FXUS63 KLSX 251053
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
453 AM CST FRI DEC 25 2009

.DISCUSSION...
/447 AM CST FRI DEC 25 2009/

SFC LOW CENTER OF THE CHRISTMAS STORM OF 2009 HAS PUSHED FROM THE 
OZARKS TO N OF IRK OVER THE PAST FEW HOURS...WITH A HUGE EWD
SURGE OF COLD AIR OCCURING IN THE WAKE OF THE LOW. TRYING TO
REFLECT RATHER CHAOTIC PRECIP TRENDS ACROSS THE CWA...AND SPECIFIC
TEMP TRENDS WITH SUCH AN EXTREME TEMP GRADIENT...ARE CERTAINLY THE
PRIMARY CONCERNS FOR EARLY TODAY.

VERY HEAVY DEF ZONE SNOWFALL BECAME ANCHORED JUST E OF KC METRO
AREA DURING THE PREDAWN HOURS.  ANIMATION OF REGIONAL RADAR LOOP
AS WELL AS IR PICS INDICATE THAT THIS BAND HAS WEAKENED A BIT AND
IS TRANSLATING ALMOST DUE N AS IT LIFTS/REFORMS OVER W IA.  LATEST
00Z AND 06Z MODEL GUIDANCE SUGGESTS THAT THIS TREND WILL CONTINUE
DURING THE MORNING...WITH PERHAPS THE E FRINGES JUST BRUSHING NE
AND CENTRAL MO.  BECAUSE OF THIS...IT CERTAINLY APPEARS THAT
SNOWFALL AMOUNTS WILL BE FAIRLY MINIMAL..PROBABLY NO MORE THAN AN
INCH FROM NEAR EDINA TO NEAR COU.

MEANWHILE...DRY SLOT WRAPPING ARND THE UPPER LOW OVER S MO 
HAS CAUSED A BIG DECREASE IN PRECIP ACROSS MUCH OF CNTRL AND
EASTERN MO DURING THE PREDAWN HOURS...ALTHOUGH SPOTTY PRECIP
SHOULD CONTINUE TO REFORM IN THIS AREA. THE LIGHT AND SPOTTY
NATURE OF THIS PRECIP SHOULD KEEP ANY SNOWFALL ACCUMULATIONS OVER
EASTERN MISSOURI AND SOUTHERN ILLINOIS VERY MINOR AS THE COLD AIR
SURGES EAST IN THE WAKE OF THE SFC LOW DURING THE MORNING.

CERTAINLY...ONCE THE COLD AIR ARRIVES TEMP TRENDS THROUGHOUT MOST OF 
THE DAY AND IN MOST AREAS WILL BE STEADILY DOWNHILL.  
HOWEVER...GIVEN WHAT SHOULD BE A VERY COLD START TO THE DAY OVER MID 
MO...WE MAY SEE TEMPS LEVEL OFF OR PERHAPS CLIMB A DEGREE OR TWO BY
MID AFTERNOON IN THIS AREA. USED A COMBO OF THE LATEST RUC 2M AND 06Z
NAM 2M TEMPS AS A FIRST APPROXIMATION FOR HOURLY TEMP TRENDS.

LATER THIS AFTERNOON AND TONIGHT...MODELS ARE IN GOOD AGREEMENT THAT 
AFOREMENTIONED UPPER LOW WILL LIFT INTO IOWA...AND SLOWLY MERGE WITH 
SECONDARY LOW CURRENTLY DROPPING THROUGH PLAINS.   THIS COMBINED 
SYSTEM WILL THEN TAKE UP RESIDENCE OVER THE UPPER MISSISSIPPI VALLEY 
FOR THE REMAINDER OF THE WEEKEND...WITH A SERIES OF SHORTWAVES 
FORCAST TO ROTATE AROUND THE LOW.  NET RESULT SHOULD MEAN A 
PROLONGED THREAT OF SNOW THROUGH SATURDAY AND INTO SATURDAY 
NIGHT...WITH THE BEST THREAT FOR SNOW ALG AND ESPECIALLY NORTH OF 
THE I-70 CORRIDOR WHERE DYNAMICS WILL BE THE STRONGEST.  THIS TREND 
IS ALREADY NICELY REFLECTED IN CURRENT FORECASTS SO NO MAJOR CHANGES 
REQUIRED.  

AFTER THE PASSAGE OF THE COLD FRONT EARLY THIS MORNING TEMPS WILL 
CERTAINLY BE BELOW NORMAL FOR THE REMAINDER OF THE WEEKEND.   
HOWEVER...DID NOT ALLOW TEMPS TO FALL TOO FAR FOR TONIGHT...AS 
MODELS ACTUALLY INDICATE A BIT OF WARM ADVECTION OCCURRING ON THE S 
SIDE OF THE OCCLUDING STORM SYSTEM.

TRUETT

&&

.AVIATION...
/1128 PM CST THU DEC 24 2009/

FOR THE 06Z TAFS...SURFACE LOW IS NOW JUST WEST OF KVIH AS OF 05Z 
AND WILL CONTINUE TO TRACK TO THE NORTH NORTHEAST EARLY THIS MORNING 
...INTO NORTHEAST MO THEN INTO IOWA. MILD TEMPERATURES PERSISTING 
OVER TAF SITES...SO PCPN ALL IN THE FORM OF RAIN FOR NOW. AS LOW 
PULLS NORTHWARD...PCPN WILL CHANGE OVER TO ALL SNOW BY 10Z AT 
KCOU...14Z AT KSUS/KSTL AND BY 15Z AT KUIN. AS FOR CIGS...WILL SEE 
MVFR CIGS OVER THE FIRST COUPLE OF HOURS...THEN THEY WILL SINK BACK 
DOWN TO IFR/LIFR TIL THIS AFTERNOON THEN LIFT TO MVFR. AS SURFACE 
LOW LIFTS NORTHWARD THROUGH CENTRAL MO IN THE NEXT COUPLE OF HOURS 
...GUSTY EAST WINDS TO GRADUALLY SHIFT TO THE SOUTHEAST THEN 
EVENTUALLY TO THE WEST TO SOUTHWEST BY LATE THIS MORNING...AND 
REMAIN GUSTY THROUGH THE REST OF THE FORECAST PERIOD.

BYRD

&&

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

$$

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