FXUS63 KLOT 260516
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1116 PM CST WED NOV 25 2009

.DISCUSSION...
738 PM CST

UPPER LOW/STRONG VORT MAX EMBEDDED WITHIN BROADER LARGE SCALE
TROUGH CONTINUES TO TRACK EAST-SOUTHEASTWARD ACROSS IA TOWARD
NORTHERN/CENTRAL ILLINOIS. COLDER CLOUD TOPS ASSOCIATED WITH WARM
CONVEYOR BELT ARE WRAPPING AROUND THE NORTH SIDE OF THE UPPER LOW
THIS EVENING WITH BEGINNINGS OF TROWAL (TROUGH OF WARM AIR ALOFT)/
DEFORMATION ZONE DEVELOPING. THE WARMER AIR WRAPPING AROUND THE
NORTH SIDE OF THIS SYSTEM THAT IS SUPPORTING THE PRECIPITATION IS
ALSO RESPONSIBLE FOR SLOWING THE COOLING OF THE COLUMN AND KEEPING
TEMPS WARM ENOUGH FOR PRIMARILY RAIN WITHIN THE DEFORMATION
PRECIP THUS FAR...WITH STRONGEST COLD AIR ADVECTION TAKING PLACE TO
THE SOUTH OF THE PRECIP AXIS.

AS VORT MAX TRACKS EAST ACROSS NORTHERN PORTIONS OF CENTRAL
ILLINOIS LOOK FOR SOMEWHAT OF A BREAK IN PRECIP OR AT LEAST A
TAPERING TO DRIZZLE ACROSS SOUTHERN AND POSSIBLY EVEN CENTRAL
PORTIONS OF THE CWA LATER THIS EVENING INTO THE START OF THE
OVERNIGHT. BY LATER TONIGHT AS THE UPPER LOW CONTINUES EASTWARD
TROWAL WILL BEGIN TO WRAP MORE AROUND THE UPPER LOW AND INTO THE
REGION OF STRONG COLD AIR ADVECTION. THAT...PLUS THE TIME OF
DAY...WOULD BOTH FAVOR AN INCREASE IN COVERAGE OF SNOW LATE
TONIGHT INTO EARLY THURSDAY MORNING. 

AS PREVIOUS DISCUSSION ALLUDED TO...LOW LEVEL THERMAL PROFILES
WILL BE MARGINAL FOR SNOW AND LIKELY TOO WARM FOR ANY APPRECIABLE
ACCUMULATIONS TO OCCUR. WHILE CHANCES OF ANY ACCUMULATING SNOWFALL
APPEAR SMALL...IT DOES APPEAR AS THOUGH THERE WILL PROBABLY BE A
PERIOD OF SOMEWHAT STEADIER PRECIPITATION THAT WILL PROBABLY FALL
AS MOSTLY SNOW AS DEFORMATION BAND BECOMES MORE N-S ORIENTED AND
MOVES ACROSS THE AREA VERY LATE TONIGHT AND THURSDAY MORNING. 

ONLY VERY MINOR COSMETIC TWEAKS HAVE BEEN MADE TO GRIDS
TONIGHT...HOWEVER HAVE TRENDED WX GRIDS A BIT MORE TOWARD SNOW FOR
THURSDAY MORNING. UPDATED GRIDS/TEXT PRODUCTS WILL BE ISSUED
SHORTLY.

IZZI

&&

.AVIATION...
1115 PM CST

0600 UTC TAFS...SATELLITE ALONG WITH VAD AND PROFILER WINDS
POSITION MID/UPPER LOW OVER FAR NE IL AT 04Z. LATEST MODEL RUNS
HAVE IT MOVING ENE ACROSS FAR SOUTHERN LAKE MI TO FAR SW LOWER MI
OVERNIGHT. -RA TO BEGIN TO MIX WITH -SN AS FREEZING LEVEL
CONTINUES TO DROP TO AROUND 1500 FT AGL OVERNIGHT. SIGNIFICANT SN
FALLING ACROSS SOUTHERN WI AND FAR NW AND N CENTRAL IL IN
DEFORMATION ZONE. WITH SYSTEM MOVING ENE DO NOT ANTICIPATE THIS TO
REACH LOCAL TERMINALS. -RASN MIX TO PERSIST THRU MIDDAY THU AS 
SYSTEM CONTINUES MOVING SLOWLY JUST N OF DUE E.

BESIDES AREA OF IFR CONDITIONS IN SOUTHERN WI INTO NW IL...MVFR
CEILINGS AND UNRESTRICTED VSBY PREVALENT SO HAVE KEPT MVFR IN
TAFORS WITH ONLY TEMPO HI END IFR DURING OVERNIGHT INTO THU
MORNING.

DEEPENING AND STRENGTHENING UNIDIRECTIONAL NW FLOW SPREADS ACROSS
THE AREA AS MID LEVEL CIRCULATION MOVES FROM OVERHEAD AND EXPECT
WINDS TO GUST 25-30KT BY MID MORNING. SIGNIFICANT DRYING FORECAST
TO OCCUR DURING THE LATER AFTERNOON SO OVC TO BECOME BKN.

TRS

&&

.MARINE...
1146 AM CST

A LOW PRESSURE LOCATED NEAR TRAVERSE CITY MICHIGAN WILL LIFT
NORTHEAST ACROSS THE SOO THIS EVENING...WHILE TRAILING A TROUGH
SOUTHWARD ACROSS INDIANA. THIS LOW IS THEN FORECAST TO DRIFT
ACROSS NORTHERN LAKE HURON ON THURSDAY AS A REINFORCING PUSH OF 
COLD AIR IS DRAWN EASTWARD ACROSS THE SOUTHERN GREAT LAKES BY
THURSDAY MORNING. AS THE LOW SLOWLY MOVES EASTWARD ACROSS
ONTARIO...A PERIOD OF GUSTY NORTHWEST WINDS WILL DEVELOP BEHIND
THURSDAY AND THURSDAY NIGHT. WINDS WILL DIMINISH ON FRIDAY AS HIGH
PRESSURE RIDGING SPREADS ACROSS THE WESTERN GREAT LAKES.

MERZLOCK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743...10 AM 
     THURSDAY TO 4 AM FRIDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...NOON THURSDAY TO 4 PM 
     FRIDAY.

&&

$$