Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 282138
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
338 PM CST FRI NOV 28 2014

.SHORT TERM...
300 PM CST

THROUGH SUNDAY...

A TEMPERATURE ROLLER COASTER RIDE OVER THE NEXT FEW DAYS IS THE MAIN
FOCUS OF THE FORECAST.

TONIGHT AND SATURDAY...

W/V IMAGERY SHOWS THAT HIGHLY AMPLIFIED PATTERN THAT
RESULTED IN ALL THE COLD AIR THE PAST FEW WEEKS IS RAPIDLY BEING
REPLACED BY ZONAL MID AND UPPER FLOW. A VERY WARM AND DRY AIR MASS
OVER THE CENTRAL PLAINS THIS MORNING WILL RAPIDLY BE ADVECTED INTO
THE AREA TONIGHT INTO SATURDAY BY DECENT SOUTHWEST FLOW AT H85. IN
ADDITION...A SFC WARM FRONTAL FEATURE IS ALSO BEGINNING THE
PROCESS OF LIFTING WARMER AND MORE MOIST AIR NORTHWARD THIS
AFTERNOON...WHICH RESULTED IN PATCHY LOW CLOUD DEVELOPMENT FOR A
TIME. STILL SOME CONCERN FOR LIGHT QPF EARLY THIS EVENING IN THE
FAR NORTH...WHICH IF ANY COULD REACH THE GROUND WOULD LIKELY BE IN
THE FORM OF LIGHT SNOW OR PELLETS DUE TO WET BULB PROCESSES. THINK
THE FOCUS WILL BE JUST NORTH OF THE CWA SO HAVE REMOVED SLIGHT
POPS BUT WILL NEED TO MONITOR THIS. THE MODELS APPEAR TO BE
STRUGGLING GREATLY WITH AMOUNT OF SNOW COVER ON THE GROUND OVER
THE CWA...ESPECIALLY THE NAM AND RAP. EXPECTING THAT SKIES WILL
TREND TO PARTLY CLOUDY TONIGHT...WHICH DESPITE STEADY SOUTHERLY
WINDS...COULD SET THE STAGE FOR PATCHY GROUND FOG OVER STILL SNOW
COVERED AREAS. TEMPERATURES ARE EXPECTED TO REMAIN STEADY OR
SLOWLY RISE OVERNIGHT.

THE SNOW COVER/CLOUD COVER ISSUE COMES TO A HEAD ON SATURDAY.
LOOKING IN THE WARM SECTOR OF THE DEVELOPING HIGH PLAINS LOW
TODAY...THERE IS LITTLE IN THE WAY OF CLOUD COVER. HOWEVER...MANY
MODELS INSIST ON BREAKING OUT LOW CLOUDS/LOW LEVEL SATURATION. WITH
A +12 TO +15C AIR MASS AT 850 MB MOVING INTO THE AREA...SUSPECT THAT
MUCH OF THE GUIDANCE IS BIASED FAR TOO COLD TOMORROW. IT SEEMS THAT
THE CANADIAN GLOBAL AND REGIONAL MODELS...WHICH TYPICALLY DO BETTER
IN COOL SEASON WARM-UPS...HAVE A MUCH BETTER HANDLE ON LIKELY LACK
OF LOW LEVEL CLOUD COVER...WHICH CAN BE SEEN ON FORECAST SOUNDINGS.
HAVE BUMPED UP TEMPERATURES IN THE LOW-MID 50S AREA WIDE...EXCEPT
FOR NEAR 50 ALONG IMMEDIATE WI BORDER WHERE 2-4 INCHES OF SNOW DEPTH
WERE REPORTED TODAY. HAVE CONSERVATIVELY LOWERED SKY COVER
PERCENTAGE AS WELL...AS OTHER THAN SOME MID/HIGH CLOUDS...IT APPEARS
A DECENT AMOUNT OF SUN COULD BE IN STORE.

SATURDAY NIGHT AND SUNDAY...

A VERY MILD SATURDAY NIGHT WILL ALLOW FOR A ANOTHER WARM SUNDAY
FOR PARTS OF THE CWA. HOWEVER...THERE WILL BE AN ARCTIC FRONT
SURGING SOUTHWARD AHEAD OF EXPANSIVE AND STRONG HIGH PRESSURE OVER
THE NORTHERN PLAINS. TIMING OF THIS FRONT IS KEY AND NOW THINK IT
WILL BE INTO THE NORTHERN CWA BY LATE AM/MID DAY...CAPPING HIGHS
NEAR 40/LOW 40S THERE. FAR SOUTHERN CWA COULD CONCEIVABLY APPROACH
60 DEGREES GIVEN MORE TIME TO WARM UP AHEAD OF THE FRONT. UPPER
FORCING IS NOT IMPRESSIVE WITH THE FRONT BUT LOW LEVEL MOISTURE
CONVERGENCE AND DECENT LOW/MID F-GEN DUE TO QUICKLY TIGHTENING
THERMAL GRADIENT COULD BE ENOUGH FOR ISOLATED/WIDELY SCT`D RAIN
SHOWERS MAINLY IN AFTERNOON IN SOUTHEAST 1/3 OF CWA.

