FXUS63 KLSX 251151
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
551 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...
/540 AM CST FRI DEC 25 2009/

FOR THE 12Z TAFS...
A COUPLE OF THINGS TO WATCH OUT FOR THIS MORNING...FIRST WILL BE
RAPIDLY FALLING TEMPERATURES AND STRONG WEST-SOUTHWEST WINDS
BEHIND THE COLD FRONT WHICH IS MOVING THROUGH THE REGION.
TEMPERATURES WILL QUICKLY FALL BELOW FREEZING AFTER FROPA WHICH
WILL CAUSE ANY WATER REMAINING ON RUNWAYS/TAXIWAYS/RAMPS TO FREEZE
RAPIDLY. ADDITIONALLY...THE STRONG WEST-SOUTHWEST WINDS WILL CAUSE
CROSSWIND ISSUES ON ANY NORTHWEST/SOUTHEAST RUNWAYS.

SECOND...SCATTERED SNOW SHOWERS WILL BE ONGOING BEHIND THE FRONT
TODAY AND AT LEAST PART OF TONIGHT. PREVAILING CIGS WILL LIKELY BE LOW
MVFR...AND VSBYS SHOULD BE 6SM OR ABOVE. HOWEVER...HEAVIER SNOW
SHOWERS COULD BRING CIGS AND VSBYS DOWN TO IFR RANGE FOR BRIEF
PERIODS.

CARNEY

&&

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

$$

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