly due to
cold surface temperatures and setting sun, in addition to strong
lift on the leading edge of the system. Before that, a period of
mostly sunny skies will affect the central and southern CWA later
this morning and afternoon, ahead of the increasing cloud cover.
Have raised maxes a few degrees due to temps already rising into
the mid/upper 20s over parts of the CWA.

&&

.SHORT TERM...(Today)
ISSUED AT 327 AM CST WED FEB 25 2015

08z/2am surface analysis shows 1004mb low over South Dakota, with
snow currently falling across the eastern Dakotas and far southwest
Minnesota.  Clipper system is expected to track southeastward to
near Kansas City by evening, resulting in snow spreading into
west-central Illinois later today.  00z KILX upper air sounding
shows plenty of dry air that will have to be overcome before precip
reaches the ground, so despite fast movement of system think snow
will hold off until after 21z.  Based on NAM time-height
cross-sections, it appears profile does not fully moisten at KPIA
until 00z, but this may be a bit slow given current speed of
system.  Have therefore gone with dry conditions across the board
through mid-afternoon, then have introduced PoPs across the Illinois
River Valley between 21z and 00z.  Once snow overcomes dry air, it
will rapidly begin accumulating, with up to 1 inch expected around
the Galesburg area by 00z.  Elsewhere around central Illinois, cold
and dry conditions will prevail with high temperatures mainly in
the middle to upper 20s.

&&

.LONG TERM...(Tonight through Tuesday)
ISSUED AT 327 AM CST WED FEB 25 2015

While clipper system will be dissipating as it tracks into the
region tonight, lift will be strong enough to support a period of
moderate snow across the western half of the CWA.  Time-height
cross-sections indicate strongest lift within the dendritic growth
zone between 00z and 04z at KPIA, then slightly later further east and
south.  Once profile moistens sufficiently, think snow will come
down at a moderate to heavy rate for a 3 to 5 hour time frame this
evening into the early parts of the overnight hours.  This will
result in a snow accumulation of 2 to 4 inches across the Illinois
River Valley, where a Winter Weather Advisory will be issued.  The
snow will be slow to spread southeastward across the remainder of
the area and will likely not reach the I-70 corridor until after
midnight.  Lift will weaken as well, so snow totals will steadily
decrease toward the Indiana border.  Am expecting around 2 inches
along the I-55 corridor...around 1 inch near I-57...and less than 1
inch in the Wabash River Valley.  Initial system will dissipate on
Thursday: however, a secondary short-wave currently over northern
Manitoba will drop southward into the area and provide enough lift
to keep light snow chances going through at least the first half of
the day.  Minor additional accumulations of less than one half inch
are anticipated.

Once the clipper departs, another shot of bitterly cold air will
arrive for the end of the week.  With clear skies and diminishing
winds over a fresh snow cover, have undercut guidance numbers for
low temps Thursday night with readings once again dropping below
zero in most locations.  Cold/dry weather will continue on Friday as
highs struggle to reach the teens.

After that, the weather becomes more active as a major pattern shift
gets underway.  As has been advertised for several days, the
persistent upper low over southern Canada will lift to the north,
allowing a southwesterly flow pattern to develop across the central
CONUS this weekend into next week.  This will result in warming
temps and a prolonged period of unsettled weather.  Models are still
having a hard time adjusting to the pattern change, although they
are now beginning to come into better focus concerning timing of
individual waves.  As flow becomes southwesterly, baroclinic zone
will lift into the Midwest and become nearly stationary for several
days.  As upper short-waves track along the boundary, periodic
precip chances will occur across Illinois from Saturday night
through Tuesday.  Initial wave of precip Saturday night into Sunday
will mostly be in the form of snow, with a few inches possible
across at least the northern two-thirds of the CWA.  Models are now
in good agreement that this wave will exit the region, leading to a
lull in the precip chances late Sunday night into Monday.  Have
removed PoPs on Monday accordingly.  After that, a much stronger
wave will approach from the southwest by Tuesday, potentially
bringing another round of precipitation.  Model solutions vary
considerably, with the GFS being much faster than either the ECMWF
or GEM.  Consensus brings low pressure across Illinois on Tuesday,
resulting in warmer conditions and the potential for rain or a
rain/snow mix.  Will have to keep an eye on the northern CWA as the
precip begins, as GFS forecast soundings suggest the potential for a
period of freezing rain late Monday night/Tuesday morning.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 1149 AM CST WED FEB 25 2015

