FXUS63 KLSX 260537
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1137 PM CST WED NOV 25 2009

.DISCUSSION...
/353 PM CST WED NOV 25 2009/

...SYNOPSIS...
TEMPS REACHED THE UPPER 40S TO LOWER 50S IN ADVANCE OF A COLD FRONT 
ATTACHED TO A UPPER LOW/VORT MAX EVIDENT IN WATER VAPOR IMAGERY 
OVER IA. COLD FRONT IS CURRENTLY LOCATED ROUGHLY ALONG THE MS 
RIVER.  BAND OF CLOUDS AND RADAR ECHO ACCOMPANY THE FRONT...THOUGH 
NOT MUCH OF THE PRECIP HAS BEEN REACHING THE SURFACE. THERE IS A 
BREAK IN THE CLOUDS BEHIND THE FRONT...BUT THIS SHOULD BE REPLACED 
BY A STATUS DECK OVERNIGHT AS WRAP-AROUND MOISTURE CONTINUES TO 
PUSH SE.

...SHORT TERM (TONIGHT THRU SATURDAY)...
CLOSED LOW OVER IA THIS AFTERNOON WILL CONTINUE TO DROP SE 
OVERNIGHT..THEN EXIT EAST TOMORROW.  THERE/S A DECENT SHOT OF COLD 
AIR FOLLOWING THE SYSTEM WITH 850 TEMPS -4 TO -6 OVER THE CWA BY 12Z 
THURSDAY.  TEMPS DON/T BOTTOM OUT TONIGHT DUE TO CLOUD COVER AND 
GUSTY WINDS. TEMPS WILL STRUGGLE TO RISE THANKSGIVING GIVEN 
CONTINUED CLOUD COVER AND CAA. THERE MAY BE SOME LIGHT QPF IN THE 
FORM OF RAIN/SNOW OVER THE NORTHERN AND EASTERN CWA TONIGHT AND 
TOMORROW.  THIS SHOULD NOT BE A BIG DEAL AND MAY ONLY BE SPRINKLES 
OR FLURRIES.  NO ACCUM IS EXPECTED. OVERALL...THE HOLIDAY LOOKS TO 
BE A PRETTY RAW DAY.

THURSDAY NIGHT/FRIDAY MORNING WILL BE THE COLDEST OF THE SEASON WITH 
CLEAR SKIES AND LIGHT WINDS.  MOST LOCATIONS WILL DROP INTO THE 20S 
WITH THE EXCEPTION BEING THE STL METRO WHERE AT LEAST LOW 30S LOOK 
LIKELY.  

THE COLD AIR INTRUSION IS BRIEF WITH RETURN FLOW BEGINNING AS EARLY 
AS LATE THURSDAY NIGHT ACROSS CENTRAL MO.  IF THIS OCCURS...THEN 
LOWS IN THE COU/JEF AREA MAY NOT BOTTOM OUT AS CURRENTLY INDICATED.  
WARMING IS IN RESPONSE TO A H500 RIDGE THAT BUILDS INTO THE CENTRAL 
CONUS. THE WARMING CONTINUES FRIDAY AND PEAKS SATURDAY WITH 850 
TEMPS NEAR +12.  THERE SHOULD BE A RATHER STEEP TEMP GRADIENT FROM 
E-W ON FRIDAY WITH SOUTHERN ILLINOIS REMAINING NEAR 50 AND CENTRAL 
MO NEAR 60.  HIGHS ON SATURDAY SHOULD BE AT LEAST IN THE MID TO 
UPPER 50S WITH LOW 60S POSSIBLE ALONG THE MO RIVER FROM CENTRAL MO 
INTO THE STL METRO. 

WENT A LITTLE ABOVE GUIDANCE TONIGHT WITH CLOUDS AND WIND...EXCEPT 
FOR CENTRAL MO...WENT CLOSER TO GUIDANCE AS THEY HAVE THE BEST 
CHANCE OF PARTIAL CLEARING TOWARDS DAYBREAK. THURSDAY/NIGHT WENT 
BELOW GUIDANCE. CLOUDS TOMORROW SHOULD HELP KEEPS TEMPS DOWN AND 
OPTIMAL RADIATIONAL COOLING CONDITIONS BY FRIDAY MORNING SHOULD 
ALLOW TEMPS TO PLUNGE.  WENT BACK ABOVE GUIDANCE FOR FRIDAY AND 
SATURDAY WITH MOSTLY CLEAR SKIES AND SWLY FLOW AT THE SURFACE AND 
ALOFT.

