459
FXUS63 KLSX 120848
AFDLSX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAINT LOUIS MO
348 AM CDT TUE AUG 12 2025
KEY MESSAGES
- A THREAT FOR SCATTERED THUNDERSTORMS WILL CONTINUE TODAY ACROSS
PARTS OF THE REGION, PARTICULARLY IN SOUTHEAST MO AND SOUTHWEST
IL. GUSTY WINDS AND LOCALLY-HEAVY RAIN ARE THE MAIN THREATS.
- RAIN CHANCES WANE THROUGH MID-WEEK AS HOT, MUGGY CONDITIONS
GRADUALLY BUILD INTO THE REGION LATE THIS WEEK INTO THE WEEKEND.
SHORT TERM
(THROUGH LATE WEDNESDAY AFTERNOON)
ISSUED AT 348 AM CDT TUE AUG 12 2025
AN AMPLIFIED WAVE ALOFT EVIDENT ON GOES MID-LEVEL WATER VAPOR
IMAGERY IS CURRENTLY CENTERED OVER THE PLAINS AND MEANDERING EAST
INTO THE MID-MISSISSIPPI VALLEY. EARLIER STRONG TO SEVERE
THUNDERSTORMS, FORCED SOMEWHAT BY THIS MID-LEVEL FEATURE, ARE NOW
FAR TO THE NORTH AND EAST OF THE REGION. IN THEIR WAKE, RAIN-COOLED
AIR BEHIND AN OUTFLOW BOUNDARY SEVERELY HAMPERED ANY LINGERING
INSTABILITY ACROSS MOST OF THE FORECAST AREA. THAT, ALONG WITH A
WEAK LOW-LEVEL JET, IS RESULTING IN A LARGELY TRANQUIL NIGHT ACROSS
THE BI-STATE. THE MID-LEVEL TROUGH AXIS WILL TRANSLATE EAST THIS
MORNING AND, ALONG WITH WEAK SURFACE CONVERGENCE EVIDENT IN A FEW
HIGHER-RESOLUTION MODELS, SERVE AS THE FOCUS FOR ADDITIONAL SHOWERS
AND THUNDERSTORMS THIS AFTERNOON AND EVENING. THE MOST ROBUST
UPDRAFTS AND SLIGHTLY STRONGER 0-3KM SHEAR WILL BE RELEGATED TO OUR
NORTHEAST WHERE UPPER-LEVEL ASCENT IS STRONGER, KEEPING ANY
ORGANIZED SEVERE WEATHER THREAT AT BAY. THAT SAID, A FEW STRONGER
CORES THIS AFTERNOON MAY RESULT IN 30-45MPH WINDS, PARTICULARLY
ALONG AND SOUTH OF I-44. WITH ABNORMALLY-HIGH PRECIPITABLE WATER
VALUES STILL IN PLACE AND STORM MOTIONS SOMEWHAT PARALLEL TO THE
BOUNDARY, A FEW INSTANCES OF MINOR FLOODING WOULDN'T SHOCK ME EITHER.
WHILE MOST DETERMINISTIC GUIDANCE SHOWS THE TROUGH FLATTENING AND
SLOWING DOWN OVER OUR REGION, THE TROUGH AXIS MAKES SLOW, STEADY
PROGRESS EASTWARD AND EVENTUALLY EXISTS. IT ALSO DRAWS A WEAK COLD
FRONT THROUGH THE REGION THROUGH WEDNESDAY MORNING, ALLOWING FOR
SLIGHTLY-COOLER AND DRIER AIR TO FILTER SOUTH. THE BOUNDARY STALLS
SOMEWHERE BETWEEN THE OZARKS AND THE TENNESSEE/MISSISSIPPI BORDER.
THE UNCERTAINTY SURROUNDING THE FRONT'S SOUTHWARD PROGRESS WILL
LEAVE A LOW (15-20%) CHANCE FOR SHOWERS AND THUNDERSTORMS ACROSS
SOUTHERN MISSOURI AND SOUTHERN ILLINOIS ON WEDNESDAY. OTHERWISE,
TEMPERATURES DROP AS MUCH AS 8-10 DEGREES IN SOME SPOTS COMPARED TO
TODAY'S HIGHS BEHIND THE FRONT.