VFR conditions early this afternoon will deteriorate from the
northwest late this afternoon and evening, as accumulating snow
moves in from the northwest. The system will weaken as it shifts
southeast, so the lowest IFR conditions are expected at KPIA, with
periods of visibility as low as 1/4 SM in heavy snow this evening,
while KBMI is expected to drop as low as 1/2 SM. Farther south
predominant visibilities are expected around 1 SM late this
evening and overnight. IFR cloud cover will accompany the
snowfall. The snow will taper off from the NW late tonight through
Thursday morning with corresponding rises in vis and slight rises
in ceiling. East winds near/under 10 kts this afternoon will
increase to 10-15 kt and turn more northerly overnight and through
morning, as low pressure tracks towards SE Missouri.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY from 4 PM this afternoon to 9 AM CST
Thursday FOR ILZ027>029-036-037-040-041-047-049-050.

&&

$$

UPDATE...25
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...25






000
FXUS63 KILX 251749
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1149 AM CST Wed Feb 25 2015

.UPDATE...
ISSUED AT 949 AM CST WED FEB 25 2015

9 AM surface map indicated 1006 MB Alberta clipper over eastern
Nebraska with a large area of snow northeast of this feature from
South Dakota into central and northeast Iowa. Main forecast issue
through this afternoon is timing of snow onset in the northwest.
Based on 12z ILX/DVN soundings and KDVN radar returns, there is
plenty of low to mid level dry air to overcome before precip
reaches the surface. Nearest sites reporting snow are Marshalltown
and Waterloo IA. As the system slides southeast, top-down
saturation will occur from the NW, and latest hi-res guidance
suggests snow will begin to reach the ground north of Peoria in a
3-5 PM time frame. Accumulations will likely begin quickly due to
cold surface temperatures and setting sun, in addition to strong
lift on the leading edge of the system. Before that, a period of
mostly sunny skies will affect the central and southern CWA later
this morning and afternoon, ahead of the increasing cloud cover.
Have raised maxes a few degrees due to temps already rising into
the mid/upper 20s over parts of the CWA.

&&

.SHORT TERM...(Today)
ISSUED AT 327 AM CST WED FEB 25 2015

08z/2am surface analysis shows 1004mb low over South Dakota, with
snow currently falling across the eastern Dakotas and far southwest
Minnesota.  Clipper system is expected to track southeastward to
near Kansas City by evening, resulting in snow spreading into
west-central Illinois later today.  00z KILX upper air sounding
shows plenty of dry air that will have to be overcome before precip
reaches the ground, so despite fast movement of system think snow
will hold off until after 21z.  Based on NAM time-height
cross-sections, it appears profile does not fully moisten at KPIA
until 00z, but this may be a bit slow given current speed of
system.  Have therefore gone with dry conditions across the board
through mid-afternoon, then have introduced PoPs across the Illinois
River Valley between 21z and 00z.  Once snow overcomes dry air, it
will rapidly begin accumulating, with up to 1 inch expected around
the Galesburg area by 00z.  Elsewhere around central Illinois, cold
and dry conditions will prevail with high temperatures mainly in
the middle to upper 20s.

&&

.LONG TERM...(Tonight through Tuesday)
ISSUED AT 327 AM CST WED FEB 25 2015

While clipper system will be dissipating as it tracks into the
region tonight, lift will be strong enough to support a period of
moderate snow across the western half of the CWA.  Time-height
cross-sections indicate strongest lift within the dendritic growth
zone between 00z and 04z at KPIA, then slightly later further east and
south.  Once profile moistens sufficiently, think snow will come
down at a moderate to heavy rate for a 3 to 5 hour time frame this
evening into the early parts of the overnight hours.  This will
result in a snow accumulation of 2 to 4 inches across the Illinois
River Valley, where a Winter Weather Advisory will be issued.  The
snow will be slow to spread southeastward across the remainder of
the area and will likely not reach the I-70 corridor until after
midnight.  Lift will weaken as well, so snow totals will steadily
decrease toward the Indiana border.  Am expecting around 2 inches
along the I-55 corridor...around 1 inch near I-57...and less than 1
inch in the Wabash River Valley.  Initial system will dissipate on
Thursday: however, a secondary short-wave currently over northern
Manitoba will drop southward into the area and provide enough lift
to keep light snow chances going through at least the first half of
the day.  Minor additional accumulations of less than one half inch
are anticipated.

