River Flood Warning 117, NWS St. Louis, MO

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
952 PM CDT SAT MAY 21 2011

.UPDATE...
/946 PM CDT SAT MAY 21 2011/

THUNDERSTORMS CONTINUE TO BACKBUILD ACROSS NW MO INTO NE KS IN
RESPONSE TO LIFT VIA A 35+ SWLY LLJ AND RESERVIOR OF HIGH CAPE
AIR ACROSS EASTERN KS. LEADING EDGE OF THE ELONGATING NE-SW
ORIENTED THUNDERSTORM CLUSTER IS GENERALLY TRACKING NEWD IN GOOD
AGREEMENT WITH FORWARD PROPAGATING CFM VECTORS. THE LLJ SHOULD
CONTINUE TO GRADUALLY VEER AS THE NIGHT PROGRESSES AND THIS SHOULD
RESULT IN SAME OVERALL RADAR TRENDS NOTED IN THE LAST FEW HOURS
WITH GREATEST THREAT OF THUNDERSTORMS ACROSS THE NORTHERN TIER OR
TWO OF COUNTIES IN THE CWA...ACROSS NE MO AND INTO WEST CENTRAL
IL. LAST 3-4 RUNS OF HRRR SUPPORT THIS SCENARIO AS WELL. THE OVERALL
SEVERE THREAT ON LEADING EDGE IS DIMINISHING AND SEE NO REASON WHY
THIS SHOULD CHANGE AS STORMS MOVE INTO LESSER CAPE VALUES FROM NE
MO INTO WEST CENTRAL IL.

GLASS

&&

.DISCUSSION...
/256 PM CDT SAT MAY 21 2011/

MAIN FORECAST CONCERN IS THE POTENTIAL FOR SEVERE WEATHER AND
SIGNIFICANT RAINFALL INTO THE MIDDLE OF NEXT WEEK.

DRY WEATHER HAS BEEN THE RULE TODAY AS INSTABILITY IS ONLY NOW
INCREASING IN WAKE OF THE SHORTWAVE TROUGH THAT MOVED THROUGH
MO/IL LAST NIGHT. LATEST RUNS OF THE RUC AND HRRR OF BEEN
CONSISTENT IN SUGGESTING THUNDERSTORMS WILL DEVELOP OVER NORTHWEST
MISSOURI LATER THIS AFTERNOON/EARLY EVENING AS CENTRAL PLAINS
SHORTWAVE MOVES OVER AXIS OF INCREASING INSTABILITY. IF THESE
STORMS DO DEVELOP THEY WILL LIKELY ORGANIZE INTO A MCS AND MOVE
EASTWARD ACROSS NORTHERN MO LATER THIS EVENING. ELSEWHERE...ONLY
HAVE SLIGHT CHANCE OF THUNDERSTORMS GOING OWING TO A LACK OF ANY
NOTABLE FORCING. ANY STORMS IN THE CWA WILL HAVE SOME POTENTIAL
TO BE SEVERE GIVEN THE DEEP SHEAR OF 30-40KTS AND MUCAPES BETWEEN
1000-2500 J/KG.

FEEL THAT BETTER CHANCE FOR THUNDERSTORMS WILL COME LATE SUNDAY INTO
SUNDAY NIGHT WHEN A SLIGHTLY STRONGER SHORTWAVE TROUGH MOVES ACROSS
MO/IL.  THIS WILL BRING A COLD FRONT INTO NORTHERN MO AND WEST
CENTRAL IL WHERE I HAVE THE HIGHEST CHANCE POPS.  GFS/NAM ARE
SHOWING SOME INCREASE 925-850MB OVER THE WARM SECTOR WHICH COULD
ALSO INTI ATE CONVECTION OVER THE AREA.  DO EXPECT MUCAPES TO BE
2000-3000+ J/KG WITH SLIGHTLY HIGHER DEEP LAYER SHEAR VALUES
ALLOWING FOR AN INCREASED RISK FOR SEVERE WEATHER. MODELS ARE THEN
IN DECENT AGREEMENT THAT THE CENTRAL CONUS WILL REMAIN UNDER ZONAL
FLOW THROUGH THE MIDDLE OF NEXT WEEK WITH THE AFOREMENTIONED
FRONTAL BOUNDARY BECOMING EAST-WEST ORIENTED WHICH IS TYPICAL FOR
LATE MAY INTO EARLY JUNE. UNFORTUNATELY THIS PATTEN ALSO TENDS TO
BRING THE RISK FOR SEVERE WEATHER IN ADDITION TO THE THREAT FOR
HEAVY RAINFALL AS THERE WILL BE A SERIES OF SHORTWAVE STORM
SYSTEMS ACROSS THE STATIONARY FRONT WITH PWATS OF 1.50+ INCHES.
WILL CONTINUE TO WATCH EVOLUTION OF MODEL SOLUTIONS THE NEXT FEW
DAYS AS THIS MORNINGS HPC QPF GUIDANCE SHOWED THE POTENTIAL FOR
3-5+ INCHES OF RAINFALL OVER THE CWA THROUGH WEDNESDAY.

