Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 202105
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
305 PM CST THU NOV 20 2014

.SHORT TERM...

TONIGHT THROUGH SATURDAY...

305 PM...MAIN FORECAST CONCERN AND CHALLENGE REMAINS LIGHT
FREEZING RAIN POTENTIAL FRIDAY NIGHT INTO EARLY SATURDAY MORNING.

ANOTHER BLUSTERY DAY WITH WINDS GUSTING 30-35 MPH WITH TEMPS
REACHING THE UPPER 20S TO LOWER 30S ACROSS SOUTHERN AREAS. CLEAR
SKIES WILL CONTINUE INTO TONIGHT AS A RIDGE OF HIGH PRESSURE
BUILDS ACROSS THE REGION ALLOWING WINDS TO BECOME LIGHT AND
VARIABLE OVERNIGHT. ONE LAST NIGHT OF VERY COLD TEMPS...UNTIL
NEXT WEEK...WITH LOW TEMPS TANKING TO THE SINGLE DIGITS NORTH TO
PERHAPS LOWER TEENS ACROSS THE SOUTH.

AS THE RIDGE SHIFTS EAST FRIDAY...FLOW TURNS LIGHT SOUTHERLY AND
WITH QUITE A BIT OF SUN EXPECTED THRU EARLY AFTERNOON ALONG WITH
WARMING TEMPS ALOFT...SHOULD AT LEAST BE ABLE TO REACH SAME TEMPS
AS TODAY AND PERHAPS A FEW DEGREES WARMER.

WARMER AIR CONTINUES TO SPREAD NORTH FRIDAY NIGHT AS WEAK LIFT
BEGINS TO SQUEEZE OUT SOME LIGHT PRECIPITATION. AIR TEMPERATURES
WILL INITIALLY REMAIN BELOW FREEZING AS PRECIPITATION BEGINS TO
FALL. DRY LOW LEVELS MAY SUPPORT SOME LIGHT SLEET AT ONSET...BUT
APPEARS THE MAIN PRECIP TYPE WILL BE LIGHT FREEZING RAIN AS A VERY
DEEP WARM LAYER DEVELOPS OVERNIGHT. QPF AMOUNTS HAVE GENERALLY
RANGED FROM A FEW HUNDREDTHS ACROSS THE NORTHERN CWA TO PERHAPS AS
MUCH AS A TENTH OF AN INCH ACROSS THE SOUTHEAST CWA INTO NORTHWEST
INDIANA. SO A PERIOD OF LIGHT FREEZING RAIN APPEARS LIKELY.

MAIN QUESTION WILL THEN BE HOW LONG DOES IT PERSIST. GROUND
SURFACES HAVE BEEN SUB FREEZING FOR OVER A WEEK WITH HIGH TEMPS
MAYBE REACHING NEAR THE FREEZING MARK FRIDAY. THUS IT WILL TAKE
SOME AMOUNT OF TIME FOR AIR TEMPERATURES ABOVE FREEZING TO WARM
THESE COLDER SURFACES AND END FREEZING RAIN POTENTIAL. CONFIDENCE
ON THIS TIMING IS FAIRLY LOW. HOURLY TEMP TRENDS HAVE TEMPS INTO
THE MID 30S ACROSS THE SOUTHERN CWA AND TO AROUND FREEZING
NORTHERN AREAS BY 12Z SATURDAY. THESE TEMPS ARE IN LINE AND
PERHAPS A TAD COOLER THAN THE GFS/ECMWF. TEMPS CONTINUE TO
STEADILY RISE THROUGH THE MID/UPPER 30S SATURDAY MORNING...WITH
PRECIPITATION BECOMING ALL LIQUID. ANY AMOUNT OF LIGHT FREEZING
RAIN OR FREEZING DRIZZLE WILL BECOME HAZARDOUS ON UNTREATED
SURFACES AND PLAN TO ISSUE AN SPS THIS AFTERNOON TO HIGHLIGHT THE
THREAT.

TEMPERATURES CONTINUE TO WARM INTO THE 40S SATURDAY WITH A CHANCE
OF LIGHT RAIN OR PERHAPS SOME DRIZZLE. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH FRIDAY...

305 PM...MAIN FORECAST CONCERNS ARE HEAVY RAIN SUNDAY/SUNDAY
EVENING AND THEN ANOTHER PROLONGED PERIOD OF COLDER/BELOW NORMAL
TEMPS NEXT WEEK.