Once the clipper departs, another shot of bitterly cold air will
arrive for the end of the week.  With clear skies and diminishing
winds over a fresh snow cover, have undercut guidance numbers for
low temps Thursday night with readings once again dropping below
zero in most locations.  Cold/dry weather will continue on Friday as
highs struggle to reach the teens.

After that, the weather becomes more active as a major pattern shift
gets underway.  As has been advertised for several days, the
persistent upper low over southern Canada will lift to the north,
allowing a southwesterly flow pattern to develop across the central
CONUS this weekend into next week.  This will result in warming
temps and a prolonged period of unsettled weather.  Models are still
having a hard time adjusting to the pattern change, although they
are now beginning to come into better focus concerning timing of
individual waves.  As flow becomes southwesterly, baroclinic zone
will lift into the Midwest and become nearly stationary for several
days.  As upper short-waves track along the boundary, periodic
precip chances will occur across Illinois from Saturday night
through Tuesday.  Initial wave of precip Saturday night into Sunday
will mostly be in the form of snow, with a few inches possible
across at least the northern two-thirds of the CWA.  Models are now
in good agreement that this wave will exit the region, leading to a
lull in the precip chances late Sunday night into Monday.  Have
removed PoPs on Monday accordingly.  After that, a much stronger
wave will approach from the southwest by Tuesday, potentially
bringing another round of precipitation.  Model solutions vary
considerably, with the GFS being much faster than either the ECMWF
or GEM.  Consensus brings low pressure across Illinois on Tuesday,
resulting in warmer conditions and the potential for rain or a
rain/snow mix.  Will have to keep an eye on the northern CWA as the
precip begins, as GFS forecast soundings suggest the potential for a
period of freezing rain late Monday night/Tuesday morning.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 1149 AM CST WED FEB 25 2015

VFR conditions early this afternoon will deteriorate from the
northwest late this afternoon and evening, as accumulating snow
moves in from the northwest. The system will weaken as it shifts
southeast, so the lowest IFR conditions are expected at KPIA, with
periods of visibility as low as 1/4 SM in heavy snow this evening,
while KBMI is expected to drop as low as 1/2 SM. Farther south
predominant visibilities are expected around 1 SM late this
evening and overnight. IFR cloud cover will accompany the
snowfall. The snow will taper off from the NW late tonight through
Thursday morning with corresponding rises in vis and slight rises
in ceiling. East winds near/under 10 kts this afternoon will
increase to 10-15 kt and turn more northerly overnight and through
morning, as low pressure tracks towards SE Missouri.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY from 4 PM this afternoon to 9 AM CST
Thursday FOR ILZ027>029-036-037-040-041-047-049-050.

&&

$$

UPDATE...25
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...25






000
FXUS63 KLOT 251736
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1136 AM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB


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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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
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WWW.YOUTUBE.COM/NWSCHICAGO





000
FXUS63 KLOT 251736
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1136 AM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB


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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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 251736
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1136 AM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB


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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
205 AM CST

A SLIGHTLY LESS ACTIVE PATTERN OVER THE LAKE IS IN STORE FOR THE
REMAINDER OF THE WEEK AS LOW PRESSURES PASS WELL TO THE SOUTH AND
NORTH. AS ONE LOW DROPS FROM THE CENTRAL PLAINS TO THE MID-
MISSISSIPPI VALLEY TONIGHT INTO THURSDAY MORNING...NORTHEAST TO
NORTH WINDS WILL INCREASE ACROSS MAINLY THE SOUTHERN AND CENTRAL
PARTS OF THE LAKE. IF A CONVERGENT LAKE EFFECT SNOW BAND
DEVELOPS FROM THE OPEN WATERS OF THE LAKE TOWARD NORTHEAST
ILLINOIS THURSDAY MORNING AND NORTHWEST INDIANA LATER THURSDAY AND
THURSDAY EVENING...THEN THERE COULD BE SOME GUSTS TO TOP 25 KT.
WINDS WILL TURN BACK TO THE WEST ON FRIDAY AND SOUTHWEST INTO
SATURDAY. AS HIGH PRESSURE PUSHES IN FOR EARLY NEXT WEEK...A COLD
FRONT IS EXPECTED TO DEVELOP AND CROSS THE LAKE LATE IN THE
WEEKEND. THERE REMAINS A HIGH AMOUNT OF UNCERTAINTY FOR NEXT
WEEK...WITH SOME MODELS INDICATING THE STORM TRACK TO AT LEAST
BRIEFLY SHIFT NORTH CLOSER TO LAKE MICHIGAN WHICH WOULD BRING WIND
SPEEDS BACK UP IN EXCESS OF 25 KT ON OR AROUND TUESDAY.

