FXUS63 KLSX 270521
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1121 PM CST THU NOV 26 2009

.UPDATE...
/822 PM CST THU NOV 26 2009/

HAVE ISSUED AN UPDATED FORECAST BASED ON LATEST SATELLITE TRENDS
WHEREBY MUCH OF THE FA HAS ALREADY CLEARED AND THE REST OF IT
STILL UNDER THE LOW SC CLOUD DECK WILL DO SO BY MIDNIGHT. A FEW
HIGH THIN CI CLOUDS WILL DRIFT OVERHEAD THE REMAINDER OF THE NIGHT
BUT WILL HAVE LITTLE IMPACT ON OPACITY. TEMPS ARE ALSO FALLING AT
A FASTER RATE THAN EVEN THE COLDEST MOS IN THE AREAS THAT HAVE
ALREADY CLEARED...AND SO HAVE EDGED TEMPS DOWN ANOTHER DEG OR TWO.

IF THIS FORECAST HOLDS...THIS WILL BE THE FIRST FREEZE FOR SAINT
LOUIS THIS AUTUMN...EITHER TYING THE ALL TIME RECORD FOR THE
LATEST OCCURRENCE OF THE FIRST AUTUMNAL FREEZE SHOULD KSTL DROP TO
32F BY MIDNIGHT OR BREAK THE ALL TIME RECORD IF THAT OCCURS AFTER
MIDNIGHT. ALL OTHER SITES WITHIN THE FA HAVE ALREADY HAD THEIR
FIRST FREEZE OF THE SEASON.

TES

&&

.DISCUSSION...
/219 PM CST THU NOV 26 2009/

SYNOPSIS...

PER 19Z WATER VAPOR IMAGERY MAIN H5 LOW AND ASSOC CYCLONIC ENERGY 
CONTINUED TO PROGRESS EWD INTO THE SRN GRT LKS RGN AND OH-TN VLY.  
AMPLIFIED H5 RIDGE OF HI PRES...ASSOC WITH SUBSTANTIALLY WARM H85 
TEMPS AS ANALYZED AT 12Z...WAS CENTERED ACRS THE ERN INTR-MTN WEST.  
SATELLITE TRENDS EXHIBITED CLOUDS SLOWLY ERODING EWD ALONG AND WEST 
OF THE MS RVR IN CONCERT WITH THE EWD PROGRESSION OF THE 
AFOREMENTIONED H5 RIDGE.  TEMPS WERE OBSERVED IN THE LOW 40S FOR 
THOSE LOCALES UNIMPEDED BY CLOUDS...WITH ALL OTHER LOCATIONS INTO 
THE UPR 30S UNDER NWLY WINDS GUSTING ESPECIALLY AT 20-25 MPH EAST
OF THE MS RVR.

SHORT TERM (TONIGHT - SAT)...

UPR LVL DISTURBANCE AND ASSOC CYCLONIC FLOW WILL CONTINUE EWD INTO 
NEW ENGLAND.  FOR THE FA LLVL CLOUDS SHUD ERODE THRU THE EVNG HRS 
UNDER WEAKENING NWLY FLOW AS DRIER AIR ADVECTS INTO THE REGION 
ASSOCIATED WITH AN AMPLIFIED H5 RIDGE OF HI PRES.  ANTICIPATE WITH 
CLEARING SKIES AND WEAKENING WINDS OVERNIGHT TEMPS TO FALL TO THEIR 
LOWEST VALUES THUSFAR THIS SEASON.

THRU FRI WINDS WILL BEGIN TO TURN W-SWLY RESULTING IN STRONG WAA 
FROM THE SRN-CNTRL PLAINS.  HAVE INCREASED HIGH TEMPS FOR FRI A FEW 
DEGREES WITH ANTICIPATED LLVL DRY ADIABATIC MIXING TO H925 WITH
ASSOC TEMPS AT +8-10C. FOLLOWING CLIMATOLOGY AND EXPECTED CLEAR
CONDITIONS FOR FRI NIGHT ANTICIPATE TEMPS TO FALL ROUGHLY 15-20
DEGREES FOR OVERNIGHT LOWS. SWLY FLOW AND WAA WILL CONTINUE INTO SAT
WITH CONTINUED MIXING TO H925 AND TEMPS +10-14C ACRS THE FA. HAVE
BROUGHT TEMPS UP CONSIDERABLY INTO THE UPR 60S REGION-WIDE AND
WOULD NOT BE SURPRISED TO SEE SOME LOCATIONS ON SAT AROUND 70F.