RC

&&

.LONG TERM...
249 PM CST

SUNDAY NIGHT THROUGH FRIDAY...

LOW LEVEL ARCTIC AIR MASS WILL QUICKLY SPILL SOUTHWARD SUNDAY NIGHT
AS UPPER TROUGH BRIEFLY DIGS ACROSS NORTHERN TIER AND STRONG HIGH
PRESSURE SPREADS SOUTHEAST. AIR MASS LOOKS FAIRLY DRY OVER THE
LAKE...BUT LAKE EFFECT PARAMETERS ARE MARGINALLY FAVORABLE FOR SOME
LAKE EFFECT SNOW SHOWERS SUNDAY NIGHT INTO MONDAY MORNING FOR THE
SOUTHEAST TIP OF THE LAKE. TEMPERATURES WILL TUMBLE INTO THE TEENS
AND 20S BY MONDAY MORNING...WITH CONTINUED COLD ADVECTION RESULTING
IN A WELL BELOW NORMAL START TO METEOROLOGICAL WINTER. HIGHS WILL
LIKELY  BE IN 20S CWA WIDE/IF NOT COLDER IN FAR NORTH...FOLLOWED BY
A COLD NIGHT MONDAY NIGHT AS 1040 MB+ HIGH PRESSURE MOVES OVERHEAD.
PATTERN WILL QUICKLY TURN ZONAL AGAIN BUT COLD AIR REMAINING JUST TO
NORTH SHOULD KEEP TEMPERATURES ON THE COOLER SIDE THROUGH MID WEEK.
BIG TIMING DIFFERENCES IN THE LATE WEEK TIMEFRAME WITH ECMWF AND
GFS/GEFS...AS ECMWF KEEPS DRY/COOL HIGH LOCKED IN TIL THURSDAY
MORNING...WHILE GFS BREAKS OUT PRECIP ALONG BAROCLINIC ZONE
WEDNESDAY NIGHT INTO THURSDAY. HAVE MAINTAINED LOW GUIDANCE BLEND
POPS BUT CONFIDENCE IS FAIRLY LOW IN TEMPS AND SENSIBLE WX
WEDS-THURSDAY...THOUGH A MILD PERIOD DOES LOOK TO BE IN THE CARDS
LATE NEXT WORK WEEK INTO THE WEEKEND.

RC

&&

.AVIATION...

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

* MVFR CIGS OF 1500-2200 FT THROUGH AT 00Z-01Z WITH A LOW CHANCE
  OF LINGERING LONGER.

* SOUTH-SOUTHEAST WINDS GUSTING 15-20 KT THROUGH 00Z.

* LOW CHANCE FOR MVFR CIGS TO LINGER THIS EVENING.

MDB/MTF


//DISCUSSION...UPDATED 20Z...

LATEST ANALYSIS SHOWS A CORRIDOR OF MVFR CIGS DEVELOPING ON THE
LEADING EDGE OF LOW LEVEL WARM AIR AND EVEN A SUBTLE SURFACE WARM
FRONT FROM KSFY TO KIKK. WINDS MAKE A SUBTLE SHIFT TO DUE SOUTH
AND TEMPERATURES BOUNCE UP SEVERAL DEGREES BEHIND THIS BOUNDARY.
TRENDS SHOW THE SCT-BKN MVFR LIFTING NORTHEASTWARD SO HAVE ADDED
A TEMPO FOR BKN CIGS AROUND 020 FOR THE NEXT FEW HOURS. THE BAND
OF CLOUDS LOOKS TO BE FAIRLY NARROW AS SITES THAT WERE BKN HAVE
GONE SCT OR LESS SO IT MAY BE SHORT LIVED. WILL CONTINUE TO
MONITOR CIG TRENDS FOR THE EVENING WHICH ARE LESS CERTAIN.

FROM 18Z...

