257
FXUS63 KLSX 210207
AFDLSX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
807 PM CST FRI NOV 20 2009
UPDATE
/807 PM CST FRI NOV 20 2009/
OVERNIGHT ADJUSTMENTS HAVE BEEN MADE TO THE FORECAST IN LIGHT OF
THE RAPID DEVELOPMENT OF HIGH SC/LOW AC CLOUDS THAT HAVE DEVELOPED
PRIMARILY OVER THE I-70 CORRIDOR IN THE PAST FEW HOURS. THIS IS A
RESPONSE TO NARROW BUT INTENSE ISENTROPIC UPGLIDE MOST NOTICEABLE
AT THE 290K LEVEL. MODELS TAKE THIS LIFT AND MAINTAIN IT THRU THE
NIGHT AROUND THE I-70 CORRIDOR AND EVENTUALLY EXPAND IT INTO NERN
MO/WCNTRL IL. THESE CLOUDS SHOULD EFFECTIVELY KILL WIDESPREAD FOG
FORMATION FOR THE I-70 CORRIDOR...BUT FOR AREAS THAT CAN COOL
RAPIDLY ENOUGH IN THE FAR NRN FA AROUND QUINCY BEFORE THE CLOUDS
ROLL IN...AREAS OF FOG STILL EXPECTED TO FORM ALTHOUGH VSBYS WILL
LIKELY IMPROVE NEAR SUNRISE WHEN VSBYS ARE NORMALLY AT THEIR
WORST. SERN MO WILL BE JUST S OF THE BETTER ISENTROPIC UPGLIDE AND
SO WILL HAVE ENOUGH HOLES IN THE CLOUDS TO ALSO COOL OFF AND SO
HAVE ADDED AREAS OF FOG GIVEN THEIR RELATIVELY HIGH CROSSOVER
TEMPS IN THE MID 40S. MIN TEMP ADJUSTMENTS HAVE BEEN MADE TO
INCREASE BY SEVERAL DEGS FOR THE I-70 CORRIDOR BUT MAINTAINED THE
COOL PREVIOUS FORECAST FOR OTHER AREAS.
TES
DISCUSSION
/319 PM CST FRI NOV 20 2009/
CLOUDS CONTINUE TO STREAM N-NEWD INTO MAINLY THE SRN HALF OF MO
AHEAD OF THE MID-UPPER LEVEL TROF OVER TX. LIGHT RAIN MOVING NEWD
INTO SWRN MO BUT IT APPEARS THAT MOST OF THIS RAIN WILL REMAIN S
OF THE CWA. SHOULD BE INCREASING CLOUD COVER THOUGH TGT INTO SAT
AS MODELS BRING LOW LEVEL MOISTURE CENTERED AROUND 850 MB IN
HEIGHT NWD. DESPITE INCREASING CLOUD COVER AND PLENTY OF DAYTIME
HEATING AND MIXING TDA ACROSS MOST OF THE CWA THERE SHOULD STILL
BE AT LEAST PATCHY FOG DEVELOPING LATE TGT. THE FOG SHOULD NOT BE
AS WIDESPREAD OR AS DENSE AS LAST NGT. LOW TEMPERATURES SHOULD
ALSO NOT BE QUITE AS COLD AS WELL. RAIN SHOULD REMAIN S OF THE CWA
THIS WEEKEND AS THE SRN MID-UPPER LEVEL TROF MOVES EWD THRU THE
GULF COAST REGION. THERE WILL ALSO BE A WEAKER MID-UPPER LEVEL TROF
WHICH WILL MOVE EWD THRU THE GREAT LAKES AND OHIO VALLEY REGIONS.
MAIN SFC RIDGE WILL BE CENTERED E OF THE CWA WITH MAINLY SELY SFC
WINDS THIS WEEKEND. HIGH TEMPERATURES WILL BE SIMILAR TO TODAY AND
ABOVE SEASONAL NORMALS. NAM MODEL GENERATES QPF OVER THE SERN HALF
OF THE CWA SUN NGT AHEAD OF A WEAK SHRTWV MOVING EWD THRU THE REGION
AND N OF A WEAK SFC LOW MOVING NWD THRU ERN AR. DISCOUNTED THIS AS
NO OTHER MODEL FITS THIS SOLUTION NOR DOES THE PREVIOUS NAM MODEL
RUNS GENERATE THIS RAIN SUN NGT. NEXT CHANCE OF RAIN SHOULD OCCUR
MON NGT AND TUE AS A STRONG MID-UPPER LEVEL TROF/LOW AND ASSOCIATED
CDFNT/SFC LOW MOVE EWD THRU THE REGION. STILL A LOT OF MODEL
UNCERTAINTY WITH THE POSITION OF THE UPPER LEVEL AND ASSOCIATED SFC
LOW AND HOW PROGRESSIVE THIS SYSTEM WILL BE. THE GFS MODEL CONTINUES
TO BE MORE PROGRESSIVE AND FURTHER N WITH THIS SYSTEM WHILE THE
ECMWF IS SLOWER AND FURTHER S. FOR NOW JUST INCLUDED CHANCE POPS FOR
MON NGT AND TUE...WITH COLDER TEMPERATURES FOR WED AND THU.
GKS
AVIATION
/550 PM CST FRI NOV 20 2009/
FOR THE 00Z TAFS...MVFR CIGS FINALLY DISSIPATED/MOVED AWAY FROM
KUIN. IN THE MEANTIME...SC STARTING TO DEVELOP OVER SOUTHERN HALF OF
MISSOURI...WITH SOME CIRRUS BLANKETING THE AREA AS WELL. COVERAGE OF
THESE CLOUDS WILL DETERMINE FOG DEVELOPMENT FOR TONIGHT. FOR NOW
CONSIDERABLE MOISTURE REMAINS IN THE LOWER LEVELS AND THE FLOW IS
WEAK...GENERALLY A GOOD RECIPE FOR LOW STRATUS/FOG. SO KEPT PREVIOUS
FORECAST TO INDICATE THERE WILL BE SOME COOLING AND LOWERING
CIGS/VSYBS INTO IFR CAT DURING THE PREDAWN HOURS...BEFORE IMPROVING
DURING THE DAY ON SATURDAY.
BYRD
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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