Severe Thunderstorm Warning 250, NWS St. Louis, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
350 PM CDT WED AUG 20 2003

.DISCUSSION...
MAIN CHALLENGES FOR THIS PACKAGE DEALS WITH WHAT TO WITH EXISTING
HEAT HEADLINES AND PRECIP CHANCES ASSOCIATED WITH FRONT MOVING
THROUGH MO/IL THURSDAY NIGHT.  MODELS SHOWING GENERAL AGREEMENT
THROUGH THE EXTENDED PERIOD...SO USED A BLEND.

WILL UPGRADE TO A HEAT WARNING IN EXISTING ADVISORY AREA AND ISSUED
HEAT ADVISORY IN S CNTRL IL THROUGH THURSDAY.  MAY SEE A FEW MORE
CLOUDS ACROSS THE AREA TOMORROW...BUT 850MB TEMPS WILL STILL BE IN
THE LOW 20S C WITH W-SWLY LOW LEVEL FLOW SHOULD STILL YIELD SFC
TEMPS IN THE MID 90S.  MODELS STILL KEEPING DEWPOINTS IN THE LOW-MID
90S...YIELDING HEAT INDEX VALUES AOA 105F FOR A FEW AREAS
TOMORROW...SO THIS WILL BE THE 3RD CONSECUTIVE DAY OR LONGER
ELEVATING THE HEALTH RISK ACROSS MOST OF THE AREA.

REGIONAL RADARS SHOWING RAPID TSRA DEVELOPMENT OVER ERN MO AND SW IA
IN AREA OF WEAK LOW LEVEL MOISTURE CONVERGENCE COINCIDING WITH VERY
UNSTABLE/LOW CINH ATMOSPHERE.  SOME WEAK UPWARD MOTION AHEAD OF
SHORTWAVE TROUGH OVER MID MO RIVER VALLEY WILL AID IN THIS
DEVELOPMENT...SO HAVE SCT TSRA GOING THROUGHOUT THE EVENING OVER WRN
2/3RDS OF AREA.

OTHERWISE...WILL KEEP CHANCE OF TSRA GOING WITH FRONTAL BOUNDARY
MOVING SLOWING THROUGH AREA ON THURSDAY NIGHT/EARLY FRIDAY AS
SHORTWAVE TROUGH MOVES THROUGH AREA.  MID-UPPER LEVEL SUPPORT IS
PRETTY MEAGER...SO KEPT COVERAGE SCT.

IN THE EXTENDED...STRONG WESTERLIES ARE PUSHED BACK NORTHWARD EARLY
NEXT WEEK LEAVING AREA WARM AND DRY.

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
.MO...EXCESSIVE HEAT WARNING THROUGH THURSDAY
.IL...EXCESSIVE HEAT WARNING FOR SW AND W CNTRL IL...AND HEAT
ADVISORY FOR S CNTRL IL THROUGH THURSDAY

BRITT

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-211200-

HAZARDOUS WEATHER OUTLOOK...UPDATED FOR SLIGHT CHANCE SEVERE STORMS
NATIONAL WEATHER SERVICE ST LOUIS MO
1240 AM CDT WED AUG 20 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL AND EASTERN MISSOURI
AND WEST CENTRAL AND SOUTHWEST ILLINOIS.

.DAY ONE...TODAY AND TONIGHT
A HEAT ADVISORY IS IN EFFECT TODAY OVER ALMOST THE ENTIRE REGION...
GENERALLY WEST OF A LINE FROM 60 MILES NORTHEAST OF ST LOUIS
SOUTHWARD TO 70 MILES SOUTHEAST OF ST LOUIS. MAXIMUM TEMPERATURES
TODAY WILL BE IN THE MIDDLE 90S NEAR THE MISSISSIPPI RIVER UPWARD
TO 100 DEGREES ACROSS CENTRAL MISSOURI.  ABOVE NORMAL TEMPERATURES
COMBINED WITH VERY HUMID CONDITIONS WILL PRODUCE DANGEROUSLY HIGH
HEAT INDICES OF AROUND 105 TO 110 DURING THE AFTERNOON HOURS.  AN
EXCESSIVE HEAT WARNING IS ALSO IN EFFECT FOR THE CITY OF ST LOUIS AS
TEMPERATURES AND HEAT INDICES COULD BE SLIGHTLY HIGHER THROUGHOUT
THE URBAN AREAS IN AND AROUND THE METRO ST LOUIS AREA.

THERE IS A CHANCE OF THUNDERSTORMS ACROSS THE REGION THIS AFTERNOON
AND TONIGHT...MAINLY NORTH AND WEST OF ST LOUIS.  HOWEVER...THERE
WILL BE A SLIGHT RISK THAT SOME OF THESE THUNDERSTORMS COULD BECOME
SEVERE. ISOLATED STORMS COULD PRODUCE A BRIEF PERIOD OF HAIL
...HOWEVER THE MAIN THREAT WILL DUE TO STRONG OR POSSIBLY DAMAGING
WIND GUSTS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THERE IS A CHANCE FOR THUNDERSTORMS THURSDAY THROUGH FRIDAY NIGHT
AS A COLD FRONT MOVES SLOWLY SOUTHEAST THROUGH THE REGION.  WHILE
WIDESPREAD SEVERE THUNDERSTORMS ARE NOT EXPECTED ALONG THIS FRONT...
ISOLATED STORMS MAY PRODUCE A BRIEF PERIOD OF HAIL OR STRONG WIND
GUSTS.

.SPOTTER ACTIVATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATE THIS AFTERNOON AND EVENING
IN NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS.

&&

MORE INFORMATION MAY BE OBTAINED AT...
HTTP://WWW.CRH.NOAA.GOV/LSX (ALL LOWER CASE)

PEDIGO