109
FXUS63 KLSX 082330
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
630 PM CDT Wed Oct 8 2025

.KEY MESSAGES...

- Mostly dry weather will persist through at least this weekend.

- A warming trend will kick off Friday with highs in the 80s
  beginning Saturday.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 300 PM CDT Wed Oct 8 2025

Surface high pressure currently centered over the Upper Midwest will
push into New England by Thursday night. Despite the high never
centering directly over the CWA, this feature will still have enough
influence to keep both high and low temperatures dampened through
the short term. With cold, dry air settled into the Mid-Mississippi
Valley and efficient radiational cool conditions expected tonight,
lows will tank into the upper 30s to low 40s. Low-lying and
sheltered areas will see the brunt of the cold and can expect to
fall a degree or two cooler than our forecast lows. Conditions will
be more favorable for at least steam fog tonight given the cooler
air and position relative to the surface high. Expect patchy fog
again, especially in river valleys. Similar conditions are expected
for most of the area tomorrow night. The exception will be west-
central Illinois through central Missouri as increased cloud cover
will impede radiational cooling.

In the interim, a cool start to the morning and ongoing cold air
advection will keep high temperatures near average again tomorrow
afternoon. Expect highs in the low to mid-70s with very little
humidity.

Jaja

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 300 PM CDT Wed Oct 8 2025

A mid-level closed low will shunt southeastward through the Great
Lakes late this week, dragging a cold front through the Upper
Midwest. Ahead of this feature in the Mid to Upper Mississippi
Valley, southerly low-level flow, warm air advection, and meager
moisture return will establish itself Thursday night into early
Friday morning. The increase in warmth and moisture may provide
enough instability for elevated showers and thunderstorms Friday
morning in portions of west-central Illinois southwestward through
central Missouri. The mitigating factor to any precipitation will be
moisture return. Without sufficient moisture, 1) instability will be
lacking and 2) anything that does develop will be quickly snuffed
out by the dry environment they`ll exist in. The latest ensembles
suggest there may be a middle ground in which there is enough
moisture to promote elevated convection but not enough to sustain it
for long. This is represented by an increase to a 45 - 80%
probability of measurable rain on Friday with a relatively tight
gradient decreasing from west to east. If it does rain, these same
probabilities only call for a 20 - 30% chance of >0.1" of 24 hour
precipitation, so it will not be beneficial. This is our greatest
chance of rain through at least this weekend.

The same warm air advection promoting rain chances on Friday will
aid in our return to above normal warmth Friday through early next
week. Mid-level ridging will dominate our sensible weather, allowing
us to heat without the threat of precipitation at least through the
weekend. Precipitation chances do increase slightly again early next
week as shortwaves ride the ridge into the Mid-Mississippi Valley,
but differences in the timing, strength, and location of these
features preclude high confidence in any one solution.

Jaja

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 628 PM CDT Wed Oct 8 2025

River valley steam fog is the biggest concern overnight. KSUS and
KJEF along the Missouri are the most likely terminals to see
impacts, with IFR visibilities expected. VLIFR conditions are also
possible within an hour or two of dawn. Outside of the fog,
dry/VFR conditions are expected through Thursday afternoon.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX