FXUS63 KLSX 241844
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1244 PM CST THU DEC 24 2009

.DISCUSSION...
/405 AM CST THU DEC 24 2009/

TODAY THROUGH FRIDAY...PRIMARY CONCERNS ARE HEAVY RAIN 
TODAY...COMPLEX STORM SYSTEM TONIGHT AND FRIDAY...AND LINGERING SNOW 
SHOWERS FRI NIGHT THROUGH SUN.

TODAY...REGIONAL RADAR MOSAIC DEPICTED A CONTINUOUS RAIN SHIELD FM 
MO/AR BORDER THROUGH AR INTO LA. PW VALUES ARE FCST TO CONTINUE 
INCRSG THROUGH TONIGHT...REACHING 0.9 TO 1 INCHES OVER MOST OF THE 
CWA AND EVEN HIGHER OVER SERN COUNTIES. THESE VALUES ARE AT LEAST 2 
STANDARD DEVIATIONS ABOVE DECEMBER CLIMATOLOGY...THUS STILL EXPECT 
MODERATE TO HEAVY RAINFALL TODAY GIVEN AMPLE MOISTURE AND INCREASING 
SYNOPTIC LIFT FM APCHG STORM SYSTEM. WILL CONTINUE WITH GOING FLOOD 
WATCH.

TONIGHT...PRIMARY FCST PROBLEM IS EVOLUTION OF SRN PLAINS STORM 
SYSTEM. WATER VAPOR IMAGERY SHOWED FOUR DISTINCT PV ANOMALIES OF 
INTEREST. THE TWO STRONGEST FEATURES WERE THE DIGGING SHORTWAVE
OVER WRN TX AND THE NRN SHORTWAVE DROPPING FM SASKATCHEWAN INTO
MT/WY. THE OTHER FEATURES WERE LOCATED OVER IA/NE/SD AND ERN TX.
TWO STRONGEST FEATURES ARE EXPECTED TO INTERACT /FUJIWHARA EFFECT/
AND MERGE WHILE LIFTING NWD INTO THE LOWER MSVLY. MODELS CONTINUE
TO TREND EWD WITH TRACK OF SFC LOW...WHICH HAS SIGNIFICANT IMPACTS
ON LOCATION OF THE HEAVY SNOW BAND. GIVEN MODEL DIFFICULTY IN
CAPTURING SWD EXTENT OF DIGGING OVER THE LAST FEW DAYS...CONCERNED
THAT MODELS HAVE BEEN SLOW TO CATCH ON TO INTENSITY OF SRN
SHORTWAVE AND COULD STILL BE TOO FAR W WITH SFC LOW TRACK.
GENERALLY FOLLOWED A GEM/NAM BLEND SINCE THE NAM BEST CAPTURED THE
INFLUENCE OF THE WEAKER SHORTWAVES AND THE GEM HAS BEEN
CONSISTENTLY CATCHING ON TO THE FARTHER EWD TRACK. WITH THAT IN
MIND...HAVE STARTED TRENDING THE FCST TOWARDS A MORE ERN SOLUTION
THAT BRINGS 2-4 INCHES OF ACCUMULATING SNOW TO FAR WRN COUNTIES.
RAIN WILL CHANGE TO SNOW BEHIND THE COLD FRONT AFTER MIDNIGHT BUT
A PERIOD OF SLEET IS POSSIBLE AS THE COLD AIR QUICKLY UNDERCUTS
WARMER LAYERS ALOFT. TIGHT PRESSURE GRADIENT WILL CREATE STRONG
GUSTY WINDS TONIGHT THROUGH FRI NIGHT. DUE TO THE COMBINATION OF
SLEET...WIND...AND SNOW...HAVE ISSUED A WINTER STORM WATCH FOR
CENTRAL AND NORTHEAST MISSOURI COUNTIES.

KANOFSKY

FRIDAY NIGHT THROUGH SUNDAY...
SPOKES OF VORTICITY COUPLED WITH STEEP LAPSE RATES WILL BRING 
SCATTERED SNOW SHOWERS/SQUALLS TO THE AREA AS THE NEARLY STACKED LOW 
PRESSURE SYSTEM PINWHEELS ACROSS IOWA. HAVE INCREASED POPS AND QPF 
AS MODEL CONSENSUS AND PAST EXPERIENCE TELLS ME THAT ALTHOUGH NOT 
EVERYONE WILL SEE ACCUMULATING SNOW FROM THESE SNOWBANDS...THOSE 
THAT DO WILL LIKELY HAVE A FEW INCHES TO CONTEND WITH. COUPLE THE 
LIGHT SNOW ACCUMULATION WITH THE BRISK WIND AND WINTER ADVISORY TYPE 
CONDITIONS MAY BE REALIZED AT TIMES THIS HOLIDAY WEEKEND.

