Severe Thunderstorm Warning 268, NWS St. Louis, MO

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
743 PM CDT SUN OCT 24 2010

.DISCUSSION...
/223 PM CDT SUN OCT 24 2010/

CONCERNS WITH THIS FCST PACKAGE INCLUDE CONVECTIVE POTENTIAL
TONIGHT...A STRONG COLD FRONT WITH A LINE OF STORMS MOVING THROUGH
TOMORROW NIGHT...GUSTY WINDS ON TUE...AND MUCH COOLER TEMPERATURES
TOWARDS THE END OF THE WEEK.

COMPLEX LOW PRESSURE SYSTEM OVER THE CENTRAL PLAINS CONTINUES TO
LIFT NEWD INTO THE GRTLKS REGION. AFTERNOON WATER VAPOR IMAGERY
SHOWED ANOTHER SHORTWAVE LOCATED OVER THE SOUTHERN PLAINS...AND IT
IS THIS FEATURES THAT WILL BE RESPONSIBLE FOR RENEWED SHRA/TSRA CHCS
TONIGHT. CLOUDS HAVE THINNED SOMEWHAT AND BECOME MORE
CUMULIFORM IN NATURE BASED ON SATELLITE IMAGERY AND A GLANCE OUT THE
WINDOW. SPC MESOANALYSIS GRAPHICS HAVE SHOWN INCREASING CAPE ACROSS
THE AREA...LIKELY DUE TO A COMBINATION OF INCREASING SFC MOISTURE
BEING TRANSPORTED NWD...INSOLATION IN LOCATIONS WHERE CLOUDS HAVE
STARTED TO DISSIPATE...AND FALLING TEMPERATURES ALOFT. SREF CAPE
PROBABILITIES HIGHLIGHT THE SERN HALF OF THE CWA FROM 21Z THROUGH
06Z. AREA VWP/PROFILER OBS ARE CONSISTENT WITH MODEL DEPICTIONS OF A
BROAD H85 LLJ THAT RAMPS UP TO 30-40 KTS DURING THE SAME TIME. GIVEN
APPROACHING SHORTWAVE TROF AND ABOVE FACTORS...MAINTAINED CHC POPS
AND INCREASED TO LIKELY ACROSS FAR ERN COUNTIES TO COVER EXPECTED
SHRA/TSRA DEVELOPMENT TONIGHT.

STILL LOOKS LIKE TOMORROW WILL BE DRY DURING THE DAY SINCE THE CWA
WILL BE LOCATED BETWEEN SYNOPTIC SYSTEMS. A STRONG LOW PRESSURE
SYSTEM BECOMES NEGATIVELY TILTED TOMORROW NIGHT AND IS EXPECTED TO
DRIVE A CDFNT THROUGH THE REGION. AS DEPICTED BY THE
MODELS...NOTABLE FEATURES WITH THIS SYSTEM INCLUDE A 50-60KT
LLJ...PW VALUES INCREASING TO 1.25 INCHES AHEAD OF THE COLD
FRONT...AND VERY STRONG SHEAR. THIS IS EXPECTED TO RESULT IN DVLPMT
OF A SQUALL LINE THAT MOVES RAPIDLY ACROSS THE CWA ON MON NIGHT INTO
TUE MORNING...AND SOME OF THE STORMS EMBEDDED IN THAT LINE MAY
PRODUCE SEVERE WEATHER. WINDS THEN INCREASE MARKEDLY BEHIND THE
FRONT ON TUE DUE TO THE TIGHT PRESSURE GRADIENT. ADDITIONALLY...CLRG
SKIES WILL PROMOTE GOOD MIXING AND LEAD TO STRONGER GUSTS MIXING
DOWN TO THE SURFACE. ATTM IT DOES NOT LOOK LIKE WE WILL MEET LOCAL
CRITERIA FOR A WIND ADVISORY /SUSTAINED WINDS OF 30-39 MPH FOR AT
LEAST ONE HOUR OR GUSTS OF 45-57 MPH/ BUT THIS WILL HAVE TO BE
WATCHED BY LATER SHIFTS. ANOTHER VORT LOBE ROTATES THROUGH THE
REGION ON WED NIGHT INTO THU. EXPECTING ONLY AN INCREASE IN CLOUDS
GIVEN LIMITED MOISTURE AND ISENTROPIC DESCENT NOTED ON THE 290-300K
SFCS. MODELS STILL SHOW A SECONDARY SURGE OF COLDER AIR SWD INTO
MO/IL WITH THIS VORT LOBE...THEREFORE MAINTAINED GOING COOL
TEMPERATURES FOR THU/FRI. FRI NIGHT LOOKS ESPECIALLY CHILLY GIVEN
THE SFC HIGH BUILDING IN OVERHEAD AND THE POTENTIAL FOR GOOD
RADIATIONAL COOLING CONDITIONS IF SKIES REMAIN CLEAR. SFC HIGH
SHIFTS EWD ON SAT BUT GFS/ECMWF BEGIN TO DIVERGE. GIVEN MODEL
DISAGREEMENT...REFRAINED FROM ADDING SCHC POPS TO THE EXTENDED FCST
AND STAYED CLOSE TO HPC TEMPERATURE GUIDANCE FOR SAT AND BEYOND.

