FXUS63 KLSX 021752
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1152 AM CST WED DEC 2 2009

.UPDATE...
/1036 AM CST WED DEC 2 2009/
GOING FORECAST PRETTY MUCH ON TRACK...ESPECIALLY IN REGARDS TO
CHANGE-OVER OF PRECIP FROM RAIN TO SNOW. HOWEVER...WE HAVE GOTTEN
VERY SPORATIC REPORTS OF SLEET WITH THE HIGHER REFLECTIVITIES IN S
MO...SO HAVE ADDED SOME IP IN AREAS FROM SAR WWD...WHERE UVV WILL BE
MAXIMIZED. CERTAINLY POSSIBLE THAT HIS LIFT WILL COOL THE COLUMN
AND CAUSE THE CHANGEOVER FROM RAIN TO SNOW TO OCCUR IN THE E
OZARKS PERHAPS AS FAST AS IT OCRS IN MID MO. AGAIN...THIS TREND
IS REFLECTED QUITE NICELY IN GOING FORECAST WITH SLIGHTLY HIGHER
ACCUMULATIONS IN THESE AREAS...BUT AREA WILL NEED TO BE WATCHED
DURING THE AFTERNOON.

TRUETT

&&

.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 AM CST WED DEC 2 2009/

FOR THE 18Z TAFS...MAIN PRECIP SHIELD ASSOCIATED WITH UPPER LOW IS
TRYING TO SPIN ITS WAY NW INTO STL AREA. DRY LO LEVEL AIR IS
CURRENTLY HOLDING PRECIP AT BAY...WHICH CAN BE SEEN BY VERY SLOW
NWD PROGRESSION OF THE ECHO MASS ON THE .5 ELEVATION SLICE FROM
KLSX 88D. HOWEVER...CERTAINLY THINK THAT STRONG LIFT FORECAST INTO
AREA THIS AFTERNOON WILL OVERCOME THE DRY AIR ALLOWING PRECIP TO
REACH BOTH STL AND SUS BY AROUND 20Z...WITH THE STEADY PRECIP
CAUSING CIGS/VSBYS TO LOWER TO MVFR AND OCCASIONALLY IFR AS WE
HEAD INTO THE LATE AFTERNOON AND EARLY EVENING HOURS. IF THE RUC
SOUNDINGS ARE TO BE BELIEVED ONSET OF SNOW MAY OCCUR IN STL AND
SUS LATER THAN 00Z...BUT WONDERING IF THE STRONG UVV AND
EVAPORATIVE COOLING WHICH WILL OCCUR AS LO LEVELS SATURATE MAY COOL
COLUMN AND ALLOW CHANGEOVER TO OCCUR A BIT EARLIER THAN SUGGESTED
BY FORECAST SOUNDINGS. IN ANY EVENT...IT CERTAINLY APPEARS THAT
THE BULK OF THE PRECIPITATION WILL BE WINDING DOWN BY THE TIME THE
LOW LEVELS COOL ENOUGH TO PRODUCE ALL SNOW...SO "WORST" WINTER
CONDITIONS ARE REFLECTED AS A MIX OF RA/SN. FURTHER W...MVFR CIGS
RAPIDLY DEVELOPED BETWEEN 15Z AND 16Z ACROSS MUCH OF W MO AND S
CNTRL IA...AND CIGS OF 15-25 KFT SHOULD IMPACT BOTH COU AND UIN
THROUGHOUT THE AFTERNOON...WITH THESE LOWER CLOUDS SLOWLY LIFTING
AND SCATTERING OUT DURING THE EVENING. CAN'T RULE OUT A BIT OF
VERY LIGHT PRECIPITATION AT COU AND UIN...BUT FOR NOW HAVE KEPT
TAFS FOR THESE LOCATIONS DRY DUE TO LACK OF SFC REPORTS OF S- AND
RELATIVELY LIGHT RETURNS ON REGIONAL RADAR MOSIAC.

TRUETT

&&

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

$$

WFO LSX