Wentzville, Missouri Weather Forecast Discussion

277
FXUS63 KLSX 090817
AFDLSX
Area Forecast Discussion
National Weather Service Saint Louis MO
317 AM CDT Tue Sep 9 2025
.KEY MESSAGES...
- Temperatures will warm with seasonably hot temperatures
  forecast Friday through the weekend along with dry conditions.
&&
.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 316 AM CDT Tue Sep 9 2025
A series of upper/mid-level shortwave troughs/MCVs will pass over
the Mid-Mississippi River Valley today into Wednesday acting to
slowly retract a surface anticyclone that continues to dominate the
area. These features will also produce waves of upper/mid-level
clouds, especially this morning, but weak low-level forcing and dry
low levels limit the prospects of any associated precipitation
reaching the ground in lieu of virga. A dry forecast is further
supported by HREF probabilities of measurable rainfall less than 20
percent, although they some sprinkles cannot entirely be ruled out
this evening and tonight. With retraction of the anticyclone, weak
low-level WAA will ensue today as flow varies between southerly and
westerly going forward. Therefore, high temperatures will warm into
the upper 70s to low 80s F today, mid-80s to around 90 F on
Wednesday with less clouds and warmer 850-hPa temperatures.
Pfahler
&&
.LONG TERM...  (Wednesday Night through Monday)
Issued at 316 AM CDT Tue Sep 9 2025
Model guidance is in agreement that an upper-level ridge will
amplify into the Mid-Mississippi River Valley Thursday into Friday
as the entire flow pattern across the CONUS amplifies and becomes
configured into an Omega Block. This evolution will allow the weak
low-level WAA and southerly flow to persist with 850-hPa
temperatures beginning to climb above the 90th climatological
percentile (around 20 C) by Friday through the weekend with NBM high
temperature ranges relatively tightly clustered around 90 to the mid-
90s F across the CWA, well-above average for mid-September. Low-
level moisture will be slower to increase with a lack of direct Gulf
of Mexico moisture connection in this pattern, keeping heat index
values from rising much above these temperatures but also
deteriorating drought conditions with potential increases in
evaporative demand with dry, hot days.
Sunday into early next week, global model guidance spread increases
as there are mixed signals for a reorganization of the blocking
pattern. A portion of global ensemble membership (approx 44 percent)
has this process transpiring with a potent upper-level trough forced
into the Great Lakes while the larger membership (approx 56 percent)
has ridging of varying amplitude remaining overhead. The former
scenario would allow a weak cold front to reach the region
accompanied by a limited opportunity for precipitation and
subsequent cooler but still above average temperatures next week.
The latter scenario would equate to continued dry conditions and
seasonably hot temperatures. Combining all scenarios, total ensemble
model-derived 24-hour probabilities of measurable rainfall reach 40
to 50 percent around Monday, but probabilities for greater than
0.25" are less than 20 percent. The bottom line is that there is
little, if any, support for any widespread rainfall.
Pfahler
&&
.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1014 PM CDT Mon Sep 8 2025
Dry and VFR conditions will prevail through the TAF period. The
only exception is the potential for river valley fog impacting
portions of southeast and east-central Missouri early this morning.
Incoming high to mid-level cloud cover will stunt any fog
development further west.
Jaja
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&
$$
WFO LSX

NWS LSX Office Area Forecast Discussion