KANOFSKY

&&

.AVIATION...
/718 PM CDT SUN OCT 24 2010/

TSTMS HAVE DVLPD AS SCHEDULED THO A LITTLE FURTHER NW THAN XPCTD.
ONE LINE EXTNDS FROM TROY MO NE TO OTTAWA IL. A SECOND LINE HAS
DVLPD FROM ROLLA MO NE TO LITCHFIELD IL. THIS ACTIVITY IS MOVG NE.
FIRST LINE SHOULD NOT IMPACT ANY OF THE TAF SITES...BUT THE
SECOND LINE HAS DVLPD RIGHT OVER THE STL METRO AREA. INTRODUCED A
TEMPO GROUP FOR THIS CONVECTION AT KSTL/KSUS. MVFR VSBYS WILL BE
POSSIBLE IN ASSOC WITH THE STRONGER STORMS ALONG WITH HALF TO
THREE QUARTER INCH HAIL. TSTMS SHOULD BE OUT OF THE AREA BY 6Z
WITH CLEARING TAKING PLACE OVERNIGHT. WINDS SHOULD PICK UP AGAIN
MONDAY AFTERNOON IN ADVANCE OF THE NEXT WEATHER SYSTEM DUE INTO
THE TAF SITES MONDAY NIGHT. CLOUDS WILL THICKEN AND LOWER MONDAY
AFTERNOON AND EVENING WITH THE BULK OF THE SIG WX AFTER THIS
PERIOD.

SPECIFICS FOR KSTL...

BROKEN LINE OF SHRA WITH ISLD TSTMS HAS DVLPD RIGHT OVER THE
TERMINAL. EXPECT THIS ACTIVITY TO CONTINUE MOVING NE AND IMPACT THE
SITE THRU 2-3Z. THE STRONGER STORMS WILL BE CAPABLE OF MVFR VSBYS
ALONG WITH HALF TO THREE QUARTER INCH HAIL. THIS CONVECTION WILL
END PRIOR TO MIDNIGHT AND CLEARING SHOULD TAKE PLACE OVERNIGHT.
CLOUDS WILL THICKEN AND LOWER MONDAY IN ADVANCE OF A COLD FRONT
EXPECTED TO ARRIVE AFTER 6Z MONDAY NIGHT. WINDS WILL ALSO INCREASE
DURING THE AFTERNOON AND EVENING IN RESPONSE TO THE TIGHTENING
PRESSURE GRADIENT AHEAD OF THE COLD FRONT.

MILLER

&&

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

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
317 PM CDT SUN OCT 24 2010

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-251245-
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-
317 PM CDT SUN OCT 24 2010

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 ACROSS THE AREA TONIGHT. A FEW
OF THE STORMS COULD PRODUCE DAMAGING WINDS GUSTS AND LARGE HAIL.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

A LINE OF THUNDERSTORMS IS EXPECTED TO DEVELOP ALONG A COLD FRONT
AND MOVE QUICKLY ACROSS THE REGION ON MONDAY NIGHT INTO TUESDAY. A
FEW OF THE STORMS WITHIN THE LINE MAY BE SEVERE...ESPECIALLY
ACROSS NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS.

SOUTHWEST WINDS ARE EXPECTED TO GUST UP TO 35 MPH ON TUESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE TONIGHT.

KANOFSKY

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