Severe Thunderstorm Warning 204, NWS St. Louis, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
238 PM CDT TUE AUG 10 2010

.DISCUSSION...
/237 PM CDT TUE AUG 10 2010/

THE LIFE THREATENING HEAT CONTINUES TO BE THE MAIN STORY AS IT NOW LOOKS
LIKE IT WILL LAST UNTIL LATE FRIDAY. EACH ADDITIONAL DAY INCREASES THE
LIKELIHOOD OF HEAT RELATED INJURIES...SO WILL BE EXTENDING THE CURRENT
WARNING FOR THE ENTIRE CWA UNTIL FRIDAY EVENING.

LIKE YESTERDAY...WE HAD AN OUTFLOW BOUNDARY COME OUT OF IOWA THIS
MORNING AND MAKE IT SOUTH OF I-70...BUT SEVERAL OBS SITES TO THE
NORTH OF THE BOUNDARY HAD HEAT INDEX READINGS ABOVE 105 BY 10
AM...WITH HEAT INDICES IN THE 105 TO 120 DEGREE RANGE BY 1 PM.
THIS IS A VERY HUMID AIRMASS WITH DEWPOINTS IN THE 75-80 DEGREE RANGE
COVERING MOST OF THE AREA. DO NOT EXPECT MUCH CHANGE WITH THESE
HIGH READINGS THROUGH TOMORROW...THOUGH MODEL SOUNDINGS SHOW THAT
THERE MAY BE A BIT MORE MIXING OUT OF THE DEWPOINTS THURSDAY INTO
FRIDAY. AMBIENT TEMPERATURE WISE...THESE SOUNDINGS ALSO SHOW THAT
THE DEEP MIXING UP TO 800MB THROUGH FRIDAY WARRANT GOING WITH THE
WARMER MOS HIGHS IN THE UPPER 90S TO AROUND 100. RESULTING HEAT
INDICES ON WEDNESDAY WILL BE MUCH LIKE TODAY...WITH MANY SITES IN
THE AREA GOING ABOVE 110F. HEAT INDICES OVER MUCH OF THE AREA ON
THURSDAY AND NOW FRIDAY LOOK LIKE THEY WILL BE IN THE 105 TO 110
RANGE CAUSING THE NEED TO EXTEND THE WARNING AT THIS TIME.

SCT STORMS THAT HAVE DEVELOP THIS AFTERNOON LOOK TO BE FORCED BY
THE WEAK OUTFLOW FROM EARLIER OR OROGRAPHIC LIFT IN THE EASTERN
OZARKS. NAM/GFS IS CONSISTENT WITH LIFTING THE BOUNDARY THIS
EVENING...BUT THINK COVERAGE OF STORMS WILL BE ISOLD WITH LOSS OF
DAYTIME HEATING. MCS TRAIN ALSO LOOKS LIKE IT WILL STAY JUST NORTH
OF THE CWA. WILL KEEP CHANCE OF STORMS GOING OVER THE ERN HALF OF
THE CWA ON WEDNESDAY INTO THURSDAY WHICH THE NAM/GFS HAVE BEEN
CONSISTENT IN DEPICTING A WEAK BOUNDARY THAT WILL LIKE UNDER SOME
WEAK ASCENT PROVIDED BY A SHORTWAVE TROUGH ROUNDING THE TOP OF THE
RIDGE. THE LACK OF DEEP SHEAR SHOULD LIMIT SEVERE POTENTIAL...BUT
THE EXTREME INSTABILITY...PWATS AROUND 2.2 INCHES AND DEEP WARM
CLOUD LAYERS SHOULD CAUSE THESE STORMS TO BE EFFICIENT RAIN
PRODUCERS.

