O'Fallon, Missouri 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

221
FXUS63 KLSX 230002
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
602 PM CST Sun Feb 22 2026

.KEY MESSAGES...

- Dry weather with below normal temperatures will persist through
  Tuesday morning. Temperatures will warm back above normal for
  Tuesday through the end of the week.

- The next chance for rain for the area will be on Wednesday night
  and Thursday morning. There may also be some rumbles of thunder
  late Wednesday night across parts of southeast Missouri.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 250 PM CST Sun Feb 22 2026

A strong, cold high pressure ridge over the Great Plains will
build east into the Mississippi Valley over the next 24 hours. The
tight pressure gradient between the ridge over the Plains and
deepening low pressure off the Mid-Atlantic Coast is producing
strong and gusty northwest winds across Missouri and Illinois this
afternoon. Winds will diminish slowly tonight into Monday morning
as the ridge builds east, although the strengthening low off the
East Coast will maintain a relatively tight pressure gradient
through much of Monday. Temperatures are already around 10 degrees
colder than 24 hours ago, and with continuing cold advection lows
tonight are expected to be around 15 degrees below normal in the
low to mid teens in most locations. 10-15 mph sustained winds on
Monday morning combined with these low temperatures will produce
wind chill values ranging from around zero to around 5 degrees
below. While this is well above Cold Weather Advisory criteria,
it`s still quite chilly, especially after our recent stretch of
mild weather. Guidance shows weakening winds ending the cold
advection on Monday afternoon. Strong insolation with full
sunshine will lead to a 20-25 degree diurnal warm up with highs
Monday afternoon in the low to mid 30s. Still some concern for
elevated fire danger Monday afternoon, although current
indications are that areas which reach minimum relative humidity
criteria will not coincide with areas that maintain wind criteria
through the afternoon..

Carney

&&

.LONG TERM...  (Monday Night through Next Sunday)
Issued at 250 PM CST Sun Feb 22 2026

Light and variable surface flow on Monday evening turns to the south
by Tuesday morning as the ridge axis moves into the Ohio Valley.
Guidance suggests the sky will be clear to mostly clear Monday
evening, and the light winds should produce good radiational cooling
conditions.  Expect temperatures to dip into the upper teens to low
20s Monday evening, before steading down and then rising slightly
before sunrise Tuesday morning after the wind shifts to the south.
Southwest flow increases during the day on Tuesday as a short wave
and its attendant surface low moves across the Upper Midwest into
the Great Lakes.  Deterministic temperature guidance shows highs
ranging from the mid 40s to near 60 from east to west across the
forecast area.  The LREF and NBM high temperature IQRs on Tuesday
are fairly tight at only 3-4 degrees which lends a good deal of
confidence to the high temperature forecast.  Tuesday will likely be
the week`s best chance for elevated fire danger due to the warming
temperatures, relatively low (although increasing) dew point
temperatures and strengthening southwest flow.  However, conditions
continue to look marginal unless afternoon mixing produces lower dew
point temperatures than currently forecast...which is entirely
possible.

The cold front associated with the aforementioned short wave moves
south of the forecast area into far southern Missouri or northern
Arkansas by early Wednesday morning where it stalls.  Variability in
the position of the boundary is evident in the ensembles as
temperature IQRs increase to 6-8 degrees Wednesday ahead of the next
upstream short wave.  This system moves from the Plains into the Mid
Mississippi Valley late Wednesday night into Thursday.  It forces a
surface low to develop on the stalled boundary which moves across
Missouri and Illinois Thursday morning.  Guidance shows moderate to
strong low level moisture convergence ahead of the low which
produces precip Wednesday night into early Thursday morning.
Temperatures look warm enough that most if not all of this precip
should be liquid.  There may be a bit of rain/snow mix in the cold
sector as precip ends from northwest to southeast on Thursday. but
surface temperatures are not expected to fall below freezing
Thursday so no snow accumulation is expected.

The remainder of the forecast looks relatively uneventful as the
flow aloft becomes zonal.  There are some differences in medium
range guidance with respect to the long wave pattern.  The EC keeps
the northern stream jet farther south across the the northern US
while while the GFS keeps it a bit farther north across southern
Canada.  The EC therefore allows colder air to remain over the
Midwest through the period while the GFS is warmer.  The differences
in the position of the jet stream manifest in the LREF as wide
temperature IQRs (as large as 15-20 degrees) on Saturday and Sunday.
The EC members of the LREF are also wetter at the end of the
forecast on Sunday as the more southern track of the jet stream
allows a short wave to dip into the Midwest which produces a chance
for precip across the area.  With these differences evident in the
guidance, confidence in the forecast is relatively low for next
weekend.


Carney

&&

.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 600 PM CST Sun Feb 22 2026

VFR conditions are expected throughout the 00Z TAF. Gusty
northwest winds will persist through the night, and weaken late in
the period tomorrow. Some patchy MVFR stratus may reach near St.
Louis terminals overnight, but is not expected to reduce
categories. Will monitor the eastward progression of this stratus
and amend as needed.

BRC

&&

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

$$

WFO LSX