Area Forecast Discussion

257
FXUS63 KLSX 192337
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
637 PM CDT Sun Oct 19 2025

.KEY MESSAGES...

- Cooler and drier weather is expected this week with the
  potential for frost midweek.

- Rain chances return at the end of the week.


&&

.SHORT TERM... (Through Monday Night)
Issued at 221 PM CDT Sun Oct 19 2025

Quite a difference a day makes. Yesterday was rain and stormy for
much of the area, the last gasps of a warm and humid late season
air mass. But after last night`s frontal passage we`re enjoying a
clear blue sky today with cool temperatures and much drier air.
Dewpoints have fallen into the 30s area wide, even a bit drier
than expected.

A progressive flow pattern will quickly usher pressure systems
across the country the next few days leading to windier conditions
than we`ve seen in a while. High pressure building through the
Southern Plains behind this morning`s front has led to the breezy
northwest winds today. As that high pressure axis shifts east
tonight we`ll see winds die off considerably this evening, though
maybe not to completely calm. We should see good enough cooling
conditions for widespread lows in the 40s tonight, but a light
westerly flow across the top of the surface high should prevent
temperatures from getting much cooler. It should also limit the
potential for fog. But tomorrow the high moving east and another
cold front approaching from the west cranks the winds back up
again, this time out of the south/southwest. That will allow our
temperatures to bounce back a bit, into the 70s, but moisture
return from the Gulf is blocked so we don`t really get any good
rain chances as the front approaches Monday night.

Kimble

&&

.LONG TERM...  (Tuesday through Next Sunday)
Issued at 221 PM CDT Sun Oct 19 2025

Monday night`s front brings an even cooler and even drier air mass
behind it. Expect another day of gusty winds on Tuesday ushering
that air mass in, but eventually the surface high moves across our
region bringing a period of calm. Guidance has gradually slowed
down the passage of this surface high so that it will bring the
best period of calm conditions Wednesday night into Thursday
morning when we are likely to see our coldest temperatures.
Dewpoints in the 30s or even upper 20s suggest the floor for
temperatures is even lower in this air mass. Latest NBM forecasts
most locations getting into the 30s outside of the St Louis urban
environment. If we do see a full night of clear, calm conditions
it could be even colder with the potential for some protected
valleys getting near the freezing mark for the first time this
year.

Upper flow pattern late this week features a large ridge in the
northern stream but a trough in the southern stream slowly moving
out of the Southwest US into the Southern Plains. The building
ridge and the return flow on the back of the surface high will
allow for some modest warming from our cold midweek temperatures.
The approaching trough will grab some Gulf moisture and bring our
next chance of rain. Guidance has gradually been honing in on late
Friday into Saturday as the most likely time for rain in our area
and NBM PoP has indeed increased during this time frame. Among the
long range ensemble guidance, 70 to 80 percent produce rain across
southern MO into southern IL during this time period so we`re
fairly confident that we`ll see some rain out of this even with
the lingering timing uncertainty. With our area on the northern
side of this wave we`ll see a winter-type synoptic driven light
rainfall. Up to 30 percent of guidance produces 0.5 inch or more
of rain. The greater confidence in this system has also led to
some cooler forecast temperatures Friday into Saturday as clouds
and rain would hold temperatures down even further. Once this
system moves out the modest warm up resumes.

Kimble

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 636 PM CDT Sun Oct 19 2025

VFR flight conditions will prevail through the period. Wind will
back to the south overnight and become gusty Monday morning. Could
see gusts to around 30kts late Monday morning into the afternoon.

Carney

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion