Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 281739
AFDLSX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ST LOUIS MO
1239 PM CDT FRI AUG 28 2015

.UPDATE:
ISSUED AT 1237 PM CDT FRI AUG 28 2015

THE AREA HAS REMAINED DRY EVEN THROUGH CLOUDS HAVE OVERSPREAD MOST
OF THE REGION. THERE MAY STILL BE SOME ISOLATED THUNDERSTORMS
DEVELOP LATER THIS AFTERNOON AS WEAK SHORTWAVE TROUGH NOW OVER
WESTERN MISSOURI MOVES EASTWARD. UNTIL THEN...STILL EXPECT HIGHS
TO RANGE FROM THE UPPER 70S TO MID 80S UNDER PARTLY SUNNY SKIES.

BRITT

&&

.SHORT TERM:  (THROUGH LATE THIS AFTERNOON)
ISSUED AT 340 AM CDT FRI AUG 28 2015

MID AND HIGH CLOUDS ASSOCIATED WITH SHOWERS AND THUNDERSTORMS
CONTINUE TO STREAM IN ACROSS FORECAST AREA EARLY THIS MORNING AHEAD
OF COLD FRONT. DESPITE LOW LEVEL MOISTURE THAT WILL BE ON THE
INCREASE TODAY ON SOUTHERLY FLOW AHEAD OF THE COLD FRONT, THERE IS A
LOT OF DRY AIR TO OVERCOME. FEEL THAT BEST CHANCES OF SOME SHOWERS
AND A FEW THUNDERSTORMS WILL BE OVER CENTRAL AND NORTHEAST MISSOURI
AS WELL AS WEST CENTRAL ILLINOIS, BUT COVERAGE WILL BE SCATTERED.
OTHERWISE, TEMPERATURES TO REMAIN A BIT BELOW NORMAL IN THE LOW TO
MID 80S.

BYRD

.LONG TERM:  (TONIGHT THROUGH THURSDAY)
ISSUED AT 340 AM CDT FRI AUG 28 2015

THERE IS GOOD AGREEMENT IN THE 00Z GUIDANCE THAT FRONTAL
BOUNDARY AND ASSOCIATED SHORTWAVE SHOULD ALLOW THUNDERSTORMS
THREAT TO SLOWLY EXPAND OVER THE NORTHWEST HALF OF THE CWA
TONIGHT...WITH THE STL METRO LIKELY ON THE EASTERN EDGE OF THE
THREAT DURING THE PREDAWN HOURS.  DUE TO PROGGED LOW LEVEL
FORCING AHEAD OF THE FRONT, HAVE UPPED POPS INTO LIKELY CATEGORY
OVER OUR EXTREME NORTHWEST COUNTIES.

HOWEVER...FROM SATURDAY MORNING ON FEATURES AND MODEL SPECIFICS
BEGIN TO DIVERGE AND BECOME INCREASING NEBULOUS.  WHILE MODELS DO
AGREE THAT NORTHERN PORTION OF THE SHORTWAVE WILL CONTINUE TO PRESS
INTO THE LOWER GREAT LAKES DURING THE DAY...THEY DISAGREE WITH THEIR
HANDLING OF THE SOUTHERN PORTION OF THE SHORTWAVE ENERGY AS IT
STRETCHES SOUTHEAST AND POSSIBLY MERGING WITH ANOTHER WEAK
CIRCULATION ALONG THE GULF COAST (WHICH APPEARS TO ORIGINATE WITH
A BIT OF ENERGY THAT BREAKS OFF FROM THE BASE OF THE CURRENT EAST
COAST TROF). GFS AND NAM SUGGEST SOME TYPE OF REMNANT CIRCULATION
TAKING UP RESIDENCE IN THE VICINITY OF SW MO BY SUNDAY WITH
RESIDUAL SURFACE FRONT BECOMING STATIONARY OVER THE AREA...WHILE
ECMWF WANTS TO PUSH THE INCREASINGLY WEAK SHORTWAVE ENERGY AND
SURFACE BOUNDARY SOUTH WITH TIME.

IF NAM AND GFS SOLUTIONS DO COME TO FRUITION ON SUNDAY...AND IF NAM
LOW LEVEL MOISTURE FORECAST (WHICH IS OFTEN TOO HIGH) ALSO
VERIFIES...THEN THE DRY FORECAST ON SUNDAY WILL BE IN JEOPARDY.
HOWEVER...WOULD LIKE TO SEE ADDITIONAL SUPPORT FOR THESE WEAK
FEATURES AND TRENDS BEFORE REINTRODUCING CONVECTION ON SUNDAY.  SO
FOR NOW HAVE CONTINUED TO TREND THE FORECAST TO THE ECMWF
SOLUTION...NAMELY THUNDERSTORM CHANCES EXPANDING SOUTHEAST ACROSS
THE CWA DURING THE DAY ON SATURDAY THEN GRADUALLY DIMINISHING FROM
NW TO SE LATE SATURDAY AFTERNOON AND SATURDAY NIGHT.

DESPITE THE DISCREPANCY IN THE UA PROGS ON SUNDAY...MEDIUM RANGE
SOLUTIONS REMAIN IN GOOD RUN TO RUN AND MODEL TO MODEL AGREEMENT
THAT WESTERN RIDGE WILL BE EXPANDING EAST INTO THE MID
MISSISSIPPI AND OHIO VALLEYS DURING THE UPCOMING WEEK. THIS SHOULD
MEAN DRY WEATHER FOR THE FA...ALONG WITH TEMPERATURES REBOUNDING
TO LATE SUMMER LEVELS WITH HIGHS IN THE UPPER 80S-LOWER 90S.

TRUETT

&&

.AVIATION:  (FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1237 PM CDT FRI AUG 28 2015

EXPECT MAINLY DRY AND VFR CONDITIONS THROUGH THIS EVENING. THEN
EXPECT SCATTERED SHOWERS AND THUNDERSTORMS TO DEVELOP ACROSS
CENTRAL AND NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS OVERNIGHT
THAT WILL EVENTUALLY SPREAD INTO THE ST. LOUIS METRO AREA ON
SATURDAY MORNING. SCATTERED THUNDERSTORMS WILL CONTINUE TO DEVELOP
ON SATURDAY AFTERNOON AROUND THE ST. LOUIS METRO TAF SITES.

SPECIFICS FOR KSTL: EXPECT MAINLY DRY AND VFR CONDITIONS THROUGH
TONIGHT. THEN SCATTERED SHOWERS WILL MOVE INTO THE AREA BY LATE
SATURDAY MORNING WITH AN INCREASING CHANCE OF SCATTERED
THUNDERSTORMS AS AN UPPER LEVEL STORM SYSTEM MOVES INTO THE AREA
BY LATE SATURDAY AFTERNOON.

BRITT

&&

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

$$

WFO LSX


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