FXUS63 KLSX 150457
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1057 PM CST MON DEC 14 2009

.DISCUSSION...
/335 PM CST MON DEC 14 2009/

ARCTIC AIRMASS IS CONTINUING ITS SURGE INTO THE MISSISSIPPI VALLEY 
THIS AFTERNOON...WITH THE LEADING EDGE JUST MOVING INTO THE FAR SE 
COUNTIES OF OUR CWA AT THIS TIME.  IT'S NOT CAUSING THE FASTEST TEMP 
DROP WE'VE EVER SEEN BUT IT'S CERTAINLY RESPECTABLE...AND AS OF
330 PM THE TEMP AT THE FORECAST OFFICE HAD DROPPED 14 DEGREES FROM
THE HIGH OF 54 RECORDED AT 1230 PM. THE CHANGE OVER THE NORTHERN
OZARKS HAS BEEN MORE DRAMATIC AS THEY WERE CLIPPED BY THE WARM
AIR JUST AHEAD OF THE FRONT EARLIER THIS MORING AND ARE NOW DEEPER
INTO THE COLD AIR. TEMP AT JEF HAS TUMBLED 24 DEGREES SINCE ITS
MID MORNING HIGH OF 54.  

THE EFFECT OF THIS AIRMASS OVER THE REGION IS PRIMARY FORECAST 
CONCERN IN THE SHORT TERM.  THE GREATEST IMPACT OF THIS COLD AIR 
WILL BE TONIGHT AND TUESDAY...WITH A SLOW MODERATION IN TEMPS 
OCCURRING DURING THE WED-THU TIME FRAME AS UA FLOW BECOMES 
QUASI-ZONAL.  THE LATEST 12Z GUIDANCE SUGGESTS THAT TEMP TRENDS IN 
GOING FORECAST ARE PRETTY MUCH ON THE MARK WITH THE
SPECIFICS...HOWEVER DID DROP TEMPS OVER THE SE HALF OF THE FA ON
WEDNESDAY NIGHT AS THIS AREA WILL REMAIN UNDER THE RADIATIONAL
INFLUENCES OF THE RETREATING SURFACE RIDGE.

ANY THREAT OF PRECIPITATION OVER THE NEXT 3 DAYS SHOULD BE ALMOST 
NON-EXISTENT. STILL SOME CONCERN THAT WE COULD SEE SOME VERY SPOTTY 
DRIZZLE OR FLURRIES TONIGHT AS THE COLDER AIR LIFTS AND SQUEEZES THE 
MOISTURE OUT OF THE RELATIVELY WARM AND MOIST LO LVL AIR LOCATED 
AHEAD OF THE FRONT...HOWEVER WITH THE DEARTH OF REPORTS OF ANY 
PRECIP OVER NW MO WILL GO WITH A DRY FORECAST FOR THIS EVENING.    
AFTER TONIGHT AIRMASS THROUGHOUT THE MID MISS VALLEY WILL BE VERY 
DRY AND DYANMICS WILL BE CONFINED TO AREAS FROM THE N PLAINS TO THE 
UPPER GREAT LAKES.

MODELS ARE STILL FORECASTING A SHORTWAVE IN THE WESTERLIES TO PUSH 
AND DIG INTO THE CENTRAL U.S. LATE THIS WEEK AND WILL CONTINUE LOW 
CHANCE POPS FRIDAY NIGHT AND INTO SATURDAY WITH THIS FEATURE.   
FORECAST SOUNDINGS DURING THIS TIME STRONGLY SUGGEST ANY PRECIP THAT 
DOES OCCCUR WILL BE ALL SNOW...BUT WITH VERY LIMITED MOISTURE IT 
APPEARS THAT QPF WILL BE QUITE LOW.

THIS SHORTWAVE WILL ALSO USHER IN THE NEXT ROUND OF COLD AIR...WHICH 
IS FORECAST TO STRENGHTEN OVER THE AREA WITH TIME.  YESTERDAYS 
MEDIUM RANGE MODELS WERE ALL OVER THE PLACE WITH THEIR TRENDS 
HEADING INTO NEXT WEEK...BUT TODAYS GUIDANCE IS IN MUCH BETTER 
AGREEMENT IN THE LARGE SCALE TRENDS.  THEY ALL DEPICT FORMATION OF 
AN ELONGATED UPPER LEVEL VORTEX FROM THE UPPER LAKES INTO THE 
CANADIAN MARITIMES AND NE U.S. FROM LATE SATURDAY INTO MONDAY WITH 
SEVERAL CIRCULATION CENTERS WOBBLING AROUND THIS VORTEX. THIS 
PATTERN IS ONE THAT CLEARLY MEANS BELOW NORMAL TEMPERATURES FOR OUR 
REGION....PRIMARY QUESTION IS HOW COLD TO GO.  THE ECMWF...WHICH 
TAKES ONE OF THE UPPER LOWS AND DROPS IN ALL THE WAY SOUTH IN THE 
OHIO VALLEY AND CENTRAL APPALACIANS...LOOKS QUITE ODD FROM A 
CLIMATOLOGICAL POINT OF VIEW...SO THINK IT IS PROBABLY TOO COLD.  
PREFER THE TRENDS OF THE OPERATIONAL GFS WHICH KEEPS THE CIRCULATION 
CENTERS MORE ANCHORED OVER THE GREAT LAKES REGIONS.  EVEN FAVORING 
THE SOLUTIONS WHICH ARE LESS AGRESSIVE WITH THE COLD AIR...HAVE 
TRENDED TEMPS FROM SUN-MON WELL BELOW THE 12Z MEX NUMBERS...WITH A 
STRONG LEAN TOWARD THE COLDEST MEMBERS OF THE 00Z MOS ENSEMBLES.

TRUETT

&&

.AVIATION...
/1057 PM CST MON DEC 14 2009/

FOR THE 06Z TAFS...
SKIES WILL CONTINUE TO CLEAR OUT OVERNIGHT AS SFC HIGH BUILDS INTO 
THE REGION. CIGS AT STL/SUS SHUD BECOME VFR WITHIN A COUPLE OF 
HOURS. WINDS WILL GRADUALLY VEER AND BECOME LIGHT AND VRB TUES EVE 
UNDER MOSTLY CLEAR SKIES.

TILLY

&&

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

$$

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