NOT MUCH CHANGE IN TEMPS IS EXPECTED SATURDAY NIGHT AS LOW LEVEL
MOISTURE STREAMS NORTH. TEMPS MAY HOLD STEADY IN THE LOWER TO MID
40S. EXTENT OF FOG IS STILL A BIT UNCERTAIN BUT POTENTIAL FOR FOG
CONTINUES HIGH ENOUGH TO MAINTAIN IN THE FORECAST WITH AT LEAST
THE CHANCE OF SOME DENSE FOG.

LOW PRESSURE WILL DEVELOP OVER THE SOUTHERN PLAINS SATURDAY NIGHT
AND MOVE NORTH ACROSS THE AREA SUNDAY AFTERNOON OR SUNDAY EVENING.
WHILE THE LOW IS STILL EXPECTED TO DEEPEN TO AS LOW AS 976MB OVER
THE NORTHERN LAKES MONDAY...IT MAY DEEPEN A BIT SLOWER AND ITS
OVERALL TRACK COULD BE A BIT SLOWER AND A TAD FURTHER EAST...FROM
EASTERN IL TO SOUTHERN MICHIGAN SUNDAY NIGHT. NET AFFECT OF THIS
WOULD BE TO BRING THE AXIS OF HEAVY RAIN RIGHT OVER THE CWA FROM
SUNDAY AFTERNOON INTO SUNDAY EVENING. PRECIPITABLE WATER VALUES
STILL PROGGED INTO THE 1.0 TO 1.2 INCH RANGE DURING THIS TIME
PERIOD. STORM TOTAL RAINFALL OF 1 TO 2 INCHES STILL LOOKS POSSIBLE
BUT NOT ENOUGH CERTAINTY TO TRY TO PIN DOWN A PARTICULAR AREA OF
THE CWA...IT MAY END UP BEING MUCH OF THE AREA.

TRACK OF THE LOW WILL ALSO LIKELY RESULT IN A RATHER SHARP TEMP
GRADIENT...PERHAPS ONLY LOW/MID 40S WESTERN AREAS AND LOW/MID 50S
FAR EASTERN AREAS. A COLD FRONT WILL MOVE ACROSS THE AREA SUNDAY
NIGHT BRINGING COLD AIR BACK TO THE AREA WITH FALLING TEMPS
THROUGH THE 30S MONDAY. LINGERING PRECIP WILL CHANGE FROM LIGHT
RAIN TO LIGHT SNOW WITH SNOW SHOWERS/FLURRIES POSSIBLE MONDAY INTO
MONDAY NIGHT. STILL LOOKS QUITE BREEZY EARLY NEXT WEEK WITH
SPECIFICS DEPENDING ON THE TRACK/STRENGTH/TIMING OF THE LOW.

CONFIDENCE REGARDING MID/LATE NEXT WEEK IS LOW. A WEAKER CLIPPER
LIKE SYSTEM IS SHOWN BY THE GFS ON WEDNESDAY AND THE ECMWF ON
THURSDAY WITH A STRONG COLD FRONT MOVING ACROSS THE AREA AND
ANOTHER PUNCH OF VERY COLD AIR. WHILE THEY ARE SIMILAR THE TIMING
DIFFERENCES ARE LARGE ENOUGH WITH LITTLE CONTINUITY FROM THE 00Z
ECMWF...TO NOT MAKE ANY BIG CHANGES AT THIS TIME. CMS

&&

.AVIATION...

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

* GUSTY WEST WINDS THROUGH THIS AFTN WITH MAX GUSTS 25-30 KT.

KMD

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

SOME MVFR CUMULUS TRYING TO FORM THIS AFTERNOON BUT IT WILL HAVE A
HARD TIME GETTING MORE COVERAGE THAN SCATTERED. HIGH PRESSURE WILL
BE MOVING OVERHEAD TONIGHT...THUS SKIES CLEAR TONIGHT WITH WINDS
EASING FROM WEST TO EAST. WIND DIRECTION TRENDS TO SOUTH TOMORROW...PEAKING
AROUND 10 KT OR SO...POSSIBLY WITH A SLIGHT SE COMPONENT. EXPECT
AN INCREASE IN HIGH CLOUDS THROUGH THE DAY.

KMD

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

* HIGH CONFIDENCE IN ALL ELEMENTS

KMD

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

FRIDAY NIGHT...SCHC WINTRY MIX BECOMING A CHC OF FREEZING RAIN
OVERNIGHT. IFR CIGS LIKELY. SOUTH WINDS ARND 10 KT.

