Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 291832
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
132 PM CDT WED JUL 29 2015

.UPDATE:
ISSUED AT 1159 AM CDT WED JUL 29 2015

EXCESSIVE HEAT WARNING WILL BE CANCELLED SHORTLY FOR A GOOD CHUNK
OF THE AREA. CLOUDS AND AND LOWER DEWPOINTS ARE FILTERING IN
BEHIND THE FRONT AND IT LOOKS LIKE 105 HEAT INDEX VALUES WON`T BE
ACHIEVED TODAY.

CARNEY

&&

.SHORT TERM:  (THROUGH LATE THIS AFTERNOON)
ISSUED AT 311 AM CDT WED JUL 29 2015

08Z SURFACE ANALYSIS REVEALS THAT THE EAGERLY-AWAITED COLD FRONT
(AND ITS NOTICEABLY LESS HUMID POST-FRONTAL AIR MASS) WAS
TANTALIZINGLY CLOSE TO THE LSX CWA EARLY THIS MORNING. AT 08Z,
THE FRONT STRETCHED FROM CENTRAL KS THROUGH EXTREME SOUTHEASTERN
NEB AND THROUGH CENTRAL IA INTO WESTERN WI. A NOCTURNAL MCS AHEAD
OF THE FRONT WAS MAKING STEADY SOUTHWARD PROGRESS BUT VERY SLOW
EASTWARD PROGRESS. ADDITIONAL THUNDERSTORMS ARE POSSIBLE WITH THE
FRONT TODAY AS IT MOVES INTO A MOIST AND UNSTABLE AIR MASS DURING
THE AFTERNOON HOURS, AND THE OUTFLOW BOUNDARY MAY ALSO SERVE AS A
TRIGGER FOR AFTN SH/TS.

UNTIL THE COLD FRONT ARRIVES, THERE WILL BE VERY LITTLE CHANGE IN
THE SOUPY AIR MASS STILL IN PLACE ACROSS THE REGION. THE TIMING
OF THE COLD FRONT IS SUCH THAT ROUGHLY THE SOUTHERN TO
SOUTHEASTERN HALF OF THE CWA SHOULD SEE ANOTHER DAY OF HOT/HUMID
CONDITIONS, ALBEIT NOT AS OPPRESSIVE AS YESTERDAY. HEAT INDEX
VALUES SHOULD BE CLOSER TO 105-109 IN THE WORST AREAS TODAY
COMPARED TO THE HEAT INDICES OF 110-117 WHICH WERE OBSERVED
YESTERDAY. DESPITE THE SLIGHTLY LOWER HEAT INDEX VALUES WHICH ARE
EXPECTED TODAY, THE EXCESSIVE HEAT WARNING STILL LOOKS APPROPRIATE
BECAUSE IT IS THE CUMULATIVE EXPOSURE TO EXCESSIVE HEAT WHICH
NEGATIVELY AFFECTS THE HUMAN BODY, AND TODAY WILL BE THE THIRD OR
FOURTH DAY OF SUCH CONDITIONS FOR SOME AREAS.

KANOFSKY

.LONG TERM:  (TONIGHT THROUGH TUESDAY)
ISSUED AT 311 AM CDT WED JUL 29 2015

A TWO-DAY RESPITE FROM THE OPPRESSIVE HEAT/HUMIDITY IS EXPECTED
ON THU/FRI. TEMPERATURES SHOULD BE SEASONABLY WARM (UPPER 80S TO
LOWER 90S), BUT THE DEW POINTS WILL BE MUCH LOWER THAN THEY HAVE
BEEN RECENTLY.

THE UPPER AIR PATTERN WILL HAVE TRANSITIONED TO NORTHWEST FLOW
ALOFT BY FRIDAY DUE TO THE BUILDING RIDGE ACROSS THE WESTERN CONUS
AND A TROUGH OVER THE EASTERN CONUS. MODELS SHOW THAT THIS NW
FLOW PATTERN REMAINS UNCHANGED THROUGH EARLY NEXT WEEK. ALTHOUGH
THE MODELS CONTINUE TO SHOW HINTS OF A SHORTWAVE OR TWO WHICH
COULD SUPPORT CONVECTION (PERHAPS AS EARLY AS SATURDAY NIGHT),
CONFIDENCE IN THE TIMING AND PLACEMENT OF THESE FEATURES IS LOW.
TEMPERATURES LOOK SEASONABLY WARM IN THE UPPER 80S TO LOWER 90S
THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.

KANOFSKY

&&

.AVIATION:  (FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1248 PM CDT WED JUL 29 2015

VFR FCST AT THE TERMINALS THRU THE PRD. SFC COLD FRONT IS SOUTH
OF ALL THE TERMINAL AS OF EARLY THIS AFTN...ACROSS STHRN IL INTO
SE MO. ISLD CONVECTION IS IN THE PROCESS OF DVLPNG ALONG THE BNDRY
ACROSS STHRN IL AS OF 18Z...AND EXPECT THIS TO CONTINUE TO DVLP TO
THE SW ACROSS SE MO. THIS ACTIVITY IS DVLPNG WITHIN THE BAND OF
MVFR CIGS THAT MOVED THRU THE STL METRO TERMINALS. THE SHRAS/TSTMS
WILL CONTINUE TO PUSH SE ALONG WITH THE BNDRY. BEHIND THE
FRONT...WINDS HAVE TURNED TO THE NORTH FILTERING IN DRIER AIR.
WINDS WILL GRADUALLY BECOME W/WNW BY THU MRNG.

SPECIFICS FOR KSTL:

VFR FCST THRU THE PRD WITH N WIND THIS AFTN BCMNG W/WNW BY THRU
MRNG. THE THREAT OF PRECIP IS FCST TO REMAIN SOUTH OF THE TERMINAL
THIS AFTN.

2%

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...EXCESSIVE HEAT WARNING UNTIL 9 PM CDT THIS EVENING FOR IRON MO-
     MADISON MO-REYNOLDS MO-ST. FRANCOIS MO-STE. GENEVIEVE MO.

IL...EXCESSIVE HEAT WARNING UNTIL 9 PM CDT THIS EVENING FOR MARION IL-
     RANDOLPH IL-WASHINGTON IL.

&&

$$

WFO LSX


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