FXUS63 KLOT 110452
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1052 PM CST THU DEC 10 2009

.DISCUSSION...

800 PM CST

FOR EVENING UPDATE...GOING FORECAST IN PRETTY GOOD SHAPE EARLY
THIS EVENING. MADE A FEW MINOR TWEAKS TO SKY COVER AND HOURLY TEMP
TRENDS MAINLY ACROSS THE FAR NORTHERN IL PORTION OF CWA.

LATE AFTERNOON/EVENING GOES 11-3.9 MICRON IR IMAGERY INDICATES 
PATCHY CLOUD COVER FROM SOUTHEAST MN/SOUTHERN WI TO FAR NORTHERN IL. 
THIS AREA OF CLOUD COVER ASSOCIATED WITH WEAK SHORT WAVE TROUGH 
NOTED IN 12/00Z RAOB/PROFILER ANALYSIS ALONG CYCLONIC SHEAR SIDE OF 
STRONG POLAR JET ACROSS MIDWEST. FAIRLY TIGHT LOW LEVEL THERMAL ZONE 
FROM NORTHWEST IA TO CENTRAL/NORTHERN IL...WITH SOME DEGREE OF 
BAROCLINICITY/WARM ADVECTION NOTED WITH BACKED WINDS IN SFC-850 HPA 
LAYER NOTED ACROSS EASTERN IA/SOUTHERN WI/NORTHERN IL. SHORT RANGE 
GUIDANCE IN DECENT AGREEMENT IN SHEARING/DAMPING THIS WAVE TO THE 
EAST/SOUTHEAST ACROSS WI/IL OVERNIGHT...WITH MOST FOCUSED FORCING 
THIS EVENING. SOME SFC OBSERVATIONS REPORTING SOME FLURRIES WITH 
THIS DISTURBANCE ACROSS SOUTHERN MN/WESTERN WI...THOUGH APPEARS 
BETTER THREAT FOR ANY LIGHT PRECIP WILL REMAIN NORTH OF IL/WI 
BORDER. MAINLY JUST SOME PATCHY BROKEN CLOUD COVER EXPECTED ACROSS 
FAR NORTHERN IL AT TIMES MAINLY DURING EVENING HOURS.

WITH ARRIVAL OF PATCHY CLOUDS AND WEAK LOW LEVEL WARM ADVECTION...
HAVE NOTED TEMPS ACTUALLY RISING A DEGREE OR TWO IN SOME LOCATIONS 
ACROSS NORTHWEST/NORTH CENTRAL IL LAST COUPLE OF HOURS AS 
RADIATIONAL COOLING WAS IMPEDED. HAVE MODIFIED HOURLY TEMPS TO SHOW 
A SLOWER FALL OVERNIGHT...BASED ON 12 KM WRF SFC TEMPS. ESSENTIALLY 
HAVE KEPT MINS THE SAME HOWEVER...AS PERIOD OF CLEAR SKIES AND 
DECOUPLED WINDS ESPECIALLY OVER DEEPER SNOW COVER SHOULD STILL 
SUPPORT GOING COLD TEMPS.

RATZER

&&

.AVIATION...

06Z TAFS...MAIN FORECAST CONCERNS ARE WIND SPEEDS OVERNIGHT AND
POSSIBLE VFR CIGS FRIDAY.

AS HIGH PRESSURE DRIFTS EAST ACROSS THE OHIO VALLEY AND DEEP LOW
PRESSURE SLOWLY MOVES NORTHEAST ACROSS QUEBEC...THE GRADIENT HAS
REMAINED TIGHT ENOUGH FOR SOME GUSTS ACROSS NORTHEAST IL THIS
EVENING. GUIDANCE WOULD SUGGEST GUSTS SHOULD RELAX OVER THE NEXT
SEVERAL HRS. WILL HOLD ONTO GUSTS TO 18KTS AT ORD/MDW FOR A FEW
HRS BUT OVERALL EXPECT PREVAILING WINDS OF 10-15KTS. WINDS ALSO
HAVE TURN BACK MORE WESTERLY AND WILL STAY WEST/SOUTHWEST THRU
MIDDAY FRIDAY...BEFORE TURNING MORE SOUTHERLY FRIDAY EVENING.

EARLIER 4-6KFT CLOUDS HAVE QUICKLY MOVED EAST WITH ANOTHER PATCH
ACROSS SOUTHERN MN/NORTHERN IA SHIFTING EAST. AS WARM AIR
ADVECTION BEGINS OVERNIGHT INTO FRIDAY MORNING...EXPECT SCT/BKN
MID CLOUDS TO DEVELOP THAT SHOULD DISSIPATE AND LIFT NORTHEAST
THRU THE AFTERNOON. CMS

&&

.MARINE...
1227 PM CST

A DEEP LOW PRESSURE OVER WESTERN QUEBEC...IN COMBINATION WITH A
SPRAWLING HIGH PRESSURE AREA OVER THE LOWER MISSISSIPPI VALLEY
WILL CONTINUE TO PRODUCE STRONG WEST WINDS ACROSS THE GREAT LAKES
THROUGH THIS EVENING. AS THE LOW CENTER TRACK OFF TOWARD LABRADOR
TONIGHT AND FRIDAY...WINDS WILL SLOWLY ABATE AND BACK SLIGHTLY
INTO THE SOUTHWEST. THE HIGH PRESSURE CENTER WILL SHIFT EASTWARD
TO THE MID ATLANTIC REGION BY LATE FRIDAY...AS A RIDGE EXTENDS TO
THE NORTHWEST...ACROSS THE WESTERN GREAT LAKES. WITH THE PASSAGE
OF THIS RIDGE AXIS FRIDAY EVENING...WINDS WILL DIMINISH MORE
NOTICEABLY...AND BACK INTO THE SOUTH.

MERZLOCK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL MIDNIGHT SATURDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL MIDNIGHT 
     SATURDAY.

&&

$$