Severe Thunderstorm Warning 82, NWS St. Louis, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
300 AM CDT WED APR 19 2000

MAIN FORECAST CONCERN DEALS WITH THUNDERSTORM THREAT THROUGH THURSDAY.
00Z RUNS OF THE ETA AND NGM SEEM TO BE VERIFYING WELL AT 06Z.  PER
NCEP DISCUSSIONS...AVN SEEMS TO BE HAVING SIGNIFICANT PROBLEMS...SO
WILL FOLLOW OTHER TWO MODELS FOR THIS PACKAGE.

FIRST CONCERN DEALS WITH AMOUNT OF CLOUD COVER FOR TODAY.  00Z 850MB
UPR ANALYSIS SHOWED MID TEEN DEWPOINTS BEING ADVECTED NWD AHEAD OF
SYSTEM EJECTING OUT OF THE ROCKIES. SATELLITE TRENDS SHOWING SOME
PATCHY BKN CU DEVELOPING OVER MO ATTM...BUT NO MID OR HIGH CLOUDS.
THINK SOME AREAS WILL HAVE BKN/OVC CU INITIALLY...BUT GO SCT AS
INSTABILITY AND MIXING TAKE OVER.  WITH APRIL SUNSHINE...BREEZY SLY
WINDS AND +13 TO +16C 850 MB TEMPS...WILL GO A CAT ABOVE GUIDANCE
FOR HIGHS TODAY.

MORE SIGNIFICANT CONCERN IS THUNDERSTORM THREAT PER SPC SWODY1. 06Z
SFC ANALYSIS PLACED SFC LOW OVER SRN NEB WITH A DRY LINE EXTENDING
SWD INTO THE TX PANHANDLE AND A WARM FNT EWD THRU NRN MO INTO W
CNTRL IL. AREA OF TSRA IS STAYING JUST NORTH LSX CWFA ATTM WHERE LOW
LEVEL JET IS INTERSECTING WARM FRONT.  BOTH ETA AND NGM IS SHOWING
SOME MODEST SFC MOISTURE CONVERGENCE AND MID LEVEL UVV THROUGHOUT
THE CWFA TODAY...SO WILL USE CHC POP.  BETTER CHANCE WILL OCCUR AS
DRY LINE MOVES INTO WRN MO BY THIS EVENING AND MOVES THRU THE STATE
TONIGHT.  MOISTURE CONVERGENCE ALONG FRONT...700-500 UVV AND DOUBLE
JET STRUCTURE WILL SUPPORT LIKELY POPS TONIGHT IN MOST AREAS.
SBCAPES IN EXCESS OF 2500 J/KG AND 0-6KM SHEAR IN EXCESS OF 50 KTS
SHOULD SUPPORT SCT SVR TSRA LATE THIS AFTERNOON/EVENING OVER WRN
CWFA.  STORMS WILL LIKELY CONSOLIDATE INTO A LINE BY LATE EVENING...
BUT STEEP LAPSE RATES AND STRONG SHEAR SHOULD CONTINUE SVR THREAT
INTO ERN MO OVERNIGHT. WILL MENTION THREAT ACCORDINGLY IN ZONES.

SFC LOW AND FNT WILL REACH THE MS RIVER BY LATE MORNING TOMORROW...
SO BEST CHANCES OF SHRA/TSRA WILL BE IN IL.  EXPECT EXTENSIVE AREA
OF WRAP AROUND CLOUDS OVER NERN MO AND W CNTRL IL BEHIND LOW THU
AFTN.  850-700MB FRONTOGENTICAL FORCING AND PLACEMENT OF UPR LOW
WOULD SUPPORT CONTINUED CHC SHRA IN THIS AREA.

WILL CONTINUE TO LEAN TOWARD FWC TEMP GUIDANCE THRU PERIOD BASED ON
PREFERRING ETA/NGM SFC FEATURES BETTER THAN AVN.

.STL...NONE

BRITT

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-201200-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ST LOUIS MO
1140 AM CDT WED APR 19 2000

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
TONIGHT ALONG AND WEST OF A LINE FROM WHITE HALL ILLINOIS TO
ST LOUIS MISSOURI TO WEST PLAINS MISSOURI.  THERE IS A SLIGHT RISK TO
THE EAST OF THIS LINE.

SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG A COLD FRONT OVER
WESTERN MISSOURI LATE THIS AFTERNOON AND MOVE EAST.  THESE STORMS ARE
EXPECTED TO SPREAD INTO CENTRAL AND NORTHEAST MISSOURI TOWARD EARLY
EVENING...AND THEN INTO EAST CENTRAL MISSOURI AND SOUTHWEST ILLINOIS
LATER IN THE EVENING AND OVERNIGHT.  THE PRIMARY THREAT WITH THESE
STORMS WILL BE LARGE HAIL AND DAMAGING WINDS...THOUGH ISOLATED
TORNADOES ARE POSSIBLE.

THUNDERSTORM MOVEMENT WILL BE TO THE NORTHEAST AT 40 TO 50 MPH.

SPOTTER ACTIVATION WILL LIKELY BE NEEDED BEGINNING LATE THIS
AFTERNOON OVER CENTRAL AND NORTHEAST MISSOURI AND OVER EAST CENTRAL
MISSOURI AND SOUTHWEST ILLINOIS TONIGHT.

THIS OUTLOOK COVERS THE COUNTY WARNING AREA OF THE NATIONAL WEATHER
SERVICE OFFICE IN ST LOUIS.  AREAS INCLUDED ARE PORTIONS OF CENTRAL
AND EASTERN MISSOURI AS WELL AS SOUTHWEST ILLINOIS.

TES/JPK