LATE DAY VISIBLE SATELLITE IMAGERY ON TUESDAY APPEARED TO SHOW
SOME OPEN WATER IMMEDIATELY ALONG THE ILLINOIS SHORE SINCE THE ICE
HAD BEEN PUSHED OFFSHORE WITH SOUTHWEST WINDS DURING TUESDAY.
HOWEVER...FOR THE MOST PART ICE APPEARED TO BE 3 MILES OR SO OUT
TO ABOUT 20 MILES FROM THE ILLINOIS AND WISCONSIN SHORES...AND
OUT TO AROUND 30 TO 35 MILES FROM THE INDIANA SHORE. IT APPEARED
MUCH THICKER ALONG THE INDIANA SHORE.

MTF

&&

.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 251736
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1136 AM CST WED FEB 25 2015

.UPDATE...

1104 AM...LATE MORNING UPDATE...A LARGE AREA OF LIGHT SNOW
EXTENDS FROM EASTERN NEBRASKA THROUGH MUCH OF IOWA LATE THIS
MORNING WITH SNOW NOW BEING REPORTED AS FAR EAST AS DBQ. EXPECT
SNOW TO ARRIVE A BIT EARLIER THAN PREVIOUSLY EXPECTED AND BUMPED
POPS UP SOME... MAINLY ACROSS THE NORTHWEST CWA. BUT WILL NEED TO
MONITOR TRENDS AS THIS COULD STILL BE A LITTLE SLOW. THE HEAVIEST
OF THE SNOW IS EXPECTED TO FALL ACROSS EASTERN IOWA INTO WEST
CENTRAL IL INCLUDING PARTS OF THE SOUTHWEST CWA AND ITS POSSIBLE
AMOUNTS COULD REACH ADVISORY CRITERIA IN THE FAR SOUTHWEST
COUNTIES...BUT NOT PLANNING ANY HEADLINES AT THIS TIME. CURRENT
AMOUNTS LOOK OK FOR THE REST OF THE CWA AND WILL ISSUE AN SPS
SHORTLY.

OTHERWISE...TEMPERATURES HAVE WARMED INTO THE LOWER/MID 20S IN THE
CITY AND I-80 CORRIDOR TO THE UPPER 20S SOUTHERN AREAS AND HAVE
ADJUSTED TEMPS ACCORDINGLY. NOT EXPECTING TEMPS TO RISE MUCH
FURTHER WITH THE INCREASING CLOUDS AND SLOWLY STRENGTHENING
NORTHEAST WINDS. CMS

&&

.SHORT TERM...
345 AM CST

THROUGH THURSDAY...

SHORT TERM FOCUS IS ON THE INCOMING CLIPPER SYSTEM THAT WILL FRESHEN
THE SNOWPACK ACROSS MUCH OF THE AREA LATER TODAY AND TONIGHT.

FAIRLY QUIET ACROSS THE AREA EARLY THIS MORNING WITH A WIDE RANGE IN
TEMPERATURES AS SURFACE HIGH PRESSURE HOLDS AND MOSTLY CLEAR SKIES
HAS ALLOWED SOME OUTLYING AREAS TO DIP INTO THE SINGLE
DIGITS...WHILE MOST LOCATIONS SIT IN THE TEENS. NORTHERLY FLOW IS IN
PLACE THIS MORNING AS OUR FORMER SURFACE TROUGH MOVES EASTWARD...AND
STRONG HIGH PRESSURE PUSHES SOUTH JUST EAST OF THE NORTHERN CANADIAN
ROCKIES. CLOUD COVER IS QUICKLY SPREADING EAST THROUGH IOWA AND WILL
THICKEN UP FAIRLY QUICKLY ACROSS THE AREA NOT LONG AFTER DAYBREAK
FROM WEST TO EAST. THEREFORE EXPECT TEMPERATURES TO GENERALLY HOLD
IN THE TEENS THIS MORNING...BEFORE SOME INCREASE THIS AFTERNOON
AHEAD OF THE CLIPPER.