...EXTENDED (SATURDAY NIGHT THRU WEDNESDAY)...
MODELS IN DECENT AGREEMENT THRU MONDAY MORNING.  LONG WAVE TROUGH 
CONTINUES TO DIG IN THE DESERT SW. THE UPPER PATTERN TRANSITIONS TO SW 
FLOW AS UPPER RIDGE AXIS TRANSLATES EAST.  FLOW BECOMES SPLIT EARLY 
NEXT WEEK WITH NORTHERN STREAM SW DRAGGING A COLD FRONT THRU THE 
AREA SUNDAY.  PRECIP DEVELOPS LATE SUNDAY AND CONTINUES INTO 
MONDAY NIGHT.  BULK OF THE PRECIP LOOKS TO STAY SOUTH AND EAST OF 
THE STL METRO. THERE MAY BE ENOUGH COLD AIR ON THE BACK SIDE OF THIS 
SYSTEM TO MIX WITH OR CHANGE TO SNOW AS THE SYSTEM DEPARTS.  WAY TOO 
EARLY TO TALK ACCUMS.  ECMWF IS FURTHEST NORTH WITH QPF PLACEMENT.  
NEW 12Z GFS KEEPS BULK OF MEASURABLE PRECIP JUST SOUTH OF THE 
CWA...WHICH IS SIMILAR TO THE CMC.  SO...MAY HAVE TOO HIGH OF POPS 
TOO FAR NORTH DURING THE PERIOD.  HAVE TIME TO REFINE THOUGH.  BASE 
OF THE TROUGH CLEARS THE AREA TUESDAY...THEN ATTENTION TURNS TO 
SOUTHERN STREAM SW.  

THE SOUTHERN STREAM ENERGY IS MORE PROBLEMATIC. THE ECMWF PASSES THE 
UPPER LOW FROM TX THROUGH THE OHIO VALLEY AND KEEPS THE PRECIP WELL 
EAST THE AREA.  THE GFS HOWEVER...TRACKS THE UPPER LOW THROUGH THE 
MID-MIS VLY AND INTO THE CENTRAL GREAT LAKES.  IT SIGNIFICANTLY 
DEEPENS THE ASSOC SFC LOW IN THE PROCESS.  THIS WOULD PUT MORE 
PRECIP IN THE AREA WEDNESDAY AND THURSDAY.  THIS IS A SIMILAR BUT 
SLOWER SOLUTION TO THE 00Z RUN.  OVERNIGHT TEMPS COULD MAKE THINGS 
INTERESTING FOR P-TYPE...BUT LEFT THE FCST DRY UNTIL THERE IS MORE 
RUN-TO-RUN CONTINUITY.

TEMPS THRU THE PERIOD SHOULD REMAIN NEAR SEASONABLE LEVELS AS AIR 
MASS SOURCE REGION IS OFF THE PACIFIC.  THIS MEANS HIGHS IN THE 40S 
TO LOW 50S AND LOWS IN THE UPPER 20S TO MID 30S.

MILLER

&&

.AVIATION...
/1132 PM CST WED NOV 25 2009/

FOR THE 06Z TAFS...ONLY MINOR TWEAKS TO PREV TAFS FOR THIS
FORECAST. PRECIP STARTED OUT AS SN AT UIN...AND HAVE LEFT IT AS SN
OVERNIGHT. OTHERWISE...CIGS GRADUALLY LOWERING AT SITES OVERNIGHT
THEN LIFTING MID TO LATE MORNING. ALL SITES SHUD BE VFR BY AROUND
NOON THURS THEN CLEAR...OR AT MOST SOME CI...BY AFTERNOON HOURS.
GUSTY WINDS SHUD DIMINISH AROUND SUNSET THURS AS THE PRESSURE GRAD
RELAXES. 

TILLY

&&

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

$$

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