GFS/ECMWF HAVE GOOD CONTINUITY DEPICTING A FRONT MOVING THROUGH
MO/IL ON SATURDAY IN RESPONSE TO A STRONG SHORTWAVE TROUGH THAT IS
ROTATING THROUGH THE UPPER MIDWEST/GREAT LAKES ON THE SOUTH SIDE OF
AN INTENSE CANADIAN VORTEX. EXPECT STORMS ALONG THE FRONT FRIDAY
NIGHT/SATURDAY...AND THEN DRY INTO EARLY NEXT WEEK AS A STRONG
SURFACE HIGH BUILDS DOWN. THIS FRONT WILL BRING AN END TO THE
INTENSE HEAT AS TEMPS FALL BACK CLOSER TO NORMAL VALUES GIVEN
850MB TEMPS WILL DROP FROM AROUND 20C ON SATURDAY TO AROUND 16C ON
MONDAY AND TUESDAY.

BRITT

&&

.AVIATION...
/105 PM CDT TUE AUG 10 2010/

OUTFLOW MOVED THROUGH PORTIONS OF THE AREA IN THE PAST COUPLE OF
HOURS...WITH WINDS BRIEFLY SWITCHING TO THE NORTHEAST TO EAST...BUT
MOST SITES HAVE BECOME LIGHT AND VARIABLE OVERALL. OTHERWISE...ISSUE
CONTINUES TO BE POSSIBILITY OF ISOLATED STORMS NEAR TAF SITES THIS
AFTERNOON...BUT TRYING TO FIGURE OUT WHERE THEY WILL FIRE UP IS NEAR
IMPOSSIBLE. SO FOR NOW KEPT CB MENTION AT ALL TAF SITES THROUGH 01Z.

BY MID MORNING TOMORROW...SHOULD SEE WINDS PICKUP JUST A BIT FROM
THE SOUTH TO SOUTHWEST AROUND 06KTS...WITH DIURNAL CU DEVELOPING
ONCE AGAIN.

SPECIFICS FOR KSTL...SOME STORMS TRYING TO FIRE OVER METRO AREA AS
OF 18Z...BUT FOR NOW HAVE CB MENTION IN TAF...WILL KEEP AN EYE THEM
FOR UPDATES AS NEEDED. AS FOR WINDS...CURRENTLY HAVE AN EASTERLY
COMPONENT...WITH THEM EXPECTED TO BECOME A BIT MORE SOUTHEASTERLY
LATER THIS AFTERNOON...THEN BECOME LIGHT AND VARIABLE TOWARDS SUNSET.
BY MID MORNING TOMORROW...SHOULD SEE WINDS PICKUP JUST A BIT FROM
THE SOUTH TO SOUTHWEST AROUND 06KTS...WITH DIURNAL CU DEVELOPING
ONCE AGAIN AND ADDED CB MENTION BY 20Z.

BYRD

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...EXCESSIVE HEAT WARNING UNTIL 9 PM CDT FRIDAY FOR AUDRAIN MO-
     BOONE MO-CALLAWAY MO-COLE MO-CRAWFORD MO-FRANKLIN MO-
     GASCONADE MO-IRON MO-JEFFERSON MO-KNOX MO-LEWIS MO-LINCOLN
     MO-MADISON MO-MARION MO-MONITEAU MO-MONROE MO-MONTGOMERY MO-
     OSAGE MO-PIKE MO-RALLS MO-REYNOLDS MO-SHELBY MO-ST. CHARLES
     MO-ST. FRANCOIS MO-ST. LOUIS CITY MO-ST. LOUIS MO-STE.
     GENEVIEVE MO-WARREN MO-WASHINGTON MO.

IL...EXCESSIVE HEAT WARNING UNTIL 9 PM CDT FRIDAY FOR ADAMS IL-BOND
     IL-BROWN IL-CALHOUN IL-CLINTON IL-FAYETTE IL-GREENE IL-
     JERSEY IL-MACOUPIN IL-MADISON IL-MARION IL-MONROE IL-
     MONTGOMERY IL-PIKE IL-RANDOLPH IL-ST. CLAIR IL-WASHINGTON
     IL.

