FXUS63 KLOT 270003
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
603 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...
600 PM CST

0000 UTC TAFS...ANOTHER TRICKY FORECAST FOR THE NEXT FEW HOURS.

THE CENTER OF THE UPPER LOW HAS SHIFTED INTO WISCONSIN. SATELLITE
IMAGERY CONTINUES TO INDICATE A SERIES OF MID LEVEL IMPULSES
ROTATING AROUND THE LOW. LATEST IMAGERY SHOWS A STRONG IMPULSE
EXITING NERN IL AND MOVING OVER SRN LAKE MICHIGAN. THIS WILL
SIGNAL THE END OF THE HEAVIEST SNOWFALL. HOWEVER...RADAR IMAGERY
SHOWS SMALL POCKETS OF HEAVIER PCPN REMAINING OVER NERN IL...WHICH
SHOULD IMPACT ORD/MDW. RADAR IMAGERY ALSO INDICATES A SHARP BACK
EDGE TO THE GENERAL SNOW AREA. AT ISSUANCE TIME...THE BACK EDGE
MOVING THROUGH RFD AT 00Z AND IS TIMED TO MOVE THROUGH ORD/MDW BY
ATOUND 03Z. AFTER 03Z...SNOW SHOULD BECOME LIGHT...WITH VIS
REMAINING IN MVFR RANGES FOR A FEW MORE HOURS. FINALLY VIS SHOULD
GO VFR BY 06Z. CEILINGS SHOULD GENERALLY REMAIN MVFR OVER NERN
IL...BUT NWRN/NCNTRL IL...INCLUDING RFD...WILL SEE A PERIOD OF VFR
SKIES AS A CLEAR SLOT MOVES OVERHEAD. PER LATEST SATELLITE
TRENDS...DO NOT EXPECT THE CLEARING SLOT TO REACH ORD/MDW/DPA AREA.

MODEL GUIDANCE INDICATES ANOTHER STRONG IMPULSE MOVING AROUND THE
SRN PERIPHERY OF THE UPPER LOW TOMORROW. THE TRACK OF THIS IMPULSE
IS EXPECTED TO TAKE THE STRONGEST FORCING TO THE SOUTH OF THE
TERMINALS...SO DO NOT EXPECT ANOTHER ROUND OF HEAVY SNOW.
HOWEVER...THE FAR NORTHERN EXTENT OF THE INFLUENCE OF THIS IMPULSE
SHOULD REACH FAR ENOUGH NORTH SO THAT ORD/MDW/DPA/GYY SHOULD SEE
IFR CONDITIONS DURG THE LATE MORNING AND EARLY AFTERNOON HOURS.
RFD SHOULD ESCAPE THE HEAVIEST SNOW WITH THIS IMPULSE...WITH ONLY
MVFR CIGS/VIS LIKELY.  

THE SYSTEM RESPONSIBLE FOR THE SNOW SHOULD FINALLY EJECT TO THE
EAST TOMORROW EVENING...BRINGING AN END TO THE SNOW.

KREIN

&&

.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.
&&

$$