FXUS63 KLSX 240539
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1140 PM CST WED DEC 23 2009

.UPDATE...
/850 PM CST WED DEC 23 2009/

EDGED MIN TEMPS OVERNIGHT UP A LITTLE BIT...OTHERWISE FORECAST
LOOKS TO BE RIGHT ON THE MONEY. MOST AREAS EXPERIENCING A BREAK IN
THE ACTION NOW BUT SMALL CLUSTER OF TSRA MOVING INTO CNTRL MO ATTM
AND HAS RESULTED IN SMALL HAIL REPORTS BEING RECEIVED. THE NEXT
MAJOR SLUG OF RAINFALL AND EMBEDDED TSRA IS DEVELOPING NOW IN AR
AND WILL PUSH NWD INTO THE FA AFTER MIDNIGHT AND IS EXPECTED TO
PERSIST THRU THURS MORNING AT LEAST. THIS WILL RESULT IN
WIDESPREAD ONE TO TWO INCH RAINFALL AMOUNTS WITH LOCALLY HIGHER
VALUES...AND COMBINED WITH ANTECEDENT CONDS...COULD VERY WELL LEAD
TO SOME FFW ISSUANCES.

NEW 00Z NAM IS INTRIGUING AT BEST...AND DISTURBING AT LEAST...
WITH DEF ZONE QUITE A BIT FARTHER E INTO ERN MO THAN PREVIOUS
RUNS. WILL NEED TO WAIT AND SEE IF THIS IS AN OUTLIER OR A TREND
OVERNIGHT AND ACT ACCORDINGLY. IF TRUE...COULD SEE SEVERAL INCHES
OF SNOW EARLY CHRISTMAS MORNING.

TES
&&

.DISCUSSION...
/318 PM CST WED DEC 23 2009/

LOTS OF QUESTIONS WITH THIS FORECAST INCLUDES THE THREAT OF
FLOODING...ACCUMULATING SNOWFALL AND GUSTY WINDS. HAVE FOLLOWED
ALONG WITH A BLEND OF THE LATEST ECMWF/NAM GUIDANCE WHICH FALL IN
THE MIDDLE OF THE OTHER GUIDANCE. GFS SUFFERS FROM CONVECTIVE
FEEDBACK THE NEXT FEW DAYS WHICH IS REFLECTED IN IT'S QPF FIELDS.
IT ALSO HAS TROUBLE PHASING THE TWO UPPER LOWS BY FRIDAY NIGHT.
THE CANADIAN GEM IS ON THE EASTERN SIDE OF THE MODEL SUITE WITH THE
TRACK OF THE UPPER LOW...THOUGH NOT AS FAR EAST AS IT DID ON THE
00Z RUN.

REGARDING THE FLOODING POTENTIAL...SEVERAL LOCATIONS IN CENTRAL 
MISSOURI AND SOUTH CENTRAL ILLINOIS HAVE ALREADY SEEN 1 TO 2 INCHES 
OF RAINFALL.  FLOOD WATCH HAS ALREADY BEEN EXPANDED TO INCLUDE THE 
REMAINING CENTRAL MO COUNTIES AND WILL BE EXTENDED THROUGH TOMORROW 
EVENING. ADDITIONAL SHRA/TSRA HAVE DEVELOPED TO THE SOUTHWEST AND
WILL BE MOVING INTO THE REGION THIS EVENING.  MODELS STILL SHOW
IMPRESSIVE FORCING AND UNSEASONABLY HIGH PWATS ADVECTING INTO THE
AREA THROUGH TOMORROW EVENING. ADDITIONAL RAINFALL IS EXPECTED TO
RANGE FROM 1.5-2" OVER CNTRL/NERN MO TO OVER 2.5" IN SERN MO/S CNTRL
ILLINOIS WHERE THE LOW LEVEL FORCING WILL BE MORE FOCUSED.

