St. Charles, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

303
FXUS63 KLSX 192333
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
533 PM CST Fri Dec 19 2025

.KEY MESSAGES...

- After daily temperatures fluctuate through the weekend,
  unseasonably and potentially record-breaking warmth is forecast
  next week.


&&

.SHORT TERM...  (Through Late Saturday Night)
Issued at 202 PM CST Fri Dec 19 2025

Current water vapor imagery shows yesterday`s potent upper-level
trough quickly moving eastward away from the Middle Mississippi
Valley. As a result, northwesterly flow over the region is weakening
as the axis of a surface ridge moves across the CWA. This has skies
mostly clear but air temperatures cool, running at or just below
seasonal normals.

The surface ridge will continue to drift eastward through the
evening into tonight, causing winds across the CWA to become
southerly as it does so. This wind direction and magnitude along
with passing high clouds will keep temperatures from dropping below
freezing for most locations.

This will set the stage for a warmer start to the day Saturday, with
winds gradually becoming southwesterly ahead of an approaching cold
front driven by a low-amplitude trough moving across the Upper
Midwest. This will enhance the warm air advection in place, pushing
afternoon temperatures into the mid 50s for most locations south of
I-70. North of that corridor, frontal timing will hinder the diurnal
temperature curve and keep temperatures at or just below 50 degrees.
Low-level moisture will not have recovered after yesterday`s FROPA,
combining with a lack of upper-level forcing to mitigate rainfall
chances. The lack of deeper northwesterly post-frontal flow will
keep temperatures from free-falling overnight, with lows for most
locations falling to right at or just below freezing behind the
front.

Elmore

&&

.LONG TERM...  (Sunday through Next Friday)
Issued at 202 PM CST Fri Dec 19 2025

For Sunday morning, the axis of the upper-level trough will be just
east of the CWA, with northwesterly flow weakening through the day
per guidance consensus. With the core of the post-frontal air mass
from Saturday`s FROPA passing northeast of the CWA, temperatures
through the day are expected to vary by approximately 10 degrees
from northeast to southwest, through remain around climatological
normals.

This cool down will be brief, as a majority of guidance shows upper-
level ridging quickly building into the central CONUS early next
week. Beneath this ridge, an anomalously warm air mass will move
into the Midwest. As a result, temperatures will rapidly rise above
seasonal normals early next week, peaking on Thursday (Christmas
Day) as low- to mid-level temperatures reach their warmest point
during the period. Then, global ensemble means show these
temperatures topping out 15-17 degrees C, climatologically favoring
surface temperatures in the low 70s. Nearly every global ensemble
member shows surface winds out of the southwest, giving temperatures
a boost across portions of Missouri along and south of I-70 thanks
to adiabatic warming due to downslope flow off the Ozarks. This
solution would help raise temperatures to as warm as the mid-70s
during the afternoon. At this lead time, there is of course
uncertainty in finer details like the exact wind direction and upper-
level cloud cover, but narrow ensemble spread leads to high
confidence that high temperatures will at least approach record
highs. See the climate section below for additional details.

There is a low chance (10% or less) for a FROPA on Thursday, but a
majority of guidance shows this occurring on Friday or Saturday as
the ridge weakens. A lack of deep northwesterly flow shows that this
front will lack much bite, leading to relatively minor impacts on
temperatures. Ensembles showing them decreasing, but remaining above
normal on Friday and Saturday. How much above normal is uncertain,
however, due to guidance differences in the amplitude of the trough,
as the spread within the IQR of global ensembles for temperatures
increases to around 15 degrees.

Lastly, rain chances remain low through the period. A low-level jet
immediately south of the region across the Mid South will force
light rainfall across the same region, potentially (20% chance)
skimming portions of southeastern Missouri and southwestern Illinois
at times late Monday through Tuesday. The variability in the timing
of the front late in the week or early next weekend as well, as the
degree of moisture return ahead of it, leads to low confidence in
additional rainfall amounts. However, the majority of
global ensemble members keep the CWA dry through Friday.

Elmore

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 532 PM CST Fri Dec 19 2025

Dry and VFR flight conditions will prevail through the TAF period
with the only noteworthy items being 1.) marginal LLWS overnight
into Saturday morning as a 50-kt southwesterly low-level jet
overlays light southerly surface winds, and then 2.) a dry cold
frontal passage around midday Saturday veering winds toward the
northwest with a few gusts nearing 20 kt.

Pfahler

&&

.CLIMATE...
Issued at 200 AM CST Thu Dec 19 2025

Well above normal temperatures are forecast around Christmas,
with record temperatures within reach. Records for our three
climate sites and the years that they occurred are listed below.

   KSTL  KCOU  KUIN
12/2473(2021)74(2021)69(2021)
12/2571(1889)74(1889)66(2019)


&&

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

$$

WFO LSX