Area Forecast Discussion

262
FXUS63 KLSX 091716
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1116 AM CST Tue Dec 9 2025

.KEY MESSAGES...

- Today will be the warmest day of the week with highs in the 40s
  & 50s. Temperatures then plummet behind multiple cold fronts
  with highs in the teens forecast for some on Saturday.

- Wednesday will be blustery with wind gusts of 30 - 40 mph and wind
  chills up to 10 degrees below the air temperature.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 300 AM CST Tue Dec 9 2025

Warm air advection has begun in the region and will only become
stronger today as the surface pressure gradient tightens ahead of
our next cold front. This influx of warmth in addition to insulating
cloud cover has caused temperatures to climb this morning, which
will serve as a nice launching pad for the seasonably mild
temperatures this afternoon. Increasingly strong warm air advection
along southwest flow is expected to rocket temperatures into the 50s
for areas without snow and that see the most sun, namely
southeast/central/east-central Missouri. East-central Missouri will
get an additional boost in highs from downsloping off the Ozarks.

The warmth will be short-lived. The aforementioned cold front will
pass through the area overnight Tuesday, bringing with it strong
northwest winds and much cooler air. The strongest wind gusts are
expected to occur Wednesday morning as the ~50 kt winds topping the
boundary layer begin to mix down. This will result in a brief period
of 40 - 45 mph gusts in our far northern counties, on the cusp of
Wind Advisory criteria. Elsewhere, the day will still be windy with
sustained winds upwards of 25 mph and gusts of 30 - 40 mph. Strong
low-level winds will result in strong cold air advection as well,
with temperatures remaining steady or falling through the day. Aside
from far southwest Illinois and southeast Missouri which will see
ample sunshine and less cold air advection, highs on Wednesday will
be about 10 degrees cooler than Tuesday.

Jaja

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 300 AM CST Tue Dec 9 2025

Our next chance for precipitation will come Thursday into Friday and
will only exist along our northeastern CWA border (think Quincy, IL -
 Salem, IL give or take). Although LREF probabilities show a high
likelihood of measurable precipitation falling in these areas
during this period (60 - 70%), amounts are confidently slim.
Probabilities of less than 0.05" of precipitation falling are also
60 - 70%. Obviously the interpretation of this changes based on
precipitation type, which is uncertain. The freezing line is
expected to be in the vicinity of our northern border, with
ensembles trending warmer at least in the past 24 hours. If these
locations do see precipitation, it may start off as light rain
with only a flake or two present overnight. Then again, if
temperatures are cooler than forecast, they may see light snow on
the order of a trace.

More impactful will be the cold this weekend, that`s coming in a
little later than previously forecast. The cold will still begin
Friday night, but it is now centered around Sunday instead of
Saturday and ends Monday. There is still uncertainty regarding how
cold it will get as this is tied to how far south in the CONUS the
Arctic airmass spills. The heart of the airmass has been trending
away from our region, and the NBM has warmed in response. However,
given the anomalous 10th climatological percentile cold, the pre-
existing snowpack, and a 90th climatological percentile incoming
surface high, I suspect the NBM has warmed a little too much. The
latest 01z 12/9 NBM run has cooled a bit, but its forecasts on
Sunday, when we`ll be closest to the surface high, are still above
the 50th percentile. This trend is expected to continue as the
NBM continues to catch on over the next few days. In the case of
any nighttime radiational cooling, however, it`ll very likely
still be too warm.

Jaja

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1111 AM CST Tue Dec 9 2025

South/southwest winds will veer more to the west ahead of an
approaching cold front. Behind the front, winds swing to the
northwest and increase in speed/gusts. Highest gusts of near 40
knots are forecast Wednesday morning at KUIN and the metro
terminals. There may be a period of MVFR stratus at well impacting
KUIN, but chances are higher further to the north/northeast so
left mention out for now.

Gosselin

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion