873
FXUS63 KLSX 091739
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
1239 PM 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 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1223 PM CDT SAT AUG 9 2025
THERE WILL BE A CHANCE OF THUNDERSTORMS OVER CENTRAL MISSOURI THAT
COULD AFFECT COU/JEF/UIN LATE THIS AFTERNOON AND THIS EVENING, BUT
CONFIDENCE IS TOO LOW TO INCLUDE IN THE TAF AT THIS TIME. BETTER
CHANCES FOR SHOWERS AND THUNDERSTORMS WILL OCCUR LATE TONIGHT AND
SUNDAY MORNING AT THESE SAME TERMINALS, SO I HAVE INCLUDE PROB30
GROUPS TO ACCOUNT FOR THIS. THERE WILL ALSO BE SCATTERED
THUNDERSTORMS AROUND THE ST. LOUIS AREA TERMINALS AFTER 12Z
TOMORROW, BUT ONCE AGAIN, CONFIDENCE IS TOO LOW TO INCLUDE IN THE
TAFS. ANY OF THE HEAVIER SHOWER AND THUNDERSTORMS COULD PRODUCE
VFR/POSSIBLE IFR CEILINGS AND VISIBILITIES. OTHERWISE, DRY AND VFR
CONDITIONS ARE EXPECTED OUTSIDE OF THUNDERSTORMS. WINDS WILL
GENERALLY BE OUT OF THE SOUTH THROUGH THE PERIOD.
BRITT
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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