034
FXUS63 KLSX 091054
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
554 AM CDT SAT AUG 9 2025
KEY MESSAGES
- IT WILL BE HOT AND HUMID AGAIN TODAY, WITH HEAT INDEX VALUES TOPPING
OUT AROUND 100 DEGREES IN MOST LOCATIONS.
- THE CHANCE FOR SHOWERS AND THUNDERSTORMS INCREASES TONIGHT,
MAINLY ACROSS NORTHEAST MISSOURI INTO WEST CENTRAL ILLINOIS.
LOCALLY HEAVY RAINFALL WILL BE POSSIBLE IF STORMS TRACK OVER THE
SAME LOCATIONS, ALTHOUGH CONFIDENCE IN HEAVY RAINFALL THROUGH
SUNDAY MORNING IS LOW AT THIS TIME.
SHORT TERM
(THROUGH LATE TONIGHT)
ISSUED AT 404 AM CDT SAT AUG 9 2025
WEAK SHOWERS STRETCHING FROM SOUTHWEST MISSOURI UP THROUGH CENTRAL
AND NORTH CENTRAL MISSOURI APPEAR TO BE DRIVEN BY AN AREA OF MID-
LEVEL VORTICITY STRETCHING ACROSS THE STATE. THE MID-LEVEL NATURE
OF THE FORCING APPEARS TO BE CONFIRMED BY A CALL TO KMHL WHICH IS
SHOWING OVERCAST ON SATELLITE BUT THE AWOS IS REPORTING CLEAR BELOW
12,000. SHORT RANGE GUIDANCE KEEPS MOST OF THIS ACTIVITY WEST OF
THE CWFA, THOUGH A FEW SHOWERS COULD STRAY INTO PARTS OF CENTRAL AND
NORTHEAST MISSOURI BEFORE THEY DISSIPATE LATER THIS MORNING.
OTHERWISE, EXPECT TODAY TO BE MUCH LIKE YESTERDAY WITH PERSISTENT
SOUTHERLY FLOW DUE TO HIGH PRESSURE OVER THE EASTERN U.S. AND A
TROUGH APPROACHING FROM THE GREAT PLAINS. EXPECT HIGHS IN THE LOW
TO MID 90S AGAIN WITH MAX HEAT INDEX VALUES AROUND 100.
ATTENTION TURNS TO THE POTENTIAL FOR THUNDERSTORMS AND HEAVY RAIN
TONIGHT. THE AFOREMENTIONED TROUGH OVER THE GREAT PLAINS IS PUSHING
A COLD FRONT INTO IOWA, SOUTHEAST NEBRASKA, AND NORTHEAST/NORTH
CENTRAL KANSAS TODAY. SHORT RANGE DETERMINISTIC GUIDANCE IS SHOWING
MLCAPE BETWEEN 3500-4500 J/KG AHEAD OF THE FRONT ACROSS SOUTHERN
IOWA AND PARTS OF NORTHERN MISSOURI THIS AFTERNOON/EVENING. MODELS
ALSO SHOW AS MUCH AS 100-200 J/KG CINH SOUTH OF THE FRONT THIS
AFTERNOON AND EVENING. CURRENT THINKING THEREFORE IS THAT THE BEST
CHANCE FOR THUNDERSTORM DEVELOPMENT WILL BE IN THE VICINITY OF THE
FRONT EITHER LATE THIS AFTERNOON OR INTO THE EVENING ACROSS
NORTHWEST MISSOURI INTO SOUTHERN IOWA. THINK THE MOST LIKELY
SCENARIO IS THAT CONVECTION GROWS QUICKLY UPSCALE INTO AN MCS.
FORWARD PROPAGATING CORFIDI VECTORS INDICATE AN EAST OR EVEN EAST-
NORTHEAST MOVEMENT OF AN MCS. ADDITIONALLY, THE LOW LEVEL JET WILL
BE FOCUSED OVER NORTHWEST MISSOURI INTO SOUTHERN IOWA ON SATURDAY
NIGHT, WHICH SHOULD TEND TO KEEP THUNDERSTORMS AND THE HEAVIEST RAIN
OVER THOSE LOCATIONS AND (MOSTLY) OUT OF OUR CWFA. THAT SAID, PARTS
OF NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS COULD GET CLIPPED BY
THE TAIL END OF THE MCS WITH STRONG TO SEVERE WIND GUSTS. THE CAMS
SHOW LITTLE CONSISTENCY, EITHER RUN-TO-RUN OR BETWEEN MODELS. MOST
FOCUS THE STRONGEST CONVECTION ACROSS NORTHERN MISSOURI INTO IOWA,
BUT SOME (MOST NOTABLY THE WRF-ARW CORE) BRING THUNDERSTORMS WITH
HEAVY RAIN AS FAR SOUTH AS I-70 OVERNIGHT. I THINK THIS IS AN
OUTLIER AS THE DETERMINISTIC GUIDANCE BARELY HAS ANY RAIN, LET ALONE
HEAVY RAIN, IN OUR AREA BEFORE 12Z SUNDAY. HAVE THEREFORE HELD OFF
ISSUING ANY FLOOD WATCHES THIS SHIFT. HOWEVER, THE SITUATION SHOULD
BE MONITORED CLOSELY IN CASE THE FRONT MAKES IT FARTHER SOUTHEAST
INTO MISSOURI WHICH WOULD CHANGE THE TRACK OF THE MCS.
