Valmeyer, Illinois Weather Forecast Discussion

580
FXUS63 KLSX 251918
AFDLSX
Area Forecast Discussion
National Weather Service Saint Louis MO
218 PM CDT Thu Sep 25 2025
.KEY MESSAGES...
- Dry weather with seasonably warm daytime temperatures are
  expected over the next 7 days.
&&
.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 218 PM CDT Thu Sep 25 2025
A weak surface ridge of high pressure is expected to build into
the mid-Mississippi Valley tonight with a mid/upper level trough
moving further away into the mid south. Any diurnal
cumulus/stratocumulus should dissipate quickly this evening,
leaving a mostly clear sky for the remainder of the night. A clear
sky with light/variable winds will be very favorable for
radiational cooling. Lows in the low to mid 50s are forecast, or a
degree or two below normal for the date. River valleys in parts
of east central and southeast Missouri should be a bit cooler,
with some spots dropping down into the upper 40s. Speaking of
river valleys, we should see some more steam fog late tonight into
Friday morning given water temperatures observations are
currently in the mid to upper 70s. Any fog should then quickly
evaporate within about 2 hours after sunrise.
Highs on Friday should be at least a couple of degrees warmer than
this afternoon given weak low-level warm air advection and a lack of
any diurnal cumulus/stratocumulus clouds. Readings should top out
right near the 80 degree mark, or about 3-5 degrees above seasonal
averages.
Gosselin
&&
.LONG TERM...  (Friday Night through Next Thursday)
Issued at 218 PM CDT Thu Sep 25 2025
There remains high confidence in a prolonged dry stretch of weather
through next week given a quasi-omega block across the CONUS. The
center of the mid/upper level ridge moves more over the Mississippi
Valley by late this weekend and remains there next week. There is
some uncertainty with how the cutoff low across the southeast CONUS
interacts with the possible tropical cyclone near the southeast
coast, but regardless, our area should remain dry. Probabilities
from the LREF for measurable precipitation over any 24-hour period
through next Thursday never get above 10%.
Daytime temperatures are expected to reach into the low to mid 80s
each day, or about 6-10 degrees above normal. Nighttime lows are
expected to be mostly in the mid 50s, or closer to normal due to a
lack of cloud cover, light winds, and low humidity. Similar to the
chances (or lack thereof) of rainfall, there is also high confidence
in high and low temperatures through at least Tuesday. This is
illustrated well by the very low inter-quartile ranges seen on the
13Z NBM (2-5 degrees). The spread increases for Wednesday and next
Thursday as spread in ensemble guidance increases with respect to
the strength of the surface ridging across the Great Lakes. A
stronger (weaker) ridge could lead to at least slightly cooler
(warmer) temperatures than currently forecast.
Gosselin
&&
.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1200 PM CDT Thu Sep 25 2025
Light northwest winds are forecast to become light/variable this
evening with diurnal cumulus/stratocumulus dissipating. Steam fog
is expected in river valleys late tonight into early Friday
morning. KJEF should be most heavily impacted, followed by KSUS.
Any fog should dissipate by ~1400 UTC.
Gosselin
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion