937 FXUS63 KLSX 032240 AFDLSXArea Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 540 PM CDT Fri Oct 3 2025
.KEY MESSAGES...
- The ongoing warmth will continue through early next week until a cold front cools us off by mid-week.
- A cold front will bring our highest chance of showers and thunderstorms for the next week on Monday and Tuesday (30 - 40%).
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.SHORT TERM... (Through Late Saturday Night) Issued at 238 PM CDT Fri Oct 3 2025
Scattered showers and thunderstorms continue to percolate this afternoon due to SBCAPE of 1000 - 1500 J/kg and weak mid-level lift. This convection has produced much needed rain for a lucky few, with very localized MRMS estimates of 2"+ in portions of southern Illinois so far. Unfortunately, daytime instability will diminish with sunset, and so will our rain chances through the weekend as mid- level ridging dominates our sensible weather.
Low-level ridging in the eastern CONUS will usher cooler and drier 850 mb air into the region tomorrow. The new advection will result highs a few degrees cooler than today despite abundant sunshine and a warm morning.
Jaja
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.LONG TERM... (Sunday through Next Friday) Issued at 238 PM CDT Fri Oct 3 2025
The mid-level ridge will exit east through the weekend as a deep mid- level trough shoves into south-central Canada/the Upper Midwest by Monday. This will allow access to Gulf moisture on Monday, which coincides with the approach of a cold front from the northwest. Incoming vort maxes aloft overlapping with the new-found moisture will support at least some potential for the showers and thunderstorms during the day in our southern and eastern counties. That night, additional showers and thunderstorms will push into northeast Missouri and west-central Illinois along the cold front. Although there is high confidence in the aforementioned features bringing us much needed rain with LREF probabilities showing a 70 to 80% chance of measurable rain. Significant rain, on the other hand, is not likely. The same run has probabilities of 0.25" peaking at 30% with most locations under 25%.
A rush of cold air will follow the cold front, dropping high temperatures from widespread 80s on Monday to widespread 70s by Wednesday. NBM highs for Wednesday are warmer than they initialized 24 hours ago, suggesting the broad trough responsible for the cold front may not be as influential as once thought. Despite this, a walk back into the 70s for Wednesday and Thursday will be an appreciated break from the heat before low-level warm air advection and subsequent warmth returns by next weekend.
Jaja
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.AVIATION... (For the 00z TAFs through 00z Saturday Evening) Issued at 537 PM CDT Fri Oct 3 2025
While a few weak showers and weak thunderstorms continue to percolate as of 2230Z, the majority of this activity is expected to diminish by the beginning of the 00Z TAF period, and additional impacts are not expected.
Otherwise, VFR conditions are expected the remainder of the period. Prevailing southerly winds will become somewhat breezy by late morning and continue for the remainder of the day. While we can`t completely rule out some more brief fog near sunrise at SUS and CPS if winds become calm in the river valley, confidence in this occurring is too low to include in the TAF at this time.
BRC
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.LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. &&
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WFO LSX
NWS LSX Office Area Forecast Discussion