FXUS63 KLSX 282137
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
337 PM CST SAT NOV 28 2009

.DISCUSSION...
/337 PM CST SAT NOV 28 2009/

A WEAKENING SHORTWAVE WILL PASS THRU TONIGHT IMMEDIATELY FOLLOWED BY 
A PIECE OF ENERGY FROM THE FOUR CORNERS REGION SUNDAY AND A NRN 
STREAM TROF ON SUNDAY NIGHT. NWLY MID LEVEL FLOW WILL THEN PERSIST 
FOR MONDAY UNTIL FLOW BACKS AHEAD OF A PAIR OF STRONG SYSTEMS...ONE 
NRN STREAM AND THE OTHER SRN STREAM...APPROACH TO AFFECT US DURING 
THE FIRST PART OF THE EXTENDED PERIOD. AT THE SFC...A CDFNT WILL 
MOVE THRU LATE TONIGHT AND SUNDAY ENDING OUR BRIEF PERIOD OF WELL 
ABOVE NORMAL TEMPS. HI PRES WILL THEN DOMINATE THE AREA UNTIL 
TUESDAY NIGHT. 

MAIN FOCUS THRU TUESDAY WILL BE ON RAIN CHCS SUNDAY AND THEN TEMPS 
BEYOND THAT. 

MOISTURE RETURN ALOFT IS EXPECTED TO BE PRETTY ROBUST AHEAD OF THE 
CDFNT LATE TONIGHT AND INTO SUNDAY MORNING...AND WILL ALLOW PWATS TO 
RISE TO TWO STD DEVS ABOVE THE MEAN...OR TO NEAR AN INCH. WEAK H300 
JET COUPLING AND STRENGTHENING FRONTOGENESIS AT H850-700 SHOULD 
ALLOW CLOUDS TO RAPIDLY LOWER AND LIGHT RAIN TO DEVELOP PERHAPS 
TOWARDS DAYBREAK OVER CNTRL MO...OTHERWISE OVER MUCH OF THE AREA NW 
OF KSTL SUNDAY MORNING. THIS LIGHT RAIN WILL THEN INCREASE IN 
COVERAGE AS IT PUSHES SEWD WITH THE FRONT HEADING INTO THE AFTN AND 
EARLY EVENING HRS. TENDED TO FAVOR THE HIGHER MET MOS POPS AS WHILE 
EXPECTED QPF IS NOT HIGH...LIKELIHOOD OF PCPN WILL BE HIGH WITH MOST 
PLACES SE OF KSTL MEASURING...AND SOMEWHAT LESS TO THE NW. 

AFTER A FAIRLY RAPID TEMP FALL THIS EVENING...DECENT SUSTAINED SLY 
SFC WNDS AND INCRSG CLOUDS WILL FORCE TEMPS TO FLAT LINE THE REST OF 
THE NIGHT. STRONG LO LEVEL CAA BEHIND THE FRONT WILL RESULT IN 
FALLING TEMPS SUNDAY AFTN. HEADING INTO MONDAY AND TUESDAY... 
DECEPTIVELY DEEP MIXING ON MONDAY AND SLY FLOW ON TUESDAY SHOULD 
RESULT IN ABOVE NORMAL DAYTIME MAX TEMPS THRU MID WEEK. 

