Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 210906
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
306 AM CST FRI NOV 21 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 09Z...

* INCREASING SOUTHERLY WINDS...POSSIBLE CROSSWIND ISSUES THIS
  AFTERNOON.

* FREEZING RAIN LIKELY OVERNIGHT INTO EARLY SATURDAY.

LENNING

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

HIGH PRESSURE MOVING OVERHEAD WILL SUPPORT LIGHT WINDS OVERNIGHT.
WINDS TURN SOUTH DURING THE MORNING AND INCREASE IN SPEED DURING
THE AFTERNOON. THESE BREEZY SOUTH TO SSW WINDS PERSIST THROUGH
SATURDAY.

RAIN CHANCES INCREASE FRIDAY NIGHT AND TEMPERATURES WILL SLOWLY BE
ON THE RISE DURING FRIDAY NIGHT AS WELL. UNFORTUNATELY THE RAIN IS
LIKELY TO ARRIVE BEFORE TEMPERATURES CLIMB ABOVE FREEZING. THE PEAK
PERIOD OF CONCERN APPEARS TO BE IN THE PREDAWN HOURS MOSTLY BEFORE
TRAFFIC PICKS UP...BUT FREEZING RAIN COULD LINGER INTO THE FIRST
COUPLE HOURS OF THE MORNING RUSH.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE IN WIND...CEILING...AND VSBY TRENDS.

* MEDIUM TO HIGH CONFIDENCE IN FZRA TIMING AND CHANCES FRIDAY
  NIGHT.

LENNING

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

SATURDAY...CHANCE OF RAIN OR FREEZING RAIN EARLY...THEN RAIN
LIKELY WITH DENSE FOG POSSIBLE OVERNIGHT. MVFR CONDITIONS LIKELY
THROUGH MUCH OF THE DAY...IFR CONDITIONS LIKELY OVERNIGHT. SOUTH-
SOUTHWEST WINDS 10-15 KT.

SUNDAY...RAIN. HEAVY AT TIMES. 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/WX NIL DURING THE DAY. SCHC -SN OVERNIGHT. MVFR
CIGS/VIS PSBL. WEST TO SOUTHWEST WINDS 10 KT OR LESS.

KREIN

&&

.MARINE...
254 AM CST

IN THE TIGHT GRADIENT BETWEEN A DEEPENING LOW TO OUR NORTH AND
HIGH PRESSURE TO OUR SOUTHEAST...WINDS START WEST TODAY THEN
BACK SOUTH BY TONIGHT WHILE INCREASING TO STRONG GALES. THE NORTH
END OF THE LAKE LIKELY WILL SEE STRONGER AND EARLIER GALES THAN
THE SOUTH END...THUS THE TWO DIFFERENT START TIMES ON THE
WARNINGS. FOR SIMPLICITY THEY BOTH END AT THE SAME TIME SATURDAY
MORNING BUT LIKELY THE SOUTH WILL SEE GALES DIMINISH SOONER.

THE NEXT LOW PRESSURE SYSTEMS LIFT THROUGH ON MONDAY AND LIKELY
BRING ANOTHER PERIOD OF WEST GALES THAT AFTERNOON AND EVENING.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FREEZING RAIN ADVISORY...ILZ019-ILZ021-ILZ023-ILZ032-ILZ033-
     ILZ039...10 PM FRIDAY TO 6 AM SATURDAY.

     FREEZING RAIN ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ020-ILZ022...11 PM
     FRIDAY TO 9 AM SATURDAY.

IN...FREEZING RAIN ADVISORY...INZ001-INZ002...11 PM FRIDAY TO 9 AM
     SATURDAY.

     FREEZING RAIN ADVISORY...INZ010-INZ011-INZ019...10 PM FRIDAY TO
     6 AM SATURDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ872-
     LMZ874-LMZ876-LMZ878...9 PM FRIDAY TO 9 AM SATURDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ669-LMZ868-LMZ870...3 PM FRIDAY TO 9 AM SATURDAY.

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

     SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 AM FRIDAY.

&&

$$

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