SOUTH TO SOUTH-SOUTHEAST WINDS HAVE BEGUN TO GUST TO ABOUT 20 KT
IN THE LAST HOUR OR TWO AND EXPECT THESE GUSTS TO CONTINUE THROUGH
THE AFTERNOON. THE DIRECTION SHOULD BECOME A BIT MORE SOUTHERLY
WITH TIME. THE MAIN QUESTION IS POTENTIAL FOR MVFR CIGS TO DEVELOP
EARLY THIS EVENING AND VSBY REDUCTION POTENTIAL OVERNIGHT.
GUIDANCE CONTINUES TO BACK PEDAL ON STRATUS DEVELOPMENT TO THE
WEST IN THE NEAR TERM AS NONE HAS DEVELOPED YET. WARMER AIR WILL
BEGIN TO PUSH INTO NORTHEASTWARD JUST ABOVE THE SURFACE INTO THE
EVENING SO IT IS POSSIBLE THAT SOME STRATUS COULD DEVELOP BUT
MOISTURE LOOKS LARGELY INSUFFICIENT. WILL INDICATE SCATTERED MVFR
CLOUDS FOR A TIME THIS EVENING BUT THIS MAY BE TOO PESSIMISTIC.
OTHERWISE MID CLOUDS WILL LOWER WITH THE PASSAGE OF AN UPPER WAVE.
THE PUSH OF WARM AIR DIMINISHES EARLY TONIGHT SO STRATUS WOULD
BECOME LESS LIKELY. WITH TEMPERATURES EXPECTED TO BE STEADY OR
EVEN WARM A FEW DEGREES TONIGHT...THE LACK OF A STRONG PUSH OF
MOISTURE OVERNIGHT AND STEADY SOUTH WINDS WIDESPREAD VSBY
REDUCTION IS NOT FAVORED THOUGH SOME PATCHY FOG COULD DEVELOP OVER
AREAS WITH BETTER SNOW PACK INCLUDING RFD. BREEZY SOUTH TO SOUTH-
SOUTHWEST WINDS WILL DEVELOP SATURDAY. WILL CONTINUE WITH A VFR
FORECAST WITH MID/HIGH CLOUD COVER.

MDB


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

* MEDIUM-HIGH IN CIGS AND WINDS.

MDB/MTF


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

SATURDAY NIGHT...MAINLY VFR CONDS.

SUNDAY...MAINLY VFR. POSSIBLE LGT RAIN IN THE MORNING.

MONDAY...VFR.

TUESDAY...SLIGHT CHANCE OF LGT SNOW EARLY WITH PATCHY MVFR CIGS.
OTHERWISE VFR.

WEDNESDAY...VFR.

THURSDAY...MAINLY VFR. PATCHY LIGHT RAIN OR SNOW WITH PATCHY MVFR
CIGS.

BEACHLER

&&

.MARINE...
123 PM CST

SOUTHERLY WINDS WILL REMAIN ELEVATED IN THE 20 TO 30 KT RANGE
THROUGH SATURDAY NIGHT AS AN AREA OF LOW PRESSURE TRACKS
NORTHEASTWARD FROM THE DAKOTAS TO NEAR JAMES BAY. THIS LOW WILL
DRIVE A COLD FRONT SOUTHWARD ACROSS LAKE MICHIGAN DURING THE DAY ON
SUNDAY. MUCH COLDER AIR AND STRONG NORTHERLY WINDS WILL SET UP IN
THE WAKE OF THIS FRONT AS A STOUT 30.71+ INCH HIGH BUILDS OVER THE
PLAINS AND UPPER MIDWEST. THIS SHOULD RESULT IN 30 KT WINDS LATER
SUNDAY INTO MONDAY...THOUGH A PERIOD OF GALE FORCE WINDS SUNDAY
NIGHT AS THE HEART OF THE COLD AIRMASS SPILLS OVER THE LAKE.

THE SURFACE HIGH WILL SHIFT EASTWARD OVER LAKE MICHIGAN BY AROUND
MONDAY EVENING...LEADING TO A PERIOD OF ABATING WINDS. HOWEVER...AS
THIS HIGH SHIFTS EAST OF THE LAKE...IT APPEARS THAT WINDS WILL
INCREASE OUT OF THE SOUTH AGAIN BY TUESDAY AS IT APPEARS ANOTHER
DECENT STORM SYSTEM WILL TRACK NORTHEASTWARD INTO SOUTHERN CANADA.
THIS COULD RESULT IN ANOTHER PERIOD OF GALE OR NEAR GALE FORCE
SOUTHERLY WINDS...ESPECIALLY ACROSS NORTHERN LAKE MICHIGAN.

KJB

&&

.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




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.