Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 290418
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1118 PM CDT TUE JUL 28 2015

.UPDATE:
ISSUED AT 915 PM CDT TUE JUL 28 2015

BIGGEST CHANGE WAS TO EXTENDED THE EXCESSIVE HEAT WARNING THROUGH
WEDNESDAY IN THE ST. LOUIS METRO AND SURROUND AREAS TO THE SOUTH.
TEMPERATURES WON`T COOL OFF MUCH TONIGHT AND SHOULD WARM RAPIDLY
ON WEDNESDAY MORNING BEFORE THE FRONT PUSHES THROUGH THE AREA.
WHILE WE SHOULDN`T SEE THE EXTREME HEAT OF THE LAST FEW DAYS, THE
HEAT INDEX VALUES WILL RISE INTO THE 100-106 RANGE GIVEN THE
POOLING OF DEW POINTS IN THE MIDDLE AND UPPER 70S AND TEMPS RISING
QUICKLY INTO THE LOWER 90S, AND THIS WILL KEEP THE LONGEVITY OF
DANGEROUS HEAT LEVELS GOING.

OTHERISE THE FRONT WILL SAG SOUTH TONIGHT BRINGING SCATTERED
THUNDERSTORMS TO PORTIONS OF NORTHERN MISSOURI INTO WEST CENTRAL
IL.

GLASS

&&

.SHORT TERM:  (THROUGH LATE TONIGHT)
ISSUED AT 349 PM CDT TUE JUL 28 2015

DANGEROUS HEAT INDICES ARE CURRENTLY IN THE 105-117F RANGE OVER
THE AREA WITH TEMPERATURES WELL INTO THE 90S. LAMBERT IS CURRENTLY
REPORTING 100. THESE VALUES SHOULD FALL OFF BELOW CRITERIA BY 9
PM. ISOLATED THUNDERTORMS ARE BEGINNING TO DEVELOP OVER THE AREA
AS ATMOSPHERE IS CURRENTLY UNCAPPED AND MLCAPES ARE BETWEEN
3000-4000 J/KG. ANY STORMS THAT DO DEVELOP THIS AFTERNOON MAY
BECOME STRONG AND MAY PRODUCE GUSTY WINDS AND HEAVY DOWNPOURS
BEFORE THE STORMS DIMINISH AROUND SUNSET. THERE WILL BE A BETTER
CHANCE OF STORMS LATER TONIGHT AS A COLD FRONT MOVES INTO THE
NORTHERN PART OF THE CWA. HAVE KEPT WITH BEST CHANCES OF
THUNDERSTORMS NORTH OF I-70 WHERE THERE WILL BE THE BEST
COMBINATION OF ASCENT FROM PASSING TROUGH TO THE NORTH WITH LOW
LEVEL MOISTURE CONVERGENCE.

.LONG TERM:  (WEDNESDAY THROUGH NEXT TUESDAY)
ISSUED AT 349 PM CDT TUE JUL 28 2015

(WEDNESDAY THROUGH FRIDAY)

HAVE EXTENDED THE HEAT WARNING FOR THE FAR SOUTHERN PART OF THE CWA
INTO THE TOMORROW AFTERNOON.  EVEN THOUGH THE COLD FRONT WILL MOVE
THROUGH THE AREA EARLY IN THE DAY...THERE WON`T BE A STRONG PUSH OF
COOLER AND DRIER AIR INTO SOUTHEAST MISSOURI AND SOUTHERN ILLINOIS
UNTIL WEDNESDAY NIGHT.  BECAUSE OF THIS, DEWPOINTS WILL STILL BE IN
THE MID 70S WITH HIGH TEMPERATURES CLIMBING INTO THE LOW 90S WHICH
WILL ALLOW HEAT INDEX READINGS TO CLIMB TO AROUND 105 DEGREES DURING
THE AFTERNOON.  COOLER AND DRIER WEATHER WILL MOVE INTO THE AREA FOR
THURSDAY AND FRIDAY.

SCATTERED THUNDERSTORMS WILL MOVE ACROSS WITH THE FRONT ON WEDNESDAY
MORNING.  THESE STORMS WILL BE MAINLY CONFINED ALONG AND SOUTH OF I-
44 IN MISSOURI AND ALONG AND SOUTH OF I-70 IN ILLINOIS DURING THE
AFTERNOON.  THURSDAY AND FRIDAY LOOK DRY AT THIS POINT.

