Severe Thunderstorm Warning 226, NWS St. Louis, MO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
242 PM CDT FRI AUG 13 2010

.DISCUSSION...
/134 PM CDT FRI AUG 13 2010/

TONIGHT THROUGH SUNDAY...THE FIRST OF TWO SHORTWAVE TROFS TO
AFFECT THE REGION WAS LOCATED ACROSS NE/KS AT 19Z. THE SECOND
SHORTWAVE TROF WAS LOCATED FARTHER UPSTREAM OVER MT/ID. THESE
SHORTWAVES WILL PROVIDE UPPER LEVEL FORCING TO SUPPORT
THUNDERSTORMS THIS AFTERNOON/TONIGHT AND AGAIN ON
SATURDAY/SATURDAY NIGHT AS A COLD FRONT MOVES INTO THE AREA.
GIVEN AMPLE INSTABILITY AND LIMITED WIND SHEAR...A FEW STORMS MAY
BE SEVERE AND CAPABLE OF PRODUCING DAMAGING WIND GUSTS AND LARGE HAIL.
ONGOING STORMS IN NWRN MO ARE EXPECTED TO DEVELOP INTO A QLCS AND
PROGRESS ACROSS PARTS OF NORTHERN MISSOURI AND WEST CENTRAL
ILLINOIS EARLY THIS EVENING. PW VALUES AROUND 2 INCHES /99TH
PERCENTILE FOR SWRN MO IN AUG/ AND DEEP WARM CLOUD LAYERS SUGGEST
HEAVY RAINFALL MAY ALSO BECOME A CONCERN.

CDFNT WILL BE MOVING THROUGH THE CWA ON SATURDAY AS LARGE SCALE
LIFT INCREASES AHEAD OF THE SECOND SHORTWAVE TROF. HOT AND HUMID
AIR MASS AHEAD OF THE FRONT ON SATURDAY WILL SUPPORT THUNDERSTORMS
ACROSS THE AREA. A FEW OF THE STORMS ON SATURDAY COULD BE SEVERE
AND CAPABLE OF PRODUCING DAMAGING WIND GUSTS.

H85 FNT LAGS THE SFC FNT AND WILL BE ACROSS THE CWA ON SUN AFTN.
H85 MCONV MAY SUPPORT ISO/SCT TSRA ON SUN AFTN AND THUS MAINTAINED
GOING SCHC POPS ACROSS THE SRN HALF OF THE CWA. COOLER AND LESS
HUMID AIR FILTERS IN TO THE REGION BEHIND THE CDFNT...PROVIDING A
MUCH NEEDED BREAK FROM THE ONGOING OPPRESSIVE HEAT.

MON THROUGH FRI...PATTERN TRANSITION LEAVES THE CWA IN WEAK NW FLOW
ALOFT BY MON/TUE AS A LONGWAVE TROF SETTLES OVER SERN CANADA AND THE
NERN US WHILE A SFC HIGH SLIDES SEWD OUT OF THE NRN PLAINS. MUCH NEEDED
BREAK FROM THE HEAT SHOULD LAST FOR AT LEAST A FEW DAYS AS H85
TEMPERATURES FALL TO 14 TO 16 DEG C BY TUE AND DRIER AIR FILTERS
INTO THE REGION. SHORTWAVES MOVING THROUGH THE FLOW WILL PROBABLY
SUPPORT TSRA ON SOME DAYS NEXT WEEK BUT I HAVE LOW CONFIDENCE IN
THE TIMING OF THESE IMPULSES...ESPECIALLY SINCE THE MODELS STILL
DISAGREE ON SOME OF THE LARGE SCALE DETAILS. ECMWF/GFS/GEM
CONTINUE TO INDICATE PCPN CHCS FOR TUE THROUGH WED BUT THE
METEOROLOGICAL REASON SEEMS TO CHANGE WITH EACH RUN. YESTERDAY THE
ECMWF DEPICTED A SHORTWAVE TROF DROPPING SEWD OUT OF CANADA BUT
TODAY IT DEPICTS A SHORTWAVE MUCH FARTHER SOUTH.
SIMILARLY...YESTERDAY'S GFS DEPICTION OF A GULF COAST LOW MOVING
NWD INTO MO/IL HAS BEEN REPLACED WITH HINTS OF A WEAK SHORTWAVE IN
NEARLY ZONAL FLOW FOLLOWED BY A STRONGER VORT MAX MOVING THROUGH
SRN CANADA. GFS/ECMWF IN BROAD AGREEMENT THAT RIDGING ALOFT
RETURNS TO THE AREA FOR THU BUT THERE IS DISAGREEMENT ON THE
DURATION. FOR THESE REASONS...I HAVE LOW CONFIDENCE IN THE LAST
FEW PERIODS OF THE EXTENDED FORECAST.

KANOFSKY

&&

.AVIATION...
/1125 AM CDT FRI AUG 13 2010/

HOT AND HUMID CONDTIONS CONTINUE WITH LIGHT SOUTH WIND. CHANCES OF
THUNDERSTORMS TO INCREASE LATE THIS AFTERNOON AND INTO THE EVENING
FROM NORTHWEST TO SOUTHEAST. LATEST SHORT RANGE MODEL GUIDANCE
WOULD SUGGEST LINE OF THUNDERSTORMS FORMING ACROSS SOUTHWEST IOWA
AND NORTHWEST MISSOURI WOULD REACH KUIN AROUND 23Z...KCOU AROUND
00Z...AND THE METRO TAF SITES AROUND 02Z. HAVE HIGHEST CONFIDENCE
AT KUIN...AND HAVE INCLUDED A TEMPO GROUP THERE. CONFIDENCE
DECREASES FURTHER SOUTH AND WILL NOWCAST THIS AFTERNOON WITH
LATEST RADAR TRENDS. ALOT OF UNCERTAINTY HEADING INTO THE
OVERNIGHT HOURS AS LOW LEVEL JET MAY CONTINUE TO FEED CONVECTION
ACROSS THE CWA.

