712
FXUS63 KLSX 081858
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
158 PM CDT MON SEP 8 2025
KEY MESSAGES
- WELL-ABOVE NORMAL TEMPERATURES AND DRY WEATHER IS FORECAST
STARTING THURSDAY AND LASTING AT LEAST THROUGH THIS WEEKEND.
SHORT TERM
(THROUGH LATE TUESDAY AFTERNOON)
ISSUED AT 156 PM CDT MON SEP 8 2025
THE STUBBORN SURFACE RIDGE OF HIGH PRESSURE WILL REMAIN IN PLACE
TONIGHT ACROSS THE BI-STATE REGION, THOUGH SOME WEAK RETURN FLOW
WILL BE IN PLACE ACROSS PARTS OF CENTRAL/NORTHEAST MISSOURI. A
MOSTLY CLEAR SKY, LIGHT/VARIABLE WINDS, AND LOW DEWPOINTS WILL
FOSTER VERY GOOD CONDITIONS FOR RADIATIONAL COOLING AGAIN TONIGHT.
THIS MEANS ANOTHER CHILLY NIGHT FOR EARLY SEPTEMBER, WITH LOWS IN
THE MID 40S TO LOW 50S. THESE READINGS WOULD BE ABOUT 10 DEGREES
BELOW NORMAL FOR THE DATE.
THE WARMUP WILL REALLY BEGIN ON TUESDAY AS LOW-LEVEL WARM AIR
ADVECTION INCREASES AS THE SURFACE RIDGE FINALLY BREAKS DOWN. AN
INCREASE IN MID/HIGH LEVEL CLOUDINESS MAY MITIGATE THE WARMUP
SLIGHTLY, BUT HIGHS ARE STILL EXPECTED TO CLIMB INTO THE UPPER 70S
TO LOW 80S.
GOSSELIN
LONG TERM
(TUESDAY NIGHT THROUGH NEXT MONDAY)
ISSUED AT 156 PM CDT MON SEP 8 2025
(TUESDAY NIGHT - THURSDAY NIGHT)
TEMPERATURES WILL CONTINUE TO MODERATE HEADING INTO MIDWEEK AS
MID/UPPER LEVEL HEIGHTS RISE AND 850-HPA TEMPERATURES WARM INTO THE
+16 TO +20C RANGE. ABOVE-NORMAL TEMPERATURES (HIGHS IN 80S AND LOWS
IN MID 50S/LOW 60S) ARE EXPECTED ALONG WITH DRY WEATHER. A FEW STRAY
SHOWERS CANNOT BE COMPLETELY RULED OUT LATE TUESDAY NIGHT AND EARLY
WEDNESDAY MORNING IN PARTS OF NORTHEAST MISSOURI. THIS IS WHERE
THERE IS SOME BROAD, MODEST LOW-LEVEL MOISTURE ADVECTION. THE
MIDLEVEL ASCENT AHEAD OF A SHORTWAVE TROUGH HOWEVER IS DISPLACED
NORTHEAST MORE TOWARD THE GREAT LAKES. IN ADDITION, THE LOWEST
LEVELS OF THE ATMOSPHERE REMAIN QUITE DRY. GIVEN THIS AND THE FAIRLY
WEAK FORCING FOR ASCENT DETAILED ABOVE, VIRGA MAY BE THE MOST LIKELY
OUTCOME.
(FRIDAY - NEXT MONDAY)
ENSEMBLE GUIDANCE IS IN VERY GOOD AGREEMENT THAT THE MID/UPPER LEVEL
RIDGE WILL BUILD INTO THE MID-MISSISSIPPI VALLEY HEADING INTO THIS
WEEKEND. THIS PORTENDS TO EVEN HOTTER TEMPERATURES. HIGHS IN THE LOW
TO MID 90S ARE FORECAST FRIDAY THROUGH SUNDAY, OR ABOUT 10-15
DEGREES ABOVE NORMAL. THE AIRMASS IS QUITE STRONG, WITH 850-HPA
TEMPERATURES ON THE NAEFS AROUND +20C (>95TH PERCENTILE OF
CLIMATOLOGY). THESE HIGHS WON'T THREATEN DAILY RECORDS, WHICH NEAR
OR SLIGHTLY ABOVE THE CENTURY MARK, BUT THEY WILL BE A BIT OF A JOLT
FROM THE MID/LATE FALL LIKE READINGS WE HAVE EXPERIENCED OVER THE
PAST SEVERAL DAYS.