CARNEY
LONG TERM
(SUNDAY THROUGH FRIDAY)
ISSUED AT 404 AM CDT SAT AUG 9 2025
THE MID-UPPER LEVEL TROUGH DRIVING THE SURFACE FRONT MOVES SLOWLY
ACROSS THE MIDWEST THROUGH THE MIDDLE OF NEXT WEEK. THIS WILL
PRODUCE ONLY WEAK SYNOPTIC FORCING TO MOVE THE COLD FRONT TO THE
EAST, AND THE EFFECTIVE BOUNDARY WILL LIKELY BE CONTROLLED MORE BY
THUNDERSTORM OUTFLOW THAN FORCING PROVIDED BY THE TROUGH. THEREFORE
THE PRECIPITATION AND TEMPERATURE FORECASTS FOR NEXT WEEK ARE LOW
CONFIDENCE AT THIS TIME. IN GENERAL, THE FRONT SHOULD MOVE EAST-
SOUTHEAST SUNDAY THROUGH WEDNESDAY, LIKELY MAKING MORE FORWARD
PROGRESS THROUGH THUNDERSTORM ACTIVITY DURING THE EVENING AND
OVERNIGHT, AND THEN DRIFTING A BIT BACK TO THE NORTH-NORTHWEST
DURING THE DAY DUE TO PERSISTENT SOUTHERLY FLOW FROM HIGH PRESSURE
OVER THE EASTERN U.S./WEST ATLANTIC. AFTERNOON HIGHS SHOULD COOL
INTO THE MID 80S TO AROUND 90 DUE TO INCREASED CLOUDS AND CONVECTION
BY MONDAY-TUESDAY. ENSEMBLE GUIDANCE IS SHOWING MEAN P-WATS IN THE
1.7-1.85 RANGE WITH THE 75TH PERCENTILE UP TO AROUND 2 INCHES.
THEREFORE THERE WILL CERTAINLY BE PLENTY OF MOISTURE AVAILABLE TO
PRODUCE HEAVY RAINFALL THROUGH THE PERIOD AND THE SLOW MOVEMENT OF
THE FRONT WILL INCREASE THE CHANCE THAT THUNDERSTORMS WILL AFFECT
THE SAME LOCATIONS FOR SEVERAL DAYS IN A ROW. FLASH FLOODING/RIVER
FLOODING WILL THEREFORE BE POSSIBLE UNTIL THE FRONT MOVES OUT OF THE
AREA...MOST LIKELY LATE WEDNESDAY INTO THURSDAY.
CARNEY
AVIATION
(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 545 AM CDT SAT AUG 9 2025
VFR FLIGHT CONDITIONS AND SOUTHERLY FLOW ARE EXPECTED TO PREVAIL
ACROSS THE AREA AT LEAST UNTIL LATE THIS AFTERNOON. THERE IS A
CHANCE THAT THUNDERSTORMS WILL AFFECT PARTS OF NORTHEAST MISSOURI
AND WEST CENTRAL ILLINOIS LATE THIS AFTERNOON INTO THE EVENING
HOURS. THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS IOWA DURING
THE AFTERNOON OR EARLY EVENING, AND MAY EXTEND AS FAR SOUTH AS
NORTHERN MISSOURI INTO CENTRAL ILLINOIS. IF THUNDERSTORMS DO
AFFECT NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS THEY WILL BE
CAPABLE OF LOWERING VISIBILITIES TO LESS THAN 2SM IN HEAVY
DOWNPOURS, AND PRODUCING WIND GUSTS UP TO 50KTS. ANOTHER ROUND OF
STORMS WILL BE POSSIBLE ACROSS NORTHEAST MISSOURI INTO WEST
CENTRAL ILLINOIS AFTER 06Z, AND THESE STORMS MAY EXTEND INTO
CENTRAL MISSOURI BEFORE 12Z.
CARNEY
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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