FOR THE EXTENDED PERIOD (TUESDAY NIGHT - SATURDAY)...MODELS IN 
AGREEMENT ON THE GENERAL SCENARIO THAT WILL UNFOLD THRU LATE IN THE 
WORKWEEK BUT DIFFER WIDELY ON NEXT WEEKEND. THE GENERAL SCENARIO 
WILL BE INITIALLY CUTOFF LO SYSTEM OVER NWRN OLD MEXICO LATE TUESDAY 
AFTERNOON WILL BE COAXED NEWD BY STRONG NRN STREAM KICKER SYSTEM... 
AFFECTING THE FA MAINLY ON WEDNESDAY...WITH BOTH SYSTEMS EVENTUALLY 
MERGING OVER THE OH VALLEY OR NERN CONUS ON THURSDAY. AN UPR TROF  
WILL THEN BE CARVED OUT ON THE BACKSIDE OF THIS SYSTEM THRU THE REST 
OF THE WORKWEEK...KEEPING THINGS COLD. MODELS...OF COURSE...DIFFER 
ON THE DETAILS BUT HAVE BEEN ADVERTISING SOMETHING ALONG THESE LINES 
FOR ABOUT 4 TO 5 DAYS NOW. THE TIMING HAS BEEN PUSHED BACK BY NEARLY 
48HRS DUE TO MODEL BIASES FROM CUTOFF LO SYSTEM IN THE SWRN CONUS 
WHICH IS NOT ENTIRELY UNEXPECTED. ONE OF THE TWO KEY ELEMENTS FOR 
THE WEDNESDAY SYSTEM IS NOW ONSHORE...WHERE IT CAN BE BETTER 
CAPTURED BY THE NOAM UA NETWORK...BUT THE NRN STREAM KICKER WILL NOT 
COME ONSHORE FROM THE NRN PAC UNTIL AT LEAST MONDAY...WHICH WILL 
ULTIMATELY DETERMINE HOW FAST THE SYSTEM MOVES OUT OF THE SWRN CONUS 
AND THE EXACT NERN BEND OF ITS TRACK AS IT DOES SO. THE GEM AND 
ECMWF HAVE DONE BETTER THAN THE GFS THIS AUTUMN ON STORM TRACKS/ 
TIMING IN THE MEDIUM RANGE...AND IF 12Z GFS IS ANY INDICATION...THIS 
SYSTEM WILL BE NO DIFFERENT...WITH THE GFS NOW TRENDING FURTHER NWD 
PER THE ECMWF/GEM. P-TYPES ARE A TOUGH CALL NOW...WITH TEMP FORECAST 
BEING TRENDED BELOW GUIDANCE...AND IN THE CASE OF WEDNESDAY...WELL 
BELOW. AS IT STANDS NOW...MUCH OF THE POTENTIAL PCPN FROM THIS 
SYSTEM WILL COME FROM THE DEFORMATION ZONE...AND WILL BE A RAIN VS. 
SNOW QUESTION. LACK OF COLD AIR BEFORE THE SYSTEM WILL HAVE ME 
LEANING MORE TOWARDS LIQUID PCPN FOR MOST OF THE EVENT WITH A 
CHANGEOVER TOWARDS THE END AND PERHAPS MINOR WET SNOW ACCUMS 
WEDNESDAY NIGHT...BUT THIS WILL BEAR WATCHING AS STRONG SYSTEMS CAN 
PULL IN COLD AIR QUICKLY. GIVEN CONSISTENCY ON GENERAL SCENARIO BUT 
DIFFS IN DETAILS...HAVE BUMPED POPS TO CHANCE CATEGORY FOR WED/WED 
NIGHT. FLURRIES/SPRINKLES POSSIBLE INTO THURSDAY ON BACKSIDE 
CYCLONIC FLOW. SATURDAY/S PCPN EVENT LOOKS QUESTIONABLE AT THIS 
TIME...AND HAVE GONE DRY FOR NOW. HOWEVER...AN ACTIVE PATTERN 
APPEARS IN THE OFFING INTO NEXT WEEKEND AND THE FOLLOWING WEEK.

TES

&&

.AVIATION...
/1118 AM CST SAT NOV 28 2009/

FOR THE 18Z TAFS...MAINLY A WIND FORECAST FOR MUCH OF THE TAF
PERIOD. SKIES WILL BE VFR WITH SWLY WINDS AROUND 10 TO 12 KTS WITH
A FEW GUSTS TO AROUND 18 KTS. FOR THE REMAINDER OF THE TAF...AN
APPROACHING CDFNT...CURRENTLY ACROSS THE PLAINS...WILL BRING A CHC
OF -RA TO STL/SUS. CAN NOT COMPLETELY RULE OUT PRECIP AT COU...BUT
ANY PRECIP THERE IS EXPECTED TO BE VERY LIGHT. EXPECT ANY PRECIP
TO BE ALONG AND JUST BEHIND THE CDFNT TO BE SPOTTY WITH CHANCES
BEING BETTER S OF STL/SUS. WILL THEREFORE KEEP THE PROB30 GROUP AT
STL AND HINT AT PRECIP IN THE SUS TAF. MODELS INDICATE IFR CIGS
WILL BE POSSIBLE BEHIND THE FRONT. AM NOT BUYING INTO THIS SOLUTION
YET...BUT HAVE TRENDED A LOWER CLOUD GROUP FOR STL. 

TILLY

&&

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

$$

WFO LSX