581
FXUS63 KLSX 110240
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
940 PM CDT WED SEP 10 2025
KEY MESSAGES
- UNSEASONABLY HOT TEMPERATURES WILL CONTINUE INTO THE MIDDLE OF
NEXT WEEK.
- MOSTLY DRY WEATHER IS ALSO EXPECTED OVER THE NEXT 7 DAYS, THOUGH AT
LEAST A FEW SHOWERS/WEAK THUNDERSTORMS ARE POSSIBLE ON SUNDAY
AND MONDAY AFTERNOONS.
SHORT TERM
(THROUGH LATE THURSDAY AFTERNOON)
ISSUED AT 218 PM CDT WED SEP 10 2025
A MIDLEVEL SHORTWAVE TROUGH IS CURRENTLY MOVING ACROSS SOUTHEAST
KANSAS AND WILL MOVE INTO THE MID SOUTH BY EARLY THURSDAY MORNING.
THIS SYSTEM WILL STAY FAR ENOUGH SOUTHWEST TO LEAVE THE AREA HIGH
AND DRY, BUT SOME SCATTERED MID/HIGH LEVEL CLOUDINESS MAY IMPACT
PARTS OF SOUTHEAST MISSOURI. OTHERWISE, LOOK FOR A MOSTLY CLEAR
SKY WITH LIGHT WINDS OVERNIGHT. LOWS ARE EXPECTED TO DROP BACK
INTO THE UPPER 50S TO LOW 60S, OR RIGHT AROUND NORMAL FOR THE
DATE.
HIGHS ON THURSDAY SHOULD BE A COUPLE OF DEGREES WARMER THAN THIS
AFTERNOON, MAINLY DUE TO A SLIGHTLY WARMER START TO THE DAY AS WELL
AS 850-HPA TEMPERATURES WARMING ABOUT 0.5-1.0C. THERE SHOULD ALSO BE
PLENTY OF SUNSHINE AGAIN, THOUGH WE SHOULD SEE A BIT MORE DIURNAL
CUMULUS ESPECIALLY IN PARTS OF SOUTHEAST MISSOURI. HUMIDITY LEVELS
WILL ALSO CONTINUE TO INCREASE AS SURFACE DEWPOINTS CLIMB INTO THE
UPPER 50S TO LOW 60S.
GOSSELIN
LONG TERM
(THURSDAY NIGHT THROUGH NEXT WEDNESDAY)
ISSUED AT 218 PM CDT WED SEP 10 2025
THERE IS INCREASING CONFIDENCE THAT THE UNSEASONABLY HOT PATTERN
WILL CONTINUE THROUGH THIS WEEKEND AND INTO NEXT WEEK. ALL FOUR
CLUSTERS OF THE 500-HPA PATTERN FROM THE LREF AGREE THAT ANOMALOUS
MID/UPPER LEVEL RIDGING WILL REMAIN ENTRENCHED ACROSS THE
MISSISSIPPI VALLEY THROUGH EARLY NEXT WEEK. THERE IS A CLUSTER (~22%
OF MEMBERS) THAT STILL HAS DEEPER TROUGHING ACROSS THE GREAT LAKES
BY TUESDAY, BUT THIS IS COMPRISED OF MOSTLY GEPS MEMBERS. THIS
SCENARIO COULD STILL BRING US A BACKDOOR COLD FRONT AT LEAST INTO
PARTS OF OUR ILLINOIS COUNTIES, BUT THIS SCENARIO IS UNLIKELY AT
THIS JUNCTURE IN TIME. THE MOST LIKELY SOLUTION IS FOR UNSEASONABLY
HOT CONDITIONS THROUGH THE MIDDLE OF NEXT WEEK. THE HOTTEST DAY AT
THIS POINT IN TIME LOOKS TO BE ON SATURDAY. THIS IS WHEN 850-HPA
TEMPERATURE CLIMB ABOVE +21C (>99TH PERCENTILE OF CLIMATOLOGY). THE
EFI ALSO PEAKS OUT ON SATURDAY, SHOWING 0.8-0.9 VALUES, HELPING
ILLUSTRATE THE STRONG CONSENSUS TO THIS ANOMALOUS HEAT. THERE IS A
PRETTY GOOD SIGNAL FOR MORE WIDESPREAD DIURNAL CUMULUS HOWEVER,
