Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 290912
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
412 AM CDT WED JUL 29 2015

.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 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 THIS EVENING 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 THIS EVENING FOR CLINTON
     IL-MADISON IL-MARION IL-MONROE IL-RANDOLPH IL-ST. CLAIR IL-
     WASHINGTON IL.

&&

$$

WFO LSX


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