ENSEMBLE SPREAD BEGINS TO INCREASE AS WE HEAD INTO EARLY NEXT WEEK.
THE FOUR CLUSTERS OF THE 500-HPA HEIGHT PATTERN FROM THE GRAND
ENSEMBLE ALL AGREE THAT AT LEAST SOME WEAKENING OF THE MID/UPPER
LEVEL RIDGE ACROSS THE MISSISSIPPI VALLEY WILL TAKE PLACE, BUT HOW
MUCH IS AN OPEN QUESTION. THE OVERALL PATTERN LOOKS A BIT LESS
AMPLIFIED AND MORE "BLOCKY", WITH A QUASI-OMEGA BLOCK SETTING UP
ACROSS THE CONUS. THERE IS MORE SPREAD WITH RESPECT TO THE STRENGTH
OF MID/UPPER LEVEL TROUGHING TRYING TO DIG INTO THE GREAT
LAKES/NORTHEAST. TWO OF THE FOUR CLUSTERS (~53% OF MEMBERS) SHOW A
FAIRLY STRONG TROUGH THAT IS MUCH WEAKER OR ABSENT ENTIRELY IN THE
OTHER TWO CLUSTERS. THE SCENARIO WITH A STRONGER TROUGH IN THE GREAT
LAKES/NORTHEAST WOULD LIKELY BRING DOWN A BACKDOOR COLD FRONT
THROUGH THE REGION EARLY/MID NEXT WEEK AND LEAD TO A MORE
SUBSTANTIAL COOL DOWN. HOWEVER, THE OTHER SCENARIO WITH WEAKER
TROUGHING WOULD LIKELY MEAN NO FRONTAL PASSAGE AND MORE OF A
CONTINUATION OF THE ANOMALOUS WARMTH. REGARDLESS, PRECIPITATION
CHANCES LOOK LOW WITH NO DISCERNIBLE SIGNAL WHATSOEVER FOR ANYTHING
SIGNIFICANT OR WIDESPREAD. PROBABILITIES FROM THE LREF OVER A 24-
HOUR PERIOD ENDING MONDAY EVENING DO INCREASE TO AROUND 40-50% FOR
MEASURABLE PRECIPITATION ASSOCIATED WITH THE POSSIBLE BACKDOOR COLD
FRONT, BUT DROP BELOW 10% FOR A QUARTER INCH OR MORE OF RAINFALL.
GOSSELIN
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1208 PM CDT MON SEP 8 2025
DRY/VFR CONDITIONS ARE EXPECTED THROUGH TUESDAY MORNING WITH LIGHT
SOUTHEAST WINDS. SOME INCREASE IN MID/HIGH LEVEL CLOUDINESS WILL
OCCUR FROM WEST TO EAST BEGINNING TONIGHT.
THERE IS A CONCERN FOR SOME STEAM FOG TONIGHT IN RIVER VALLEYS,
MAINLY IN EAST CENTRAL AND SOUTHEAST MISSOURI. A BRIEF PERIOD OF
LOWER VISIBILITIES IS EXPECTED AT KSUS, SO ADDED A TEMPO 3SM BR.
KJEF SHOULD HAVE ENOUGH OF A SOUTHERLY WIND AND SOME CLOUDS TO
PREVENT FOG FORMATION ALONG THE MISSOURI RIVER THAT FAR WEST.
GOSSELIN
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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