FXUS63 KLSX 021011
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
411 AM CST WED DEC 2 2009

.DISCUSSION...
/357 AM CST WED DEC 2 2009/

CDFNT EXTENDS FROM WI SW THRU NWRN MO TO THE TX PNHDL.  THIS CDFNT 
WILL BE MOVING SEWD THRU THE CWA TDA AS THE MID-UPPER LEVEL TROF
CURRENTLY OVER THE NRN ROCKYS AND NRN PLAINS DEEPENS OVER THE NRN
PLAINS. AT THE SAME TIME RAIN WAS SPREADING NWD THRU OK AND AR N
AND NE OF A MID LEVEL LOW OVER TX AND ITS ASSOCIATED SFC LOW OVER
LA WITH AN INVERTED SFC TROF EXTENDING NWD THRU WRN MS. THE GFS
MODEL HAS FINALLY COME IN LINE WITH THE OTHER MODELS REGARDING THE
TRACK OF THE SRN UPPER/SFC LOW AND ITS PRECIPITATION SHIELD. THE
CLOSED MID LEVEL LOW WILL TRACK NEWD THRU AR TDA OPENING UP AS IT
MOVES INTO WRN TN BY 00Z THU. THE SFC LOW WILL MOVE N-NEWD THRU MS
AND WRN TN AND INTO KY BY 00Z THU. THE MAJORITY OF THE
PRECIPITATION WILL FALL ACROSS THE SERN HALF OF THE CWA TDA AND
THIS EVNG...MAINLY FROM STL S AND E...LEFT OF THE PATH OF THE
500MB/850 MB/SFC LOW TRACK. AS COLD AIR CONTINUES TO FILTER SEWD
THRU THE CWA BEHIND THE CDFNT AND THE NEWD ADVANCING SFC LOW THE
RAIN WILL CHANGE OVER TO SNOW DURING THE LATE AFTN AND EVNG
HOURS...GENERALLY FROM NW TO SE WITH TIME. LOOKING AT THE LATEST
MODEL FORECAST SOUNDINGS THIS CHANGE OVER WILL BE A LITTLE SLOWER
THAN PREVIOUSLY FORECAST WHICH WILL LESSEN THE PERIOD OF SNOWFALL
AND HENCE LOWER SNOW ACCUMULATIONS. ALSO THE FORECAST TRACK OF
THE LOW HAS SHIFTED A LITTLE FURTHER SE WHICH WILL SHIFT THE
BETTER SNOW ACCUMULATION FURTHER SE. USED A CORRIDOR 90 NM LEFT OF
THE PREFERED TRACK OF THE 850 MB LOW TO GIVE AN ESTIMATE OF WHERE
THE BEST SNOW ACCUMULATION MAY OCCUR. THIS WOULD GENERALLY EXTEND
FROM ELLINGTON AND FARMINGTON MISSOURI NE THROUGH SPARTA AND SALEM
ILLINOIS. A MORE BROAD AREA OF LIGHTER SNOW MAY OCCUR FURTHER NW
WHERE THE MODELS DEPICT STRONG UPPER LEVEL DIVERGENCE OVER THE
CWA FROM LATE MRNG TO EVNG DUE TO COUPLING OF THE NRN AND SRN
STREAM ULJ STREAKS. DUE TO THE WARM GROUND TEMPERATURES AND SFC
TEMPERATURES ABOVE FREEZING THE SNOWFALL WILL NOT LIKELY
ACCUMULATE MUCH EXCEPT DURING THE BRIEF PERIOD WHEN IT IS
OCCURRING AT MODERATE TO HEAVY INTENSITY. ACCUMULATIONS SHOULD BE
GENERALLY LESS THAN ONE INCH ALTHOUGH THERE COULD BE ISOLATED
AREAS WITH 1-2 INCHES MAINLY ON GRASSY AREAS RATHER THAN ON ROADS.
THIS ACCUMULATING SNOW SHOULD MELT/SUBLIMATE SHORTLY AFTER IT
STOPS FALLING. THE POTENTIAL OF ACCUMULATING SNOW SHOULD END LATE
TGT AS THE UPPER/SFC LOW PULLS WELL E OF THE CWA WITH ONLY
LINGERING FLURRIES AS STRONG NWLY WINDS CONTINUE TO BRING COLDER
AIR SEWD INTO THE CWA. VERY COLD TEMPERATURES ARE EXPECTED THU
THRU FRI NGT DUE TO A PROLONGED PERIOD OF LOW LEVEL CAA WITH 850
MB TEMPERATURES CONTINUING TO FALL...EVENTUALLY DROPPING TO -12
TO -13 DEGREES C ACROSS MOST OF THE CWA BY 18Z FRI. LOW LEVEL
CLOUDINESS ALONG WITH FLURRIES IS EXPECTED ON THU OVER THE NRN AND
NERN PORTION OF THE CWA DUE TO THE LARGE MID-UPPER LEVEL TROF
MOVING SLOWLY EWD THRU THE NRN PLAINS INTO THE GREAT LAKES REGION.
IT APPEARS THAT ANY ACCUMULATING SNOW ON THU WILL REMAIN N OF THE
CWA CLOSER TO THE COLD CORE OF THE MID-UPPER LEVEL LOW AND THE
SHRTWVS ROTATING AROUND IT.

GKS

&&

.AVIATION...
/1139 PM CST TUE DEC 1 2009/

FOR THE 06Z TAFS...
00Z NAM AND GFS ARE COMING INTO BETTER AGREEMENT WITH RESPECT TO
SNOW FOR WEDNESDAY. IT LOOKS LIKE THE PRECIP WILL MOSTLY STAY AWAY
FROM CENTRAL AND NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS AND
CONCENTRATE ALONG AND EAST OF THE I-44/I-55 CORRIDORS. FORECAST
SOUNDINGS ARE HINTING THAT THE PRECIP WILL STAY MOSTLY RAIN IN
EAST CENTRAL MISSOURI...WITH RAIN CHANGING TO SNOW IN THE LATE
AFTERNOON/EARLY EVENING FURTHER SOUTH IN THE HIGHER ELEVATIONS OF
THE OZARKS NEAR KFAM. KSTL/KSUS COULD STILL SEE A FEW FLAKES AND IFR
VSBYS DURING THE EVENING BEFORE THE PRECIP ENDS...BUT I'M NOT SURE
THERE WILL BE MUCH OPERATIONAL IMPACT BEYOND IFR VSBYS AND WET
RUNWAYS. OF POTENTIALLY MORE IMPACT WILL BE GUSTY NORTHWEST WINDS
WHICH WILL RAMP UP ACROSS THE AREA IN THE AFTERNOON AS THE SURFACE
LOW ASSOCIATED WITH THIS SYSTEM MOVES UP OUT OF THE GULF INTO THE
TENNESSEE VALLEY. COULD SEE GUSTS AS HIGH AS 25-30KTS BEFORE WINDS
SUBSIDE A BIT IN THE EVENING.

UNTIL WEDNESDAY AFTERNOON'S ACTION...I EXPECT VFR CONDITIONS AND
LIGHT SOUTH-SOUTHEAST FLOW ACROSS THE BI-STATE AREA. WINDS WILL
BECOME NORTH-NORTHWESTERLY AS A COLD FRONT MOVES THROUGH THE
REGION EARLY WEDNESDAY MORNING.

CARNEY

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

$$

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