CVKING

&&

.AVIATION...
/1219 PM CST THU DEC 24 2009/

FOR THE 18Z TAFS...LATEST SURFACE ANALYSIS SHOWS DEEPENING LOW
OVER SOUTHWEST ARKANSAS...FAR NORTHEAST TEXAS. INVERTED SURFACE
TROUGH EXTENDED NORTHWARD FROM SURFACE LOW THROUGH WEST CENTRAL
MISSOURI AND INTO CENTRAL IOWA. EAST TO SOUTHEAST FLOW CONTINUES
TO MILD TEMPERATURES OVER AREA. LATEST MODEL DIAGONSIS SHOWS THAT
SURFACE LOW IS EXPECTED TO TRAVEL NEARLY NORTH AND MOVE JUST WEST
OF COLUMBIA MO LATE TONIGHT AND INTO PARTS OF EAST CENTRAL IOWA BY
CHRISTMAS MORNING. THE GEM HAD SOME PROBLEMS THIS TIME IN TRACKING
THE POSITION OF THE SURFACE LOW. YESTERYDAY'S SOLUTION SHOWED THAT
THE TRACK WAS TO BE OVER STL AREA AND THIS MORNING RUNS PLACE IT
WEST OF THE OTHER MODEL SOLUTIONS. LOCAL WRF..NAM..EUROPEAN LOOKS
VERY GOOD FOR THE LATEST SURFACE LOW TRACK. 8H LOW LEVEL JET FROM
THE SOUTH CONTINUES TO SUPPLY PLENTLY OF MOISTURE INTO LOWER AND
MIDDLE MISSISSIPPI VALLEY REGION. WIDESPREAD RAINFALL EXTENDS FROM
PARTS WEST CENTRAL ILLINOIS THROUGH ST. LOUIS AREA AND INTO
CENTRAL AND EASTERN ARKANSAS. MUCH OF EASTERN MISSOURI WILL BE IN
RAINFALL THROUGH THE EVENING HOURS. SOME HEAVIER RAIN IS EXPECTED
LATE THIS AFTERNOON AND THIS EVENING OCCASIONALLY REDUCING
VISIBILITIES. WILL CONTINUE TO GO WITH LOW CEILING AND LOW
VISIBILITIES OVER THE AREA. BELIEVE THAT GUIDANCE MIGHT BE A
LITTLE TOO HIGH CONCERNING SURFACE WIND FORECAST FOR THIS
AFTERNOON AND THIS EVENING. AS SURFACE LOW MOVES NORTHWARD COLD
FRONT WILL MOVE THROUGH THE COU AREA AROUND 0900 UTC AND OVER STL
AROUND 1400 UTC. JUST MOVED IT BACK BY A FEW HOURS FOR STL AREA.
ALSO VERY GUSTY WINDS ARE EXPECTED ON THE BACK SIDE OF THE SURFACE
LOW AND SURFACE PRESSURE GRADIENT REMAINS VERY TIGHT. EXPECT
SURFACE GUSTS TO 25 TO 30 KTS FROM THE WEST LATER TOMORROW MORNING
AND INTO THE AFTERNOON HOURS. SOME SCATTERED SHOW SHOWERS ARE
LIKELY FOR MUCH OF MISSOURI MAINLY AFTER 1200-1500 UTC TIME FRAME.

PRZYBYLINSKI

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...FLOOD WATCH UNTIL MIDNIGHT CST TONIGHT FOR AUDRAIN-BOONE-
     CALLAWAY-COLE-CRAWFORD-FRANKLIN-GASCONADE-IRON-JEFFERSON-
     KNOX-LEWIS-LINCOLN-MADISON-MARION-MONITEAU-MONROE-
     MONTGOMERY-OSAGE-PIKE-RALLS-REYNOLDS-SHELBY-ST. CHARLES-ST. 
     FRANCOIS-ST. LOUIS-ST. LOUIS CITY-STE. GENEVIEVE-WARREN-
     WASHINGTON.

     WINTER STORM WATCH FROM MIDNIGHT CST TONIGHT THROUGH FRIDAY 
     AFTERNOON FOR AUDRAIN-BOONE-CALLAWAY-COLE-KNOX-LEWIS-MARION-
     MONITEAU-MONROE-OSAGE-RALLS-SHELBY.

IL...FLOOD WATCH UNTIL MIDNIGHT CST TONIGHT FOR ADAMS IL-BOND IL-
     BROWN IL-CALHOUN IL-CLINTON IL-FAYETTE IL-GREENE IL-JERSEY 
     IL-MACOUPIN IL-MADISON IL-MARION IL-MONROE IL-MONTGOMERY IL-
     PIKE IL-RANDOLPH IL-ST. CLAIR IL-WASHINGTON IL.

&&

$$

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