219
FXUS63 KLSX 081729
AFDLSX
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
1229 PM CDT FRI AUG 8 2025
KEY MESSAGES
- HOT AND HUMID CONDITIONS ARE EXPECTED THIS WEEKEND WITH A CHANCE
FOR SHOWERS AND THUNDERSTORMS LATE SATURDAY AFTERNOON INTO
SATURDAY NIGHT AND SUNDAY, MAINLY ALONG AND NORTH OF I-70.
- THE CHANCE FOR SHOWERS AND THUNDERSTORMS INCREASES INTO NEXT
WEEK. THIS WILL BRING COOLER TEMPERATURES TO THE AREA, ALTHOUGH
IT WILL STILL BE NEAR NORMAL FOR EARLY AUGUST.
SHORT TERM
(THROUGH SATURDAY NIGHT)
ISSUED AT 352 AM CDT FRI AUG 8 2025
PRIMARY FORECAST CONCERN FOR TODAY AND SATURDAY IS THE POTENTIAL
FOR ADVISORY CRITERIA HEAT. A CLOSED LOW WILL MOVE SLOWLY ALONG
THE US/CANADA BORDER TODAY AND SATURDAY. THE TROUGH ASSOCIATED
WITH THIS LOW EXTENDS SOUTH ACROSS MONTANA AND WYOMING THIS
AFTERNOON, AND IS FORCING LOW LEVEL CYCLOGENESIS OVER THE GREAT
PLAINS. THIS WILL PRODUCE WARM LOW LEVEL SOUTH-SOUTHWEST FLOW
TODAY WHICH WILL PERSIST INTO THE WEEKEND. LATEST NBM IS SHOWING
HIGHS CLIMBING UP INTO THE LOW TO MID 90S ACROSS THE AREA. THIS
FITS PRETTY WELL WITH SHORT RANGE DETERMINISTIC 850MB TEMPS WHICH
RISE INTO THE 20-22C RANGE THIS AFTERNOON. NBM DEW POINT
TEMPERATURES ON THE OTHER HAND LOOK TOO HIGH. FORECAST SOUNDINGS
SHOW DEEP MIXING UP TO 800MB+ ACROSS MOST OF THE AREA. SOUNDINGS
ALSO SHOW A RELATIVELY DRY ATMOSPHERE ALOFT, SO THE DEEP MIXING
SHOULD LOWER AFTERNOON DEW POINT TEMPERATURES, PARTICULARLY ALONG
AND SOUTH OF I-70 WHERE SOUNDINGS INDICATE THE DEEPEST MIXING.
NORTHEAST MISSOURI INTO WEST CENTRAL ILLINOIS SHOULD SEE THE
SHALLOWEST MIXING AND WILL PROBABLY HAVE THE HIGHEST DEW POINT
TEMPERATURES. THAT SAID, THERE SHOULD STILL BE SOME DRIER AIR
MIXING DOWN SO NBM DEW POINT TEMPERATURES ARE LIKELY STILL 2-3
DEGREES TOO HIGH. ALL THIS FALLS OUT TO WHAT WILL BE A SEASONABLY
HOT AND HUMID DAY, THOUGH NOT EXCESSIVELY SO. CONDITIONS WILL BE
VERY SIMILAR ON SATURDAY AS THE GREAT PLAINS TROUGH MAKES ONLY
VERY SLOW EASTWARD PROGRESS. THERE COULD ALSO BE SOME
THUNDERSTORMS SATURDAY AFTERNOON ACROSS NORTHEAST MISSOURI INTO
WEST CENTRAL ILLINOIS, AND THIS WOULD BE THE MOST LIKELY AREA TO
HIT MARGINAL HEAT ADVISORY CRITERIA ON SATURDAY. AS A BRIEF
ASIDE, GUIDANCE IS SHOWING UP TO AROUND 3000 J/KG MLCAPE SATURDAY
AFTERNOON/EVENING, SO THERE IS POTENTIAL FOR A FEW STRONG/SEVERE
STORMS. HOWEVER, DEEP LAYER SHEAR IS ONLY IN THE 20-25KT RANGE, SO
THE THREAT SHOULD BE LIMITED. BACK TO THE HEAT, THE POTENTIAL FOR
CONVECTION THEREFORE ADDS ADDITIONAL UNCERTAINTY TO THE
TEMPERATURE FORECAST. LATEST FORECAST HEAT INDEX VALUES TOP OUT
BETWEEN 100-104 TODAY, AND JUST KISS 105 IN A FEW SPOTS ON
SATURDAY, SO WILL HOLD OFF ISSUING AN ADVISORY AT THIS TIME.
CARNEY
LONG TERM
(SUNDAY THROUGH THURSDAY)
ISSUED AT 352 AM CDT FRI AUG 8 2025
MEDIUM RANGE GUIDANCE IS GENERALLY IN GOOD AGREEMENT SHIFTING THE
PATTERN EASTWARD NEXT WEEK. THE MID-UPPER LEVEL TROUGH OVER THE
GREAT PLAINS WILL MOVE ACROSS THE MIDWEST BY MIDWEEK AND THE UPPER
RIDGE OVER THE SOUTHWEST WILL BUILD BACK TOWARD THE MID MISSISSIPPI
VALLEY TOWARD THE END OF THE PERIOD. FOR SUNDAY THROUGH WEDNESDAY
THIS WILL TRANSLATE INTO (MAINLY) AFTERNOON AND EVENING CHANCES FOR
CONVECTION, AND TEMPERATURES A FEW DEGREES LOWER. HIGHS WILL
LARGELY BE CONTROLLED BY HOW MUCH CONVECTION THERE IS AND WHERE IT
ULTIMATELY TRACKS. THIS WILL BE PARTICULARLY TRUE ON TUESDAY WHEN
THE TROUGH WILL BE MOVING INTO THE MID MISSISSIPPI VALLEY AND
SCATTERED TO POTENTIALLY NUMEROUS SHOWERS AND STORMS ARE MOST
LIKELY. THURSDAY LOOKS DRIER AND WARMER AS THE UPPER RIDGE BUILDS
IN BEHIND THE TROUGH.
CARNEY
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1228 PM CDT FRI AUG 8 2025
DRY/VFR CONDITIONS ARE FORECAST THROUGH SATURDAY MORNING ALONG
WITH DRY WEATHER. SOUTHERLY WINDS WILL WEAKEN SLIGHTLY THIS
EVENING INTO THE OVERNIGHT BEFORE PICKING BACK UP CLOSER TO 10
KNOTS WITH SOME PERIODIC GUSTS AT KCOU/KUIN AGAIN BY LATE
SATURDAY MORNING.
GOSSELIN
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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