WINDS WILL CERTAINLY PICK UP IN THE WARM SECTOR TOMORROW...WITH 
SUSTAINED WINDS IN THE 15 TO 30 MPH RANGE3 WITH SOME HIGHER
GUSTS. NOT QUITE ENOUGH TO REQUIRE AN ADVISORY SO WILL HIT THE
WORDING HARD IN THE HWO. COLD FRONT WILL MOVE ACROSS THE CWA FROM
WEST TO EAST ON THURSDAY EVENING AND PRESSURE GRADIENT BEHIND
FROPA WILL REMAIN TIGHT THROUGH FRIDAY NIGHT IN THE COLD AIR
ADVECTION.

WINTER WISE...RAIN WILL CHANGE TO SNOW FROM WEST TO EAST AS THE 
FRONT PASSES THROUGH TOMORROW NIGHT.  THE BEST MID LEVEL FORCING AND 
850 MB LOW TRACK CONTINUE TO SUGGEST THAT THERE WILL BE A TIGHT 
GRADIENT OF SNOWFALL OVER CENTRAL MO.  LOOKS LIKE ADVISORY CRITERIA 
SNOW WILL STAY JUST WEST OF THE CWA DURING THIS PERIOD. MAY STILL
SEE 1-2 INCHES TOMORROW NIGHT INTO FRIDAY ON THE EASTERN EDGE OF
THE DEFORMATION ZONE. STILL LOOKS LIKE A DECENT SET UP FOR SNOW
SHOWERS FRIDAY INTO SATURDAY TO THE NORTH OF I-70 CONSIDERING THE
STEEP LAPSE RATES IN THE LOW LEVELS IN ADDITION TO THE ABUNDANT
MOISTURE AND CYCLONIC CURVATURE.

HAVEN'T CHANGED THE FORECAST MUCH EARLY NEXT WEEK AS I EXPECT THERE 
STILL WILL BE LINGERING SNOW SHOWERS OR FLURRIES AS UPPER LOW
REMAINS IN RELATIVELY CLOSE PROXIMITY TO US THROUGH SUNDAY NIGHT
BEFORE IT LIFTS NEWD. RIDGING THEN BUILDS IN PROVIDING DRY WEATHER
FOR AT LEAST MONDAY AND TUESDAY. BOTH THE ECMWF/GEFS MEAN ARE
SHOWING ANOTHER TROUGH REACHING THE MIDWEST BY WEDNESDAY...BUT
LACK OF DECENT MODEL CONTINUITY AND BLOCKINESS OF THE UPPER
PATTERN OVER THE WEEKEND TELLS ME TO KEEP FORECAST DRY FOR NOW.

BRITT
&&

.AVIATION...
/1140 PM CST WED DEC 23 2009/

FOR THE 06Z TAFS...CIGS HAVE TEMPORARILY LIFTED TO MVFR/VFR AT 
MOST TAF SITES...BUT SHOULD GO BACK DOWN TO IFR/LIFR BY 08Z AT 
KCOU...09Z AT KUIN AND BY 11Z AT KSTL/KSUS FOR THE REMAINDER OF THE  
TAF FORECAST PERIOD. MAIN ISSUE IS VSBYS WITH THE HEAVIER RAIN FROM 
TIME TO TIME...EXPECT ANOTHER ROUND OF HEAVY RAIN BY 12Z/13Z AT 
KCOU...KSTL AND KSUS AND AROUND 19Z AT KUIN. THIS BATCH OF HEAVY RAIN
COULD PERSIST THROUGH THE REMAINDER OF THE TAF FORECAST PERIOD AS 
SYSTEM LIFTS SLOWLY NORTHWARD THROUGH THE REGION. AS FOR WINDS... 
GUSTY EAST TO SOUTHEAST WINDS WILL BEGIN TO CHANGE DIRECTION AS THE
SURFACE LOW TRACKS FROM NORTHERN AR INTO EAST CENTRAL MO THIS 
EVENING (CHRISTMAS EVE).

BYRD
&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...FLOOD WATCH THROUGH THURSDAY EVENING 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.

IL...FLOOD WATCH THROUGH THURSDAY EVENING 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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