925 FXUS63 KLSX 151056 AFDLSXArea Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 556 AM CDT Mon Sep 15 2025
.KEY MESSAGES...
- Hot weather is expected through Thursday with some relief likely by the end of the week.
- There is a chance of thunderstorms over parts of the area each day, with the best chance (30-60%) across much of the area Thursday night into Saturday.
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.SHORT TERM... (Through Late Tuesday Afternoon) Issued at 331 AM CDT Mon Sep 15 2025
Scattered thunderstorms currently drifting over central and southeast Missouri will likely dissipate in the next few hours as the RAP is showing low level convergence weakening. The rest of the morning is expected to be mainly dry before additional scattered showers and thunderstorms (20-30% chance) develop by early afternoon across the western half of the CWA. These storms will occur on the western periphery of the upper ridge where the RAP is showing some surface convergence this afternoon. Like yesterday, I could not rule out one or two stronger wind gusts this afternoon (>45 mph) with these storms given MLCAPES in the 2000-3000+ J/kg range and inverted-V soundings seen in the RAP. The storms will die out by early this evening with the loss of daytime heating leaving the rest of tonight dry.
With current temperatures in the 70s, highs today will still climb into the low to mid 90s. Lows tonight will drop into the 60s.
Britt
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.LONG TERM... (Tuesday Night through Sunday) Issued at 331 AM CDT Mon Sep 15 2025
The LREF is showing that the upper high associated with the omega block will stay in place through Thursday which will continue to keep forcing for daily scattered showers and thunderstorms confined over the western part of the CWA. The omega block will begin to break down later this week as the western upper trough moves east across the Midwest increasing the chance of showers and thunderstorms areawide. 30-60% of the LREF members are producing precipitation across CWA Thursday night into Saturday supporting this trend.
With the omega block staying in place, still expect highs to be mainly in the 90s through Thursday before dropping back into the 80s and upper 70s as 850mb temperatures fall from 20C to 15C. Temperatures will also be affected by more clouds and the potential for clouds and rain. This is reflected in the NBM IQR at STL which is only 2-4 degrees through Thursday but then increases to 7 degrees from Friday on.
Britt
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.AVIATION... (For the 12z TAFs through 12z Tuesday Morning) Issued at 546 AM CDT Mon Sep 15 2025
There will be scattered thunderstorms that may affect UIN/COU/JEF this afternoon and have added PROB30 groups at COU/JEF between 21-24Z where I think the location and timing is most likely. If thunderstorms do affect a terminal, MVFR/possible IFR ceilings and visibilites are possible in brief downpours. Otherwise dry and VFR conditions are expected with light winds outside of thunderstorms.
Britt
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.LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. &&
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WFO LSX
NWS LSX Office Area Forecast Discussion