SPECIFICS FOR KSTL...
VFR CONDITIONS TO CONTINUE THIS AFTERNOON. COULD SEE SOME ISOLATED
STORMS DEVELOP LATER THIS AFTERNOON...BUT BELIEVE THEY WILL BE
EVEN MORE ISOLATED THAN YESTERDAY. ATTENTION THEN TURNS TO THE
NORTHWEST AS ORGANIZED LINE OF CONVECTION COULD REACH KSTL THIS
EVENING. CONFIDENCE IN THIS SCENARIO IS NOT HIGH ENOUGH TO INCLUDE
A TEMPO...BUT RADAR TRENDS WILL NEED TO BE WATCHED.

CVKING

&&

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

     EXCESSIVE HEAT WARNING UNTIL 9 PM CDT THIS EVENING FOR KNOX MO-
     LEWIS MO-MARION MO-MONROE MO-RALLS MO-SHELBY MO.

IL...EXCESSIVE HEAT WARNING UNTIL 9 PM CDT SATURDAY FOR BOND 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.

     EXCESSIVE HEAT WARNING UNTIL 9 PM CDT THIS EVENING FOR ADAMS IL-
     BROWN IL.

&&

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
304 PM CDT FRI AUG 13 2010

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-141130-
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-
304 PM CDT FRI AUG 13 2010

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

.DAY ONE...TONIGHT

PEAK HEAT INDEX READINGS WILL RANGE FROM 105 TO 115 DEGREES
DURING EARLY EVENING HOURS...WITH THE WARMEST VALUES IN THE ST.
LOUIS METROPOLITAN AREA. PLEASE REFER TO THE EXCESSIVE HEAT
WARNING FOR MORE INFORMATION.

A FEW SEVERE THUNDERSTORMS WILL BE POSSIBLE TONIGHT. THE STRONGEST
STORMS WILL BE CAPABLE OF PRODUCING DAMAGING WIND GUSTS IN EXCESS
OF 60 MPH AND LARGE HAIL. THESE STORMS WILL ALSO BE CAPABLE OF
PRODUCING VERY HEAVY DOWNPOURS WHICH COULD CAUSE LOCALIZED
FLOODING IN LOW LYING AREAS.

MODERATE RIVER FLOODING CONTINUES ALONG THE MISSISSIPPI AT QUINCY
AND HANNIBAL. PLEASE SEE THE APPROPRIATE FLOOD STATEMENT FOR
SPECIFIC DETAILS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

DANGEROUS HEAT AND HUMIDITY WILL CONTINUE ON SATURDAY WITH PEAK
HEAT INDEX VALUES IN THE 105 TO 115 DEGREE RANGE DURING THE
AFTERNOON AND EARLY EVENING. THE EXCESSIVE HEAT WARNING WILL
REMAIN IN EFFECT UNTIL 9 PM IN AREAS ALONG AND SOUTH OF A COLUMBIA
MISSOURI TO PITTSFIELD ILLINOIS LINE.

THUNDERSTORMS ARE EXPECTED ACROSS THE AREA ON SATURDAY AND
SATURDAY NIGHT. A FEW OF THE STORMS COULD BE SEVERE AND CAPABLE OF
PRODUCING DAMAGING WIND GUSTS AND LOCALLY HEAVY DOWNPOURS.

MODERATE RIVER FLOODING IS FORECAST TO CONTINUE ALONG THE
MISSISSIPPI AT QUINCY AND HANNIBAL.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ASKED TO REPORT SEVERE WEATHER TO THE NATIONAL
WEATHER SERVICE OR LOCAL LAW ENFORCEMENT.

&&

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

KANOFSKY

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ST LOUIS MO
449 PM CDT FRI AUG 13 2010

ILZ095-096-MOZ019-027-132245-
ADAMS IL-BROWN IL-LEWIS MO-MARION MO-
449 PM CDT FRI AUG 13 2010

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN LEWIS...NORTHERN
MARION...ADAMS AND BROWN COUNTIES UNTIL 545 PM CDT...

AT 445 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING
STRONG THUNDERSTORMS ALONG A LINE EXTENDING FROM 6 MILES NORTH OF
WEST POINT TO MAYWOOD...AND MOVING EAST AT 35 MPH.

HAIL UP TO ONE-HALF INCH IN DIAMETER AND WIND GUSTS UP TO 40 MPH ARE
EXPECTED WITH THESE STORMS...ALONG WITH HEAVY RAIN AND FREQUENT
DANGEROUS LIGHTNING.

LOCATIONS NEAR THE PATH OF THESE STORMS INCLUDE...
  QUINCY...
  MENDON...
  GOLDEN...
  CAMP POINT...
  CLAYTON...
  BUCKHORN...
  MOUNT STERLING...
  TAYLOR...
  URSA...
  LORAINE...
  WOODVILLE...
  FOWLER...
  PALOMA...
  CHATTON...
  COATSBURG...
  LA PRAIRIE...
  BURTON...
  COLUMBUS...
  LIBERTY...
  MOUND STATION...

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.

GKS

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