THE SURFACE LOW LOOKS TO TRACK SOUTHEAST TODAY FROM THE CENTRAL
PLAINS TO THE MID MISSOURI VALLEY THIS EVENING. THERE IS A FAIRLY
STOUT BAROCLINIC ZONE ON THE NORTH SIDE OF THE LOW DUE TO THE ARCTIC
HIGH WHICH WILL CONTINUE SOUTHWARD AS WELL INTO THE NORTHERN PLAINS.
THE STRONGEST FRONOTOGENESIS WITH THIS SYSTEM WILL REMAIN TO OUR
SOUTH AND WEST...BUT LATER THIS AFTERNOON AND EVENING. THERE IS
ENOUGH FRONTOGENETICAL FORCING ACCOMPANYING THE SOMEWHAT MODEST
HEIGHT FALLS...PRODUCING MODEST OMEGA BUT THROUGH A VERY DEEP
DENDRITIC GROWTH ZONE THAT WE SHOULD SEE SOME PRETTY STEADY THOUGH
LIGHTER SNOW BEGINNING IN THE ROCKFORD AREA MID AFTERNOON AND
SPREADING THROUGH THE REST OF THE AREA TONIGHT. THE STRONGER FORCING
SHIFTS EVEN FARTHER SOUTH TONIGHT...BUT THE UPPER WAVE IS STILL
PASSING THROUGH SO SOME CONTINUED LIGHT SNOW...BUT FAR NW AREA COULD
SEE THINGS TAPER.

THEN WE SHIFT GEARS QUICKLY TO LAKE EFFECT SNOW POTENTIAL ON
THURSDAY. LAKE INDUCED EQUILIBRIUM LEVELS ARE STILL A LITTLE LOWER
OVERNIGHT SO CURRENT THINKING IS ANY LAKE ENHANCEMENT OVERNIGHT
WOULD INITIALLY BE MINOR...THAT AND THE WIND FIELD IS A BIT STRONGER
AND THERE ARE SOME UNCERTAINTIES WITH LAKE ICE COVERAGE AS TO HOW
MUCH HEAT/MOISTURE FLUX WILL BE TRANSFERRED TO THE LOWER ATMOSPHERE.
BUT THERE STILL LOOK TO BE SOME LAKE EFFECT SHOWERS AFTER MIDNIGHT.
THERE IS A STILL A MODEST SIGNAL FOR LAKE EFFECT SNOW ON THURSDAY IN
NE ILLINOIS...BUT THE LOW LEVEL FLOW DOES LOOK PROGRESSIVE ENOUGH
THAT ANY BANDING THAT FORMS WOULD NOT IMPACT ONE AREA TOO LONG AND
WINDS STILL LOOK TO REMAIN UP LIMITING STRONG CONVERGENCE IN ANY ONE
SPOT. WITH ALL THAT SAID...SNOWFALL TOTALS THROUGH THURSDAY LOOK TO
BE HIGHEST IN THE SW WHERE 2-3 INCHES IS POSSIBLE...WITH 1-2 INCHES
ACROSS MUCH OF THE REMAINDER OF THE AREA...LIGHTEST ALONG THE
WISCONSIN BORDER...AND POSSIBLY HIGHER NEAR THE LAKE.

KMD

&&

.LONG TERM...
345 AM CST

THURSDAY NIGHT THROUGH TUESDAY...

SOME LAKE EFFECT SNOW SHOWERS ARE LIKELY TO PERSIST INTO NORTHWEST
INDIANA ON THURSDAY NIGHT ALTHOUGH SO WILL THE SAME CONCERNS IN THE
SHORT TERM ON HOW ORGANIZED OR NOT THESE WILL BE AND HOW MUCH THE
ICE WILL HAMPER THE HEAT FLUX AND INSTABILITY GENERATION. THERE
ARE INDICATIONS THAT AS THE WIND FIELD EASES SOME AND THE FLOW
BECOMES MORE NORTH-TO-SOUTH ORIENTED...THUS PARALLEL TO THE OPEN
WATER AREA...THAT A MORE ORGANIZED BAND MAY TEMPORARILY BE FAVORED
OVER THE LAKE AND POSSIBLY REACHING LAKE AND PORTER COUNTIES
THURSDAY EVENING.

