Issued by NWS St. Louis, MO
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000 FXUS63 KLSX 202350 AFDLSX AREA FORECAST DISCUSSION...UPDATED AVIATION NATIONAL WEATHER SERVICE ST LOUIS MO 550 PM CST FRI NOV 20 2009 .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