GFS AND ECMWF ARE BOTH SHOWING A CLOSED LOW OVER THE CENTRAL PLAINS
THAT WILL SLOWLY MIGRATE EASTWARD ACROSS THE MIDDLE MISSISSIPPI
VALLEY ON FRIDAY. BASED ON THIS...WILL KEEP HIGH CHANCES FOR RAIN
GOING THROUGH AT LEAST THURSDAY WITH BELOW NORMAL TEMPERATURES.
CHANCES OF RAIN MAY LINGER FRIDAY AND SATURDAY...BUT WITH
INCREASING SPREAD IN MODEL SOLUTIONS HAVE KEPT FORECAST DRY AT
THIS POINT.

BRITT

&&

.AVIATION...
/653 PM CDT SAT MAY 21 2011/

PRIMARY CONCERN FOR AVIATION INTERESTS THE NEXT 24 HOURS WILL BE
THE CHANCE FOR THUNDERSTORMS. LATEST MODEL GUIDANCE INDICATES THAT
STORMS OVER EASTERN KANSAS AND WESTERN MISSOURI WILL MOVE ACROSS
NORTHERN MISSOURI AND SOUTHERN IOWA...POTENTIALLY GRAZING THE KUIN
TAF SITE. STILL SOME CHANCE THAT ADDITIONAL DEVELOPMENT MAY AFFECT
PARTS OF CENTRAL MISSOURI DURING THE EVENING...THOUGH THIS IS
LOOKING LESS LIKELY THAN IT WAS EARLIER. ADDITIONALLY...SOME
SHOWERS MAY ALSO AFFECT PARTS OF SOUTHEAST MISSOURI DURING THE
EVENING HOURS. VFR CONDITIONS WILL OTHERWISE PREVAIL OUTSIDE OF STORMS.

THE FRONT WHICH IS CAUSING THE STORMS TO FIRE IN KANSAS WILL DRIFT
FURTHER EAST INTO MISSOURI ON SUNDAY WHICH WILL INCREASE CHANCES
FOR THUNDERSTORMS DURING THE AFTERNOON. TIMING AND AREAL EXTENT OF
STORMS IS AS YET UNCERTAIN. ELSEWHERE AND OTHERWISE...SOUTHWEST
FLOW GUSTING TO 25-30KTS AND VFR CONDITIONS WILL PREVAIL OUTSIDE
OF ACTIVE CONVECTION.

SPECIFICS FOR KSTL...

VFR FLIGHT CONDITIONS AND SOUTHERLY FLOW WILL PREVAIL AT LAMBERT
TONIGHT. THERE IS STILL A SMALL CHANCE THAT A THUNDERSTORM WILL
AFFECT THE AIRPORT TONIGHT...THOUGH IT LOOKS LIKE MOST OF THE
CONVECTION WILL PASS WELL NORTH OF THE TERMINAL. WIND WILL VEER
SLIGHTLY TO THE SOUTHWEST AND BECOME GUSTY ON SUNDAY MORNING...AND
THE CHANCE FOR THUNDERSTORMS WILL INCREASE DURING THE AFTERNOON AS
THE COLD FRONT MOVES INTO PARTS OF WESTERN AND CENTRAL MISSOURI.

CARNEY

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
333 PM CDT SAT MAY 21 2011

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-221200-
GREENE IL-MACOUPIN IL-MONTGOMERY IL-BOND IL-FAYETTE IL-CLINTON IL-
MARION IL-WASHINGTON IL-RANDOLPH IL-ADAMS IL-BROWN IL-PIKE IL-
CALHOUN IL-JERSEY IL-MADISON IL-ST. CLAIR IL-MONROE IL-KNOX MO-
LEWIS MO-SHELBY MO-MARION MO-MONROE MO-RALLS MO-PIKE MO-BOONE MO-
AUDRAIN MO-MONITEAU MO-COLE MO-OSAGE MO-CALLAWAY MO-MONTGOMERY MO-
LINCOLN MO-GASCONADE MO-WARREN MO-ST. CHARLES MO-FRANKLIN MO-
ST. LOUIS MO-ST. LOUIS CITY MO-JEFFERSON MO-CRAWFORD MO-
WASHINGTON MO-ST. FRANCOIS MO-STE. GENEVIEVE MO-IRON MO-
MADISON MO-REYNOLDS MO-
333 PM CDT SAT MAY 21 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN AND
CENTRAL MISSOURI AS WELL AS WEST CENTRAL AND SOUTHWEST ILLINOIS.

.DAY ONE...TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS OVER THE REGION TONIGHT. A FEW
OF THUNDERSTORMS COULD BE SEVERE MAINLY ALONG AND WEST OF THE
MISSISSIPPI RIVER. THE STRONGEST STORMS WILL BE CAPABLE OF
PRODUCING LARGE HAIL AND DAMAGING WINDS.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THE CHANCE OF THUNDERSTORMS WILL CONTINUE OVER THE REGION FROM
SUNDAY INTO THURSDAY NIGHT. THERE WILL CONTINUE TO BE A RISK OF
SEVERE THUNDERSTORMS THROUGH MONDAY NIGHT. IN ADDITION...
WIDESPREAD RAINFALL...POSSIBLY HEAVY...MAY CAUSE RISES ON AREA
STREAMS...CREEKS AND RIVERS EARLY NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT.

BRITT