&&

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
351 PM CDT TUE AUG 10 2010

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-111215-
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-
351 PM CDT TUE AUG 10 2010

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

.DAY ONE...TONIGHT

DANGEROUS HEAT INDICES WILL SLOWLY FALL TO BELOW 100 DEGREES DURING
THE EVENING HOURS. LOW TEMPERATURES WILL ONLY FALL TO BETWEEN 75
AND 80 DEGREES PROVIDING LITTLE RELIEF FROM THE HEAT. AN EXCESSIVE
HEAT WARNING REMAINS IN EFFECT.

SCATTERED THUNDERSTORMS WILL CONTINUE TO PRODUCE VERY HEAVY DOWNPOURS
WHICH COULD CAUSE LOCALIZED FLOODING OF LOW LYING AREAS THROUGH EARLY
EVENING. THE STRONGEST STORMS WILL ALSO BE CAPABLE OF PRODUCING
WIND GUSTS IN EXCESS OF 40 MPH.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THE LIFE THREATENING HEAT WILL CONTINUE THROUGH FRIDAY EVENING
WITH PEAK HEAT INDEX VALUES IN THE 105 TO 120 DEGREE RANGE DURING
THE AFTERNOON AND EARLY EVENING HOURS EACH DAY. EXPECT LITTLE
RELIEF FROM THE HEAT AT NIGHT AS TEMPERATURES ONLY FALL TO BETWEEN
75 AND 80 DEGREES. THE EXCESSIVE HEAT WARNING WILL REMAIN IN
EFFECT UNTIL FRIDAY EVENING AT 9 PM.

THERE IS A CHANCE FOR THUNDERSTORMS OVER PARTS OF THE AREA FROM WEDNESDAY
THROUGH THURSDAY...AND ALSO FROM FRIDAY NIGHT INTO SATURDAY NIGHT.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED ON A LIMITED BASIS THROUGH THIS
EVENING.

&&

FOR A GRAPHICAL VERSION OF THIS INFORMATION SEE OUR
WEBPAGE AT (LOWERCASE)... HTTP://WWW.WEATHER.GOV/LSX/?N=HWO1

BRITT

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ST LOUIS MO
355 PM CDT TUE AUG 10 2010

MOZ061-102145-
ST. CHARLES MO-
355 PM CDT TUE AUG 10 2010

...SIGNIFICANT WEATHER ADVISORY FOR CENTRAL ST. CHARLES COUNTY UNTIL
445 PM CDT...

AT 348 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM BETWEEN O'FALLON AND ST. PETERS...MOVING NORTH
AT 5 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THIS STORM...ALONG WITH HEAVY RAIN.

LOCATIONS NEAR THE PATH OF THIS STORM INCLUDE...
  ST. PAUL...
  KAMPVILLE...

IF THREATENING WEATHER APPROACHES YOUR AREA...TAKE SHELTER IN A
STURDY BUILDING.

TORRENTIAL RAIN...WHICH MAY FLOOD LOW LYING AREAS SUCH AS DITCHES AND
UNDERPASSES...IS ALSO LIKELY. DO NOT DRIVE YOUR VEHICLE ON A FLOODED
ROADWAY.

BYRD

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ST LOUIS MO
401 PM CDT TUE AUG 10 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0359 PM     HAIL             O'FALLON                38.78N  90.71W
08/10/2010  E0.50 INCH       ST. CHARLES        MO   LAW ENFORCEMENT

            HAIL OBSERVED OUTSIDE THE SHERIFF OFFICE ON TOM
            GINNEVER AVENUE

&&

JP

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ST LOUIS MO
409 PM CDT TUE AUG 10 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0406 PM     HEAVY RAIN       ST. PETERS              38.78N  90.61W
08/10/2010  M1.70 INCH       ST. CHARLES        MO   NWS EMPLOYEE

&&

JP

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