FXUS63 KLOT 262149
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
349 PM CST SAT DEC 26 2009

.DISCUSSION...
349 PM CST

RUNNING WAY BEHIND DUE TO ONGOING SNOW STORM SO TODAY'S DISCUSSION
WILL BE VERY ABBREVIATED. 

SMALL SCALE VORT MAX PIVOTING AROUND MAIN CYCLONE IS MOVING INTO
EASTERN ILLINOIS AT THIS TIME...WITH HEAVIEST SNOW MOVING ACROSS
CWA AT THIS TIME. CONTINUE TO SEE EMBEDDED AREAS OF 30DBZ+ ECHOS
WITH HEAVIEST SNOW BAND...WHICH HAS BEEN CORRELATING WITH ROUGHLY
1-2 INCH PER HOUR SNOWFALL RATES. PLAN TO LEAVE LATEST HEADLINES
GOING AS IS BUT WILL BE BUMPING UP MAX SNOWFALL TOTALS TO JUST
OVER A FOOT FOR WEST AND NORTHWEST SUBURBS. 

ANOTHER...HOPEFULLY LESS IMPRESSIVE...IMPULSIVE PIVOTS AROUND THE
UPPER LOW TOMORROW. APPEARS AS THOUGH TOMORROW'S VORT WILL TAKE A
MORE SOUTHERN TRACK. MUCH LIKE TODAY...FORECAST SOUNDINGS SUGGEST
VERY DEEP DENDRITIC GROWTH ZONE. MODEL QPF IS LIGHTER WITH
TOMORROW'S SYSTEM THAN IT WAS WITH TODAYS...THOUGH USING A 30:1
SNOW:LIQUID RATIO STILL YIELDS A COUPLE/FEW INCHES OF SNOW OVER
OUR SOUTHERN MOST CWA. 

ONLY OTHER REAL CHANGE TO GOING GRIDS WAS TO BACK OFF ON
TEMPERATURES SOMEWHAT DUE TO THE SNOW COVER. MIDNIGHT SHIFT WILL
HAVE MORE TIME TO LOOK AT AND ACCESS THINGS AND WILL PROBABLY
NEED TO CUT BACK ON TEMPS MORE.

IZZI

&&

.AVIATION...
1210 PM CST

1800 UTC TAFS...WATER VAPOR SATELLITE LOOP SHOWS MAIN UPPER
CIRCULATION CENTER OVER SOUTHERN WI WITH MULTIPLE IMPULSES
ROTATING AROUND IT. ONE SIGNIFICANT VORT MAX OVER THE IA-MO BORDER
IN UPPER TROF THE EXTENDS FROM THE MAIN LOW CENTER SW TO THE TX
PANHANDLE. AXIS OF THIS TROF TO SWING E OVER IL DURING THE
AFTERNOON SO EXPECT SN TO CONTINUE THRU THE AFTERNOON.
HOWEVER...AS SFC AND H8 LOWS OVER SE IA CONTINUE MOVING TO THE NE
AND REACH SE WI BY 00Z THE LOW LEVEL WAA AND UVV MOVES N AND NE OF
THE TERMINALS AND INTENSITY OF SN TO DIMINISH AS A RESULT. AFTER
TROF AXIS PASSES BY SHOULD SEE ONLY NON-ACCUMULATING -SN THIS EVE
AND INTO FIRST PART OF OVERNIGHT.

CURRENTLY CLR TO SCT CLOUDS ACROSS MUCH OF WI...SE MN AND IA WITH
MODELS TRYING TO BRING THIS DRYING FURTHER EASTWARD THIS EVENING
THO WITH UPPER LOW PROGGED TO MAKE A CYCLONIC LOOP OVER SOUTHERN
AND CENTRAL WI BETWEEN THIS AFTERNOON AND SUN MORNING AND EXPECT
AT LEAST BKN STRATOCU TO REMAIN ACROSS THE LOCAL TERMINALS INTO
THE NIGHT BEFORE STRONG PVA PUSHES SOUTHEASTWARD OVER NORTHERN IL DURING
THE EARLY MORNING HRS OF SUN. MODELS SHOW MID LEVELS SOMEWHAT
DRY AT THAT TIME...AND THEN TO HAVE DRIED MORE ACROSS THE
TERMINALS BY 15Z SUN AS UPPER TROF AXIS ONCE AGAIN MOVES ACROSS
NORTHERN IL. EXPECT PD OF LIGHTER ACCUMULATING SNOW AS PVA WILL
ONLY HAVE LIMITED MOISTURE IN MID LEVELS TO WORK WITH. 

TRS

&&

.MARINE...
232 PM CST

LOW PRESSURE IN EASTERN IA WILL MOVE NE ACROSS WI TONIGHT AND
CROSS NORTHERN LAKE MI SUN MORNING. AS THE LOW WEAKENS AND
REFORMS OVER JAMES BAY DURING SUNDAY A TROF WILL MOVE E ACROSS THE
LAKE. W TO NW WINDS BEHIND THE TROF WILL INCREASE SUN NIGHT AS HI
PRESSURE BUILDS OVER THE PLAINS. A STRONG COLD FRONT WILL THEN
DROP S DOWN THE LAKE ON MON WITH NW WINDS INCREASING TO 30-35 KT
BEFORE GRADUALLY DECREASING MON NIGHT AS THE CENTER OF HI PRES
MOVES E OVER THE UPPER MIDWEST AND MID MS VALLEY.

TRS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ005-ILZ006-ILZ011-ILZ012-ILZ013-ILZ014 
     UNTIL 9 PM SATURDAY.

     WINTER WEATHER ADVISORY...ILZ003-ILZ004-ILZ008-ILZ010-ILZ019-
     ILZ020-ILZ021-ILZ022 UNTIL 9 PM SATURDAY.

IN...WINTER WEATHER ADVISORY...INZ001 UNTIL 9 PM SATURDAY.

LM...NONE.
&&

$$