A FITTING END TO THIS NEAR TO POSSIBLY RECORD COLD FEBRUARY IS IN
STORE WITH TEMPERATURES FLIRTING WITH DAILY RECORD TERRITORY /SEE
MORE IN THE CLIMO DISCUSSION BELOW/. MODEL GUIDANCE IS IN AGREEMENT
WITH 925MB TEMPERATURES OF -15 TO -19 THURSDAY NIGHT INTO FRIDAY
THEN MODIFYING GRADUALLY ON SATURDAY. THESE ARE IN THE LOWEST ONE
PERCENTILE OF 925MB REANALYSIS FROM THE PAST 35 YEARS FOR THE AREA
DURING THIS TIME OF YEAR. WITH SOME LIGHT FRESH SNOW COVER THIS
THE AIR MASS SHOULD REMAIN CHILLED WITH BELOW ZERO READINGS AT
NIGHT APART FROM DOWNTOWN CHICAGO. AS THE HIGH MOVES OVER THE
AREA ON FRIDAY NIGHT...LOW TEMPERATURES COULD END UP EVEN COOLER
AND COOLER THAN FORECAST...WITH SOME NEGATIVE DOUBLE DIGITS
CONCEIVABLE IN THE USUAL COOL SPOTS. WITH SUN EXPECTED DURING THE
DAY FRIDAY AND AT LEAST EARLY SATURDAY...WOULD EXPECT THE LOWER
ALBEDO AREAS SUCH AS THE CITY OF CHICAGO TO MODERATE A LITTLE MORE
THAN OUTLYING LOCALES...SOMETHING COMMON AS WE GET INTO THIS TIME
OF YEAR WITH INCREASING SUN ANGLE YET SNOW COVER STILL PRESENT.

AN UPPER LEVEL CIRCULATION...IF NOT CLOSED THEN NEAR IT...LOOKS
TO DEVELOP ACROSS THE SOUTHWEST U.S. BY SATURDAY NIGHT INTO SUNDAY.
BUILDING HEIGHTS AND RETURN MOISTURE AND ISENTROPIC ASCENT ARE
FORECAST OVER THE MIDDLE OF THE COUNTRY DURING THAT PERIOD. A
COUPLE OF SHORT WAVES EMANATING FROM THE PARENT LOW ARE FORECAST
BY THE 02.25 EC AND GFS TO RIDE OVER THE AREA WHILE THE GEM
MAINLY KEEPS THESE SOUTH. LEANING MORE BY THE FORMER GLOBAL
MODELS...SNOW WOULD BE LIKELY WITHIN A 15-24 HOUR WINDOW OF
SATURDAY NIGHT INTO/THROUGH SUNDAY. MIXING RATIOS OF AROUND 2.5 TO
3 G/KG ARE FORECAST TO RETURN ON GENERALLY CONTINUOUS ISENTROPIC
ASCENT. A BIT TOUGH TO TELL IF ANY MESOSCALE ENHANCEMENT WOULD BE
PRESENT WITHOUT MUCH OF A 850/700MB WAVE FORECAST...BUT AT THIS
POINT LOOKS LIKE THIS COULD BE A SEVERAL-INCHES-OF-SNOW-TYPE EVENT
OVER THAT PERIOD. THE GEM...AS WELL AS A SOUTHWARD TREND IN THE
25.00 GEFS...REMIND US THAT THE SOUTHWARD SOLUTION IS STILL
CERTAINLY A POSSIBILITY YET...AS SOME ADDED ADDITIONAL LIGHT SNOW
COVER THE NEXT 24-36 HOURS AND THE STRONG HIGH IN PLACE STILL ON
FRIDAY NIGHT MAY KEEP THE MID-LEVEL BAROCLINICITY A LITTLE FURTHER
SOUTH AND THUS THE SNOW THIS WEEKEND. SO OVERALL MEDIUM-HIGH
CONFIDENCE IN THE NORTHERN AND CENTRAL IL/IN REGION SEEING SOME
SNOW SATURDAY NIGHT AND SUNDAY...BUT LOW ON EXACTLY HOW FAR NORTH.

EARLY NEXT WEEK THE CONFIDENCE REALLY PLUMMETS AS ENERGY CONTINUES
TO BUCKLE INTO THE SOUTHWEST U.S. AND ROUND THE WEST-SOUTHWEST
FLOW INTO THE MIDDLE OF THE COUNTRY. THERE COULD BE SOME
MODERATION IN TEMPERATURES JUST GIVEN THIS PATTERN...BUT HOW MUCH
AND IF THE PATTERN WILL BE AS ACTIVE AS WHAT SOME OF THE LONG
RANGE MODELS INDICATE IS JUST TOO DIFFICULT TO SAY AT THIS TIME.

MTF

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

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

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB


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

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR WILL LAST.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...V