WHICH COULD PUT A BIT OF A LID ON HIGHS. REGARDLESS, WIDESPREAD MID
90S ARE EXPECTED ON SATURDAY, WITH A FEW SPOTS POTENTIALLY GETTING
INTO THE UPPER 90S IF THE DIURNAL CUMULUS DEVELOPS LATER IN THE DAY
AND IS MORE FEW VS. SCATTERED/BROKEN IN NATURE. THE HUMIDITY WILL
ALSO BE HIGH ENOUGH TO YIELD HEAT INDEX VALUES A BIT ABOVE THE
AMBIENT AIR TEMPERATURE BOTH SATURDAY AND SUNDAY. SOME SPOTS SHOULD
TOP OUT NEAR 100 DEGREES BOTH OF THESE DAYS FOR PEAK HEAT INDEX
VALUES. WHILE THIS HEAT EVENT SHOULD FALL WELL SHORT OF ADVISORY
CRITERIA (105+ ANY DAY OR 4 DAYS STRAIGHT OF 100+ HEAT INDEX),
THE PAST 2-3 WEEKS HAVE LARGELY FEATURED BELOW TO WELL-BELOW
NORMAL TEMPERATURES. THIS HEAT (AND SOME INCREASE IN HUMIDITY)
WILL BE QUITE THE SHOCK TO MANY AND BE A THREAT TO VULNERABLE
POPULATIONS.
TEMPERATURES SHOULD EVER SO SLIGHTLY COOL THEREAFTER MORE
INTO THE UPPER 80S TO LOW 90S. THIS COMES IN RESPONSE TO SLIGHTLY
COOLER 850-HPA TEMPERATURES AS WELL AS AN INCREASE IN DIURNAL
CUMULUS AND HIGH-LEVEL CLOUDS. IN ADDITION, WITH INCREASING HUMIDITY
(DEWPOINTS) AND INSTABILITY EACH DAY AND WEAK/NO CAPPING (700-HPA
TEMPERATURES < 10C), THERE IS AN INCREASING THREAT FOR AT LEAST
ISOLATED SHOWERS AND THUNDERSTORMS. THIS THREAT SHOULD HOLD OFF
UNTIL THE MORE APPRECIABLE HUMIDITY/INSTABILITY MOVES INTO THE AREA,
BUT WE COULD SEE SOME ACTIVITY AS EARLY AS SATURDAY. THE LREF SHOWS
6-HOUR PROBABILITIES IN THE 10-15% RANGE SATURDAY AFTERNOON, BUT
INCREASES MORE INTO THE 30-40% RANGE SUNDAY/MONDAY BEFORE DROPPING
BACK MORE INTO THE 20-30% RANGE TUESDAY/WEDNESDAY. GIVEN THE PATTERN
AND THE SIGNAL IN ENSEMBLE DATA, DID ADD SLIGHT CHANCE POPS (~20%)
TO BOTH SUNDAY AND MONDAY AFTERNOONS. BRIEF HEAVY DOWNPOURS AND
LIGHTNING WOULD BE THE MAIN THREATS.
GOSSELIN
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 940 PM CDT WED SEP 10 2025
DRY AND VFR FLIGHT CONDITIONS ARE MOST LIKELY THROUGH THE TAF AT ALL
TERMINALS. THERE IS A LOW CHANCE OF RIVER VALLEY FOG AT KSUS AND
KJEF EARLY THURSDAY MORNING, BUT THE PRESENCE OF MID-LEVEL CLOUDS AT
TIMES KEEPS CONFIDENCE INSUFFICIENT FOR INCLUSION. LIGHT WINDS WILL
PREVAIL.
PFAHLER
CLIMATE
ISSUED AT 218 PM CDT WED SEP 10 2025
RECORD DAILY HIGHS FRIDAY 9/12 THROUGH MONDAY 9/15:
9/12 | 9/13 | 9/14 | 9/15
STL 98 100 101 101
COU 100 99 104 101
UIN 99 100 99 100
DELIA
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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