(SATURDAY THROUGH TUESDAY)

ECMWF AND GFS CONTINUE TO ADVERTISE NORTHWESTERLY UPPER FLOW FOR EARLY
NEXT WEEK WITH A LARGE HIGH OVER THE SOUTHWESTERN CONUS AND LARGE
MEAN TROUGH OVER EASTERN NORTH AMERICA.  THE OPERATIONAL GFS BEGINS
TO FLATTEN THE FLOW OVER THE RIDGE BY TUESDAY WHEREAS THE ECMWF
KEEPS THE FLOW OVER MIDWEST MORE NORTHWESTERLY.  THE ECMWF HAS BEEN
MORE CONSISTENT AND HAS SUPPORT FROM THE GFS ENSEMBLE MEAN, SO WILL
KEEP WITH IT`S SOLUTION.  WILL KEEP WITH A DRY FORECAST OVER THE
WEEKEND INTO MONDAY AS HIGH PRESSURE MOVES ACROSS THE AREA.  BY LATE
ON TUESDAY A FRONT WILL BEGIN TO APPROACH THE AREA FROM THE NORTH
WHICH WILL INCREASE THUNDERSTORMS CHANCES AS THE ATMOSPHERE BECOMES
MORE UNSTABLE LATE IN THE DAY.  TEMPERATURES WILL BE CLOSE TO LATE
JULY NORMALS WITH 850MB TEMPERATURES BETWEEN 18-22C.

BRITT

&&

.AVIATION:  (FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1101 PM CDT TUE JUL 28 2015

THUNDERSTORMS OVER THE MO/IA BORDER HAVE BEEN WEAKENING A BIT
THUS SPC DOES NOT ANTICIPATE A WATCH FOR NE MO AND WC IL. VERY
UNSTABLE AIR BUT SYNOPTIC FORCING IS WEAK AND DAYTIME HEATING IS
GONE. STILL EXPECT SOME STORMS TO MAKE IT TO UIN MOST LIKELY FROM
7Z - 10Z. MODELS DECREASNG THE COVERAGE OVERNIGHT BUT STILL THINK
A MENTION AS THE FRONT APPROACHES IS WARRANTED. ANOTHER QUESTION
IS WILL STORMS FORM WEDNESDAY AFTERNOON. NAM HAS BEEN CONSISTENT
IS DEVELOPING SOME AND IT HAS BEEN OK LATELY SO WILL GO WITH IT
SOME VCTS FOR THE AFTERNOON.

SPECIFICS FOR KSTL: FRONT WILL APPROACH STL 12Z-15Z WITH A WEST
WIND INITTIALLY THEN NORTHWEST BY 15Z. MODELS WEAKEN AND DIMINISH
COVERAGE OF THE CONVECTION OVER THE MO/IA BORDER AS IT MOVES EAST
SOUTHEAST OVERNIGHT...HOWEVER MOST KEEP SOME PRECIPITATON ALONG
THE FRONT SO WILL INTRODUCE A VCTY FOR THE EARLY MORNING. NAM HAS
CONSISTENTLY BEEN RE-DEVELOPING FOR WEDNESDAY AFTERNOON SO WILL
ALSO CARRY A VCTS FOR THIS TIME AS WELL.

JPK

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...EXCESSIVE HEAT WARNING UNTIL 9 PM CDT WEDNESDAY FOR CRAWFORD MO-
     FRANKLIN MO-IRON MO-JEFFERSON MO-MADISON MO-REYNOLDS MO-ST.
     CHARLES MO-ST. FRANCOIS MO-ST. LOUIS CITY MO-ST. LOUIS MO-
     STE. GENEVIEVE MO-WASHINGTON MO.

IL...EXCESSIVE HEAT WARNING UNTIL 9 PM CDT WEDNESDAY FOR CLINTON IL-
     MADISON IL-MARION IL-MONROE IL-RANDOLPH IL-ST. CLAIR IL-
     WASHINGTON IL.

&&

$$

WFO LSX


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