FXUS63 KLOT 091832
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1232 PM CST WED DEC 9 2009

.DISCUSSION...
1035 AM CST

NO CHANGES TO GOING HEADLINES AT THIS TIME.

SOME LIGHT SNOW WILL PERSIST OVER THE NEXT FEW HOURS AS A PAIR OF
MID/UPPER LEVEL DISTURBANCES...ONE MOVING THROUGH EAST CENTRAL
ILLINOIS...AND ANOTHER WRAPPING BACK WESTWARD ACROSS NORTHWEST
ILLINOIS WILL CONTINUE TO PROVIDE SOME FORCING. SOME EVIDENCE OF
A TROWAL SIGNATURE WRAPPING INTO NORTHERN ILLINOIS AT PRESENT
TIME...ALTHOUGH INSPECTION OF SHORT TERM NAM/WRF CROSS SECTIONS
SUGGEST GREATER INSTABILITY ASSOCIATED WITH THIS TROWAL IS PRESENT
IN A LAYER WELL ABOVE STRONGER UVM. FRONTOGENETICAL FORCING ALSO
RATHER WEAK...SO TAKING ABOVE FACTORS INTO ACCOUNT AND CONSIDERING
UPPER LEVEL LOW WILL BE TRANSLATING EAST BY MID AFTERNOON...DO
THINK IDEA OF AROUND AN INCH OF ADDITIONAL ACCUMULATION IS
REASONABLE. THE MAIN CONCERN FOR THIS AFTERNOON WILL BE THE STRONG
GUSTY WEST WINDS. SFC PRESSURE FALLS STILL NOTED OVER SFC LOW
CENTER ACROSS WEST CENTRAL LOWER MICHIGAN SO EXPECTING SOME
ADDITIONAL SLIGHT DEEPENING OF SFC LOW BEFORE IT BEGINS TO FILL.
STRONGEST ISALLOBARIC GRADIENT WITH THE DEPARTING LOW APPEARS TO
BE POSITIONED FROM EASTERN IOWA INTO CENTRAL ILLINOIS AT 16Z WHERE
GUSTS TO AROUND 40 TO 45 MPH HAVE BEEN COMMON. BASED ON EXPECTED
PROGRESSION OF THIS STRONGEST ISALLOBARIC CONTRIBUTION...WOULD
EXPECT PERIOD OF STRONGEST WINDS FOR FORECAST AREA TO BE IN THE
18Z-22Z TIME FRAME AND WILL HAVE TO MONITOR BLOWING SNOW RESPONSE
TO THESE WINDS. SPOTTER REPORTS INDICATE SNOW IS FAIRLY WELL
SETTLED AND PACKED SO SOME QUESTION AS TO HOW LOW VSBYS WILL DROP
BUT WITH SOME ADDITIONAL FRESH NEW SNOW THIS MORNING STILL HAVE
CONCERN FOR GROUND BLIZZARD CONDITIONS ACROSS NORTHWESTERN
PORTIONS OF CWA. AT THIS TIME WILL MAINTAIN WINTER STORM WARNING
HEADLINES DUE TO POSSIBILITY OF REDUCED VISIBILITIES IN BLOWING
SNOW. WEAKENING/DEPARTING SFC PRESSURE RISES THIS EVENING STILL
SEEM TO SUGGEST THAT ENDING TIMES OF WINTER STORM WARNING/WINTER
WEATHER ADV/WIND ADVISORY STILL REASONABLE...ALTHOUGH GUSTY WINDS
AND AREAS OF BLOWING SNOW SHOULD PERSIST INTO TONIGHT.

MARSILI

&&

.AVIATION...

1800 UTC TAFS...LAST REMNANT BANDS OF HEAVIER SNOW WILL MOVE THRU
EARLY IN TAF PERIOD WITH BLOWING SNOW THE MAIN ISSUE. REDUCED VSBY
AS HIGH WINDS TO 40 KTS KICKS UP DEPOSITED SNOW AMNTS FROM THIS
MRNGS SNOW BANDS. EARLIER AND HEAVIER SNOWS PROBABLY PACKED WELL AND
EVEN CRUSTED OVER AND NOT EXPECTED TO ADD TO VSBY REDUCTION. CIGS
ARE OTHER ISSUE. SHUD DROP TO IFR WITH THESE LINGERING BANDS OF
SNOW...OTHERWISE LOW MVFR FROM 1K TO 2K UNTIL TONIGHT. THEN CIGS
LIFTING TO VFR AROUND MDNGT TNGT AS COLD AND WET WRAPAROUND PULLS
AWAY AND HIGH PRESSURE PUSHES IN ANTICYCLONIC FLOW. CIGS LIKELY TO
START BREAKING UP BY MRNG WITH WINDS DROPPING OFF TO 25 KTS. SO
QUITE CONFIDENT OF VFR CONDS FOR THURSDAY DESPITE A CHILLY START
IN THE SINGLE DIGITS.

RLB

&&

.MARINE...
1230 PM CST

DEEP SURFACE LOW OVER LAKE HURON THIS EVENING SHOULD KICK OUT FOR
SRN QUEBEC BY MRNG BUT STILL MAINTAIN GALE FORCE WINDS OVER THE
LAKE. EVEN WITH LOW TRACKING NE TO NRN QUEBEC FRIDAY...PRESSURE
GRADIENT ACROSS THE LAKES STILL QUITE STRONG AS HEFTY HIGH
PRESSURE PATTERN FROM THE NRN ROCKIES AND PLAINS BUILDS SE ACROSS
THE MS VLY TO THE MID ATLANTIC COAST THRU THAT PERIOD. FINALLY GET
SOME RELAXATION OF WINDS LATE FRIDAY NIGHT INTO SATURDAY AS SFC
LOW PULLS OFF THE EAST COAST OF CANADA...AND THE WESTERN PORTION
OF RIDGING ACROSS THE OHIO VLY BUILDS NORTHWEST OVER THE LAKES.
WINDS OVER LAKE GENERALLY WEST TO NW AT GALES FORCE THRU FRIDAY
BUT FINALLY BACKING TO SW LATE FRI NGT AND SAT.

RLB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011 UNTIL 6 PM WEDNESDAY.

     WINTER WEATHER ADVISORY...ILZ012-ILZ013-ILZ014-ILZ019-ILZ020 
     UNTIL 6 PM WEDNESDAY.

     WIND ADVISORY...ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 
     6 PM WEDNESDAY.

IN...WIND ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 6 PM 
     WEDNESDAY.

LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...9 PM WEDNESDAY TO 1 AM 
     SATURDAY.

     STORM WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 PM WEDNESDAY.

     GALE WARNING...NEARSHORE WATERS UNTIL 4 
     AM FRIDAY.

&&

$$