542
FXUS63 KLSX 050103
AFDLSX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
803 PM CDT SAT JUL 4 2009
UPDATE
/803 PM CDT SAT JUL 4 2009/
PERSISTENT SHRA/TSRA REMAIN NEAR THE CDFNT/WRMFNT SYSTEM THAT IS
DRAPED OVER THE FA AND ALONG WITH THE LO PRES THAT IS LOCATED ENE
OF KCOU. THIS WILL TAKE MUCH OF THE EVENING AND PERHAPS EVEN THE
EARLY OVERNIGHT TO FULLY EXIT THE FA...AND IN LIGHT OF THESE
TRENDS ALSO OBSERVED ON RADAR...HAVE EXTENDED THE SCT/ISOLD RAIN
PROBS THRU MUCH OF THE NIGHT.
TES
DISCUSSION
/326 PM CDT SAT JUL 4 2009/
THE REMNANTS OF THE MCS FROM EARLIER TODAY HAVE WEAKENED AND
MOVED EAST LEAVING A RESIDUAL BNDRY DRAPED ACROSS SOUTHEAST/EAST
CENTRAL MISSOURI...WHILE THE SYNOPTIC SCALE CDFNT STILL REMAINS
WEST OF THE CWA WITH THE SFC LOW IN NW MO AND WARM FRONT EXTENDING
INTO CENTRAL IL. CLOUDS AND PCPN HOWEVER HAVE STABILIZED THE AIR
MASS QUITE A BIT IN THE WAKE OF THE MCS AND ONLY SWRN FRINGES OF
THE CWA AND NW MO HAVE SHOWN MUCH RECOVERY. LARGE SCALE ASCENT
ASSOCIATED WITH THE SHORT WAVE TROF NOW MOVING INTO ERN MO HAS
ALSO SPREAD INTO FAR SE MO AND SRN IL...WITH WEAK SUBSIDENCE
BEGINNING TO OVERSPREAD MUCH OF THE CWA IN ITS WAKE. SO THE BIG
QUESTION FOR THIS EVENING IS WHAT IS THE REMAINING PCPN THREAT AS
THE COLD FRONT MOVES SOUTHEAST ACROSS THE AREA. WHILE THE AIR MASS
ACROSS THE AREA STILL HAS SOME TIME FOR RECOVERY...THE WEAK LARGE
SCALE SUBSIDENCE DOES NOT BODE WELL FOR PRECIPITATION COVERAGE.
CURRENT THOUGHT IS THAT THE THREAT REMAINS FOR ISOLATED TO
SCATTERED SHOWERS AND THUNDERSTORMS THROUGH MAINLY THE FIRST PART
OF THE EVENING...ASSOCIATED WITH WEAK BOUNDARY LAYER
CONVERGENCE...AND MAINLY ACROSS THE SRN PART OF THE CWA.
THERE IS ALREADY QUITE A BIT OF CLOUDINESS AND THIS DOESN'T LOOK
LIKE IT WILL CHANGE SOON WHEN VIEWING THE AMOUNT OF STRATUS IN THE
WAKE OF THE COLD FRONT. THIS CLOUD COVER SHOULD ADVECT INTO THE
AREA TONIGHT...WITH OVERCAST SKIES EXPECTED AT DAYBREAK ON SUNDAY.
THIS CLOUD COVER SHOULD SLOWLY CLEAR FROM THE NORTH ON SUNDAY WITH
SE MO AND SRN IL NOT SEEING MUCH SUNSHINE UNTIL THE AFTERNOON. THE
COMBO OF THE CLOUDS AND NELY LOW LEVEL FLOW WILL RESULT IN ANOTHER
DAY OF COOL TEMPS BY JULY STANDARDS. HIGH PRESSURE WILL THEN
DOMINATE THE AREA SUNDAY NIGHT INTO MONDAY WITH TEMPS REMAINING BLO
NORMAL. MODERATION SHOULD GET UNDERWAY ON TUESDAY AS THE LOW LEVEL
ANTICYCLONE RETREATS AND A MORE SLY WIND COMPONENT AND WAA DEVELOP.
THE UPPER RIDGE ANCHORED OVER THE DESERT SOUTHWEST IS FORECAST TO
BUILD EASTWARD THROUGH THE SOUTHERN PLAINS AND INTO THE LOWER AND
MIDDLE MISSISSIPPI VALLEY REGION DURING THE LATER HALF OF THE
UPCOMING WEEK. THIS SHOULD RESULT IN A SEVERAL DAY PERIOD OF HEAT
MORE TYPICAL OF JULY WITH HIGHS WELL INTO THE 90S. INTERESTINGLY THE
GFS ENSEMBLE MEAN HAS WARMER H85 TEMPS THAN BOTH THE OPERATIONAL GFS
AND ECMWF DURING THIS PERIOD. HOW LONG THE HEAT WILL STAY IS A BIT
IN QUESTION. THE LATEST GUIDANCE IS SUGGESTING THE LONGEVITY OF THE
EASTWARD EXTENSION OF THE RIDGE AND ASSOCIATED HEAT WILL BE SOMEWHAT
SHORT-LIVED...WITH AN UPPER TROF DEVELOPING IN THE EASTERN U.S. AND
NW FLOW ALOFT/A COLD FROPA ACROSS OUR AREA LATE FRIDAY/EARLY SAT.
ATTM INTRODUCED SOME SLIGHT CHANCE POPS DURING THIS TIME FRAME AND
LOWER TEMPS INTO SATURDAY.
GLASS
AVIATION
/621 PM CDT SAT JUL 4 2009/
FOR THE 00Z TAFS...NEXT COUPLE OF HOURS WILL BE DIFFICULT TO PIN
DOWN THE SPECIFICS. GENERALLY...VFR CONDITIONS WILL CONTINUE AT
ALL TERMINALS EXCEPT FOR UIN. AT THESE OTHER SITES...EXPECT LINE
OF SHRA WITH ISO TSRA TO MOVE INTO THE AREA BY 03Z. BEHIND THIS
LINE CIGS WILL DROP DRAMATICALLY WITH CIGS POSSIBLY BRIEFLY AS LOW
AS BKN004. CIGS ARE EXPECTED TO REMAIN IN THE IFR RANGE OVERNIGHT.
SOME 5SM BR WILL LIKELY DEVELOP AS MOIST BOUNDARY LAYER COOLS. UIN
AND COU WILL LIKELY STAY ABOVE 6SM AS DRIER AIR WILL ADVECT INTO
THE AREA SOONER. AFTER SUNRISE...CIGS WILL GRADUALLY IMPROVE AS
SURFACE LOW PULLS EWD AND SOLAR INSOLATION HELPS BREAK UP CLOUDS.
ALL SITES SHUD BE VFR AROUND 18Z SUNDAY.
TILLY
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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