432
FXUS63 KLSX 082009
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
209 PM CST Mon Dec 8 2025

.KEY MESSAGES...

- Up and down temperatures are expected this week with highs in
  the 40s/50s Tuesday transitioning to potentially dangerous cold
  this weekend.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 208 PM CST Mon Dec 8 2025


A surface ridge of high pressure will continue to slide
southeastward into the lower Mississippi/Appalachian Mountains
overnight tonight. Winds will turn out of the south/southeast in
its wake, with speeds gradually increasing overnight as the
pressure gradient tightens. This increase in winds along with some
mid/high level clouds streaming in from the northwest should
actually yield some rising temperatures overnight. Lows in the mid
20s to near 30 degrees are forecast from northeast to southwest,
but these lows likely will be reached in many areas around/before
the midnight hour.

Winds are expected to veer more to the southwest on Tuesday ahead of
an approaching cold front. At least partial sunshine and low-level
warm air advection are expected to yield the warmest day for most
locations in over 2 weeks. Highs in the mid 40s to mid 50s are
expected across the bi-state area. Coldest locations are forecast to
be across northeast Missouri and west-central Illinois. This is
where there is still a snow pack on the ground. Warmest locations
are expected to be across portions of central/east central Missouri.
south of the snow pack and in a region that will see winds favorable
for downslope off of the Ozark Plateau.


Gosselin

&&

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 208 PM CST Mon Dec 8 2025

(Tuesday Night - Thursday Night)

Topsy-turvy temperatures are expected for midweek as multiple cold
fronts pass through the region. The first is expected to come late
Tuesday night. Temperatures ahead of this boundary will be quite
mild, with lows only dropping back into the low to mid 40s. The
exceptions are in northwest sections of the area, where lows in the
low to mid 30s are forecast due to the timing of the frontal
passage. Any threat for precipitation should stay to our northeast.
Like most clippers, a vast majority falls as snow along/northeast of
the track of the surface low. This low is forecast to track close to
the climatologically favored zone across the Upper Midwest/Great
Lakes.

Strong low-level cold air advection is forecast on Wednesday. Not
surprisingly, steady or slowly falling temperatures are expected
during the day. For most areas, readings will be in the mid 30s to
low 40s from north to south during the afternoon. In addition to the
cooler temperatures, it certainly looks windy. Sustained northwest
winds of 15-25 mph are forecast with gusts of 30-40 mph. The
strongest gusts are likely to be Wednesday morning as diurnal mixing
commences. A brief 1-2 hour period of near-advisory gusts (45+ mph)
are possible 12-15Z in far northern areas as winds atop the mixed
layer approach 50 knots.

Seasonably cold conditions are forecast Wednesday night through
Thursday night along with mostly dry weather. We will have to keep a
loose eye on the Thursday/Thursday night time period for the
potential for some precipitation. Model guidance suggests some
increasing low-level moisture convergence across a tight northwest-
southeast baroclinic zone across the region during this time period.
Chances for measurable precipitation range from 20-60% on the LREF
from southwest to northeast, but drop quickly into the 10-25% range
for at least 0.10" of liquid equivalent. Precipitation type isn`t
guaranteed to be snow either, with marginal or too warm temperatures
the further southwest you travel.


(Friday - Next Monday)

The focus heading into the weekend continues to be on the incoming
arctic air mass. While confidence in cold coming with below-normal
temperatures is very high, exactly how cold is still a question
mark. Ensemble guidance has backed off quite a bit with the brunt of
the cold, focusing it more across the Great Lakes/Ohio
Valley/northeast. However, these arctic air masses are very
difficult to stop from bleeding south and east with time,
particularly without strong mid/upper level ridging across the
southeast CONUS (which largely looks absent). Both the EPS and GEFS
forecast 850-hPa temperature anomalies of -20 to -25C along the lee
of the Canadian Rockies later this week. This air mass should come
southeast behind any northwest flow disturbance. Once it does, the
abnormally expansive snowpack to our north will help prevent too
much in the way of modification as it heads southeast. Long story
short, all signs point to a (short) period of anomalous cold
centered on this weekend. At this time, the coldest period is
expected between Friday night and Sunday, with lows in the single
digits (above zero) each night and highs on Saturday in the
teens/twenties (and Sunday possibly as well). These readings would
be about 15-25 degrees below normal for mid December. The spread is
still high though, with inter-quartile ranges from the NBM of about
10 degrees. Given what was described above and the propensity for
shallow arctic air masses to sag southward, I would not be surprised
to see forecast lows/highs trend a bit colder over the next day or
two, and closer at least to the 50th percentile of the NBM.

Dry weather is forecast through the weekend. Anything that does fall
behind the arctic front would fall as snow, but we are not seeing
any signs at this point for measurable snowfall. Probabilities on
the LREF over any 24-hour period don`t really top 25%. The "best"
chance likely would be with some low/mid level frontogenesis behind
the arctic front itself sometime between Friday night and Saturday
night, but at this point in time there is no consensus on if this
will happen at all, and if so, where.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1118 AM CST Mon Dec 8 2025

Some stratus remains across northeast Missouri and west-central
Illinois late this morning. This should advect out of KUIN over
the next couple of hours. Thereafter, dry