MRB
LONG TERM
(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 348 AM CDT TUE AUG 12 2025
THE BASE OF THE SURFACE RIDGE WILL CONTINUE TO PROMOTE SOMEWHAT
COOL AND DRY CONDITIONS THURSDAY, SIMILAR TO WEDNESDAY. BY EARLY
FRIDAY MORNING THE RIDGE WILL DRIFT EAST AND WARM, HUMID RETURN FLOW
WILL RE-ESTABLISH OVER THE REGION. MOST ENSEMBLE SOLUTIONS AGREE
THAT AN ANOMALOUSLY-STRONG MID-LEVEL RIDGE (EXCEEDING THE 90TH
CLIMATOLOGICAL PERCENTILE) SETTLES RIGHT OVER THE MID-MISSISSIPPI
VALLEY BY SATURDAY, BOLSTERING TEMPERATURES INTO THE MID-90S ALMOST
AREAWIDE. THE NBM INTERQUARTILE RANGE FOR HIGH TEMPERATURES FRIDAY-
SUNDAY IS FAIRLY TIGHT, ONLY 4-5 DEGREES SETTLING AROUND THE MID-
90S, LENDING MORE CONFIDENCE TO THE HOT FORECAST. THE STRONG
SUBSIDENCE ACCOMPANYING THE RIDGE ALOFT WILL ALSO KEEP ANY THREAT
FOR THUNDERSTORMS FAIRLY LOW (10-15% AT MOST THROUGH SUNDAY). SOME
AREAS MAY SEE AIRMASS THUNDERSTORMS IN THE AFTERNOON, BUT IT'S FAR
TOO EARLY TO PINPOINT WHERE THAT WOULD BE.
WHAT I'M LESS CERTAIN OF IS THE LEVEL OF HUMIDITY. WHILE DEWPOINTS
WILL BE FAIRLY HIGH (AT LEAST THE UPPER 60S AREAWIDE) PROMOTING
MUGGY CONDITIONS, THERE IS SOME UNCERTAINTY ABOUT WHERE POTENTIALLY-
DANGEROUS HEAT/HUMIDITY WILL BE. THE 850MB THERMAL RIDGE IS
CONSISTENTLY DEPICTED ACROSS NORTHERN MISSOURI AND WEST-CENTRAL
ILLINOIS THROUGH THE WEEKEND, WHICH MAY ACT TO STRONGLY CAP ANY
DIURNAL INSTABILITY AND KEEP DEWPOINTS HIGH THERE. FURTHER SOUTH,
WHERE MIXING MAY BE A BIT DEEPER, THERE IS MORE UNCERTAINTY IN EXACT
HUMIDITY VALUES THAT MAY HINDER TRULY DANGEROUS CONDITIONS A BIT.
WHILE IT WILL CERTAINLY BE AN UNCOMFORTABLE WEEKEND, THE HIGHEST
POTENTIAL FOR DANGEROUS HEAT LOOKS TO BE OVER NORTHERN MISSOURI AND
WEST-CENTRAL ILLINOIS.
THERE'S SOME MILD AGREEMENT THAT THE STRONG RIDGING BREAKS DOWN BY
EARLY NEXT WEEK, AND WHILE THE TREND WILL BE SLIGHTLY COOLER AND A
BIT MORE ACTIVE PRECIPITATION-WISE, NOTHING STANDS OUT AS
PARTICULARLY THREATENING AT THIS POINT FOR THE MID-MISSISSIPPI
VALLEY.
MRB
AVIATION
(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1057 PM CDT MON AUG 11 2025
PRIMARY FORECAST CONCERN IS FOR THUNDERSTORM DEVELOPMENT ALONG A
FRONT MOVING IN FROM THE WEST. STORMS CURRENTLY ONGOING OVER
NORTHEAST MO ARE LIKELY TO MISS ANY TAF SITE, ALTHOUGH QUINCY HAS
AN OUTSIDE SHOT AT A TS IN THE NEXT COUPLE OF HOURS. OTHERWISE
STORMS REDEVELOP NEAR THE FRONT EARLY TUESDAY AFTERNOON IN THE ST
LOUIS AREA. OUTSIDE OF STORMS, WINDS ARE FAIRLY LIGHT AND VFR
CONDITIONS ARE EXPECTED.
KIMBLE
LSX WATCHES/WARNINGS/ADVISORIES
MO...NONE.
IL...NONE.
WFO LSX
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