SFC HI PRES WILL RETREAT ACRS THE SERN CONUS AS SFC LOW PRES AND 
ASSOC CDFRNT WILL DVLP THRU THE CNTRL PLAINS AHEAD OF A H5 TROF
DIGGING INTO THE WRN CONUS. AFOREMENTIONED SWLY FLOW ON SAT WILL
ALLOW FOR THE BEGINNING OF SUFFICIENT MOIST ADVECTION NWD ALONG
AND AHEAD OF THE DVLPG CDFRNT. EXPECT CLOUDS TO INCREASE TOWARDS
THE LATE AFTN HRS INTO THE EVNG ON SAT AS MOISTURE WILL
ISENTROPICALLY LIFT ACRS THE FA. DO NOT EXPECT ANY POP CHCS AS
ATMOSPHERE ACRS THE REGION WILL STILL BE SUBSTANTIALLY DRY.
 

EXTENDED (SAT NGT - FRI)...

HAVE FOLLOWED CLOSELY WITH A BLEND OF ECMWF/CANADIAN/GFSENS THRU 
MID-WEEK FOR EXTENDED WITH ECMWF THEREAFTER INTO THE FOLLOWING WEEKEND.

H5 RIDGE SHUD DEAMPLIFY THRU ERN CONUS WITH RESULTANT ZONAL FLOW 
SETUP THRU MID-MS VLY.  SLOW MOVING SFC CDFRNT SHUD PROGRESS SEWD 
THRU THE FA SUN AND EJECT QUICKLY EWD AS FIRST LOBE OF UPR LVL 
ENERGY DIGS SWD OUT OF THE NRN CONUS. NOT SO CONFIDENT ON POP CHCS
SAT NGT INTO EARLY SUN WITH LACK OF MID-UPR LVL FORCING...BUT AS
H5 TROF DIGS SWD SHUD EXPECT BETTER MID-LVL FRONTOGENESIS AND
STEEPENING LAPSE RATES AHEAD OF SFC COLD AIR. IN ADDITION MID-LLVL
MOISTURE WILL SURGE NWD ALONG AND AHEAD OF SFC CDFRNT. THUS HAVE
INCREASED POPS FOR SUN INTO MON MORNING TIMEFRAME. HAVE LOWERED
TEMPS A FEW DEGREES WITH SUN HIGHS AND BOTH MON LOWS AND HIGHS IN
ANTICIPATION OF A FASTER MOVING SYSTEM AND BOTH GUSTY NWLY WINDS
AND CAA IN WAKE OF SFC CDFRNT. ABUNDANCE OF LLVL MOISTURE AND
STEEP LAPSE RATES SHUD ALLOW CLOUDS TO HANG AROUND INTO LATE MON
INTO EARLY TUE. WILL NEED TO MONITOR CLOSELY AS TO IMPACTS TO TUE
LOWS IF CLEARING SHUD OCCUR FASTER...MDL MEMBERS SUGGESTIVE OF
SUFFICIENT ISENTROPIC DOWNGLIDE IN WAKE OF DEPARTING SYSTEM...BUT
WOULD NOT BE SURPRISED WITH LINGERING STRATUS-STRATOCU THRU FA.

SFC HI SHUD SLINK SOUTH OF THE FA FOR TUE WITH RETURN SLY FLOW 
ANTICIPATED.  HAVE WARMED TUE HIGH A FEW DEGREES IN ANTICIPATION OF 
CLEAR SKIES AND SELY FLOW.  INTO WED SFC HI SHUD PROGRESS EWD AS THE 
SECOND LOBE OF UPR LVL ENERGY BEGINS TO LIFT INTO THE MAIN LONGWAVE 
PATTERN.  FOLLOWED CLOSELY WITH ECMWF IN DEVELOPING A SFC LOW OFF 
THE TX SHORELINE LIFTING NWD THRU THE MID-MS VLY THURS.  THIS WOULD 
LEAVE MUCH OF THE FA ON THE BACKSIDE OF THE SFC LOW.  HAVE INCREASED 
POPS FOR THE WED INTO THURS TIMEFRAME AND KEPT TEMPS ABOVE FREEZING 
UNTIL THE SYSTEM EXITS THURS NIGHT WHEN THEREAFTER TEMPS ARE 
EXPECTED TO FALL FOR FRI.  NEVERTHELESS CONFIDENCE IS LOW AS MDL 
MEMBERS POORLY HANDLE THE OUTCOMES FOR THE END OF THE WEEK AND THERE 
IS A FAIR AMNT OF SPREAD.

SIPPRELL

&&

.AVIATION...
/1047 PM CST THU NOV 26 2009/

FOR THE 06Z TAFS...MINOR IF ANY CHANGES TO PREV FORECAST. ONLY
CLOUDS EXPECTED WILL BE CI. WINDS WILL GRADUALLY BACK TO
EVENTUALLY BECOME SLY BY FRI AFTERNOON. WINDS WILL BE VEER
SLIGHTLY FRI EVE INTO THE OVERNIGHT HOURS. BASED ON LATEST MODEL
GUIDE...LLWS MAY BE POSS OVERNIGHT FRI INTO SAT MORNING. 

TILLY

&&

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

$$

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