SATURDAY...CHC -RA/FREEZING RAIN BECOMING RAIN AND FOG OVERNIGHT.
IFR LIKELY. SOUTH-SOUTHWEST WINDS 10-15 KT.

SUNDAY...RAIN. IFR LIKELY. GUSTY SOUTHEAST WINDS.

MONDAY...CHC -RASN BCMG CHC -SN. MVFR CIGS PSBL. STRONG SOUTHWEST
WINDS WITH GUSTS ARND 30 KT PSBL.

TUESDAY...SCHC -SN DURING THE DAY. MVFR CIGS PSBL. GUSTY WEST
WINDS.

WEDNESDAY...VFR. WEST WINDS BCMG SOUTHWEST.

JEE

&&

.MARINE...
200 PM CST

LOW PRESSURE OVER SOUTHCENTRAL QUEBEC WILL CONTINUE TO SLIDE EAST.
AN ELONGATED RIDGE OF HIGH PRESSURE STRETCHES FROM THE NORTHERN
PLAINS SOUTHEAST THROUGH THE TENNESSEE VALLEY...AND WILL SLOWLY MOVE
EAST TOWARDS LAKE MICHIGAN TONIGHT. HIGH PRESSURE WILL BRING MUCH
LIGHTER WINDS TO LAKE MICHIGAN BY FRIDAY MORNING...HOWEVER HIGH
PRESSURE IS EXPECTED TO CONTINUE TO SLIDE EAST TOWARDS THE MIDDLE
ATLANTIC REGION BY LATE FRIDAY NIGHT. AS HIGH PRESSURE DEPARTS LAKE
MICHIGAN...WINDS WILL TURN SOUTHWEST TO SOUTH FRIDAY NIGHT. AN AREA
OF LOW PRESSURE WILL SLIDE EAST ACROSS MANITOBA TOWARDS JAMES
BAY...WITH A TIGHTENING GRADIENT EXPECTED TO DEVELOP BY LATE FRIDAY
NIGHT ACROSS CENTRAL/NORTHERN LAKE MICHIGAN. HAVE HELD IN PLACE THE
GALE WATCH...HOWEVER THIS MAY NEED TO BE UPGRADED TO A GALE WARNING.
THE MAIN CONCERN IS THAT WITH MUCH WARMER AIR POISED TO ARRIVE
FRIDAY NGT...THAT THIS MAY CREATE LESS MIXING TO THE SURFACE OF THE
HIGHER WIND GUSTS. GUIDANCE SUGGESTS GALES MAY BE BETWEEN 34-37KT SO
ALONG THE MARGINAL LINES.

DURING THE DAY SATURDAY THE GRADIENT WILL DIMINISH ONCE AGAIN AND
TURN SOUTHEASTERLY...HOWEVER THIS WILL ONLY BE TEMPORARY AS A MORE
POTENT LOW PRESSURE SYSTEM IS POISED TO SLIDE SOUTHEAST FROM CENTRAL
CANADA SATURDAY NIGHT. A WEAKER LOW PRESSURE SYSTEM WILL DEVELOP
ACROSS THE SOUTHERN PLAINS EARLY SUNDAY...THEN QUICKLY LIFT NORTH
TOWARDS LAKE MICHIGAN. GUIDANCE DIFFERS ON THE EXACT STRENGTH AND
PATH OF THIS LOW...BUT MODELS INDICATE THE LOW WILL DEEPEN TO AROUND
975 MB/28.8 INCHES AT THE NORTH END OF THE LAKE MONDAY AFTERNOON.
EXPECTING SOUTHEAST WINDS TO INCREASE TO AT LEAST 30 KT THROUGH
SUNDAY EVENING AND THEN BECOME SOUTHWEST BEHIND THE LOW. GALES ARE
EXPECTED BY LATE SUNDAY NIGHT AND DEPENDING ON THE PATH AND STRENGTH
OF THE LOW...STORM FORCE WINDS MAY BE INCLUDED IN FUTURE FORECASTS.
GUIDANCE INDICATED A BRIEF PERIOD OF HIGH END GALES OVER THE
NORTHERN END OF THE LAKE MONDAY AFTERNOON.  THE LOW MOVES OVER
QUEBEC TUESDAY WITH WEST WINDS DIMINISHING TUESDAY MORNING.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 AM FRIDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM FRIDAY.

     GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ868-LMZ870...6 PM FRIDAY TO 9 AM SATURDAY.

&&

$$

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