000
FXUS63 KLSX 080449
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1149 PM CDT SUN SEP 7 2008
.DISCUSSION...
/247 PM CDT SUN SEP 7 2008/
MAIN CONCERN THE NEXT FEW DAYS IS PRECIPITATION CHANCES AND THE
POTENTIAL FOR SEVERE WEATHER TOMORROW. STILL WILL LEAN TOWARD THE
GFS AS IT`S SLIGHTLY WEAKER MID LEVEL TROUGH AND QUICKER SURFACE
FROPA TOMORROW AGREES BETTER WITH THE ECMWF/UKMET AND HAS BETTER RUN
TO RUN CONTINUITY THAN THE NAM.
HAVE KEPT CHANCE OF TSRA OVER THE WRN HALF OF THE CWA BEGINNING
LATE THIS EVENING AS STRIPE OF 925-850MB MOISTURE CONVERGENCE
PUSHES NWD ACROSS THE CWA ON NOSE OF BROAD LOW LEVEL JET THAT
EXTENDS WESTWARD INTO THE CENTRAL PLAINS. MUCAPES WILL INCREASE
INTO THE 500-1000 J/KG BY 12Z OVER CNTRL MO. BETTER CHANCE OF TSRA
WILL COME TOMORROW AS LARGE SCALE ASCENT INCREASES AHEAD OF
APPROACHING SHORTWAVE TROUGH AND AREA WILL LIE UNDER RIGHT
ENTRANCE REGION OF GREAT LAKES JET STREAK. GFS MLCAPES OF
1000-1500 J/KG OVER THE CNTRL AND SRN PART OF THE THE CWA LOOK
REASONABLE WITH DEEP LAYER SHEAR VALUES RANGING FROM 30KTS OVER
THE SRN PART OF THE CWA TO 50KTS OVER THE NORTH. BEST CHANCE FOR
ORGANIZED SEVERE WEATHER INCLUDING SUPERCELLS LOOKS LIKE IT WILL
BE OVER THE CNTRL AND NRN PART OF THE CWA WHERE THERE WILL BE THE
BEST COMBINATION OF INSTABILITY AND SHEAR. WILL KEEP LIKELY POPS
GOING BEHIND THE FRONT OVER THE NRN PART OF THE CWA TOMORROW
EVENING AS SYSTEM WILL HAVE A DECENT AMOUNT OF MID-LEVEL
FRONTOGENESIS. SUBSIDENCE WILL THEN KICK IN BEHIND SHORTWAVE
BRINGING A RETURN TO DRY WEATHER TUESDAY AND WEDNESDAY.
TEMPERATURES ARE A REFLECTION OF THE GFS MOS GUIDANCE BASED ON
PREFERENCE OF THE GFS.
BOTH THE GFS AND ECWMF ARE SHOWING SIGNIFICANT DIFFERENCES IN HOW
QUICKLY A TROUGH OVER WRN CONUS ON THURSDAY MORNING WILL MOVE
EASTWARD. THE ECWMF KEEPS THE TROUGH OVER THE ROCKIES LONGER AND
DOESN`T BRING IT ACROSS THE MID MS VALLEY UNTIL LATE SATURDAY/EARLY
NEXT SUNDAY COMPARED TO THE MORE PROGRESSIVE GFS WHICH BRINGS IT
ACROSS ABOUT A DAY EARLIER. COMPLICATING THINGS IS THAT EACH MODEL
EXHIBITS SIGNIFICANT CONTINUITY PROBLEMS AND THAT THERE IS NO
CONSENSUS AMONGST THE OTHER MEDIUM RANGE MODELS THAT FAVORS EITHER
ONE. DECIDED TO FOLLOW HPC GUIDANCE WHICH BRINGS A FRONT INTO THE
MID MS VALLEY ON FRIDAY AND STALLS IT OVER US NEXT WEEKEND AS IT
BECOMES ORIENTED TO THE UPPER FLOW. THIS REQUIRES LOWERING POPS ON
THURSDAY AND INCREASING POPS FRIDAY INTO SUNDAY. TEMPERATURES ARE
BASED ON HPC AND PERSISTENCE.
BRITT
&&
.AVIATION...
/1107 PM CDT SUN SEP 7 2008/
FOR THE 06Z TAFS...AREA OF LOWER CIGS ACROSS SRN MO SHUD CONTINUE
TO SPREAD NWD TONIGHT ALONG AXIS OF WAA. MODELS INDICATE THAT SOME
SHRA MAY DEVELOP ALONG THIS AXIS IN CENTRAL MO...BUT SHRA SHUD BE
SCT AT BEST. THESE CLOUDS SHUD HELP SUPPRESS FG DEVELOPMENT AT
SUS. VISBYS MAY DROP TO MVFR BUT SHUD ONLY BE FOR A SHORT TIME.
OTHERWISE...SOME MINOR TWEAKS FROM PREV TAFS AS LATEST MODELS
KEEP LOW SYSTEM A LITTLE FURTHER S. MONDAY AFTERNOON STILL LOOKS
THE BEST FOR CHANCES OF TSRA AT TAF SITES. GIVEN EXPECTED
ENVIRONMENT MONDAY AFTERNOON...EXPECT TSRA TO BE DISCRETE CELLS
BEFORE MERGING INTO A MORE LINEAR FORM. GIVEN UNCERTAINTIES WITH
INITIATION AND PLACEMENT...HAVE NOT MENTIONED TSRA IN TAFS OTHER
THAN VCNY.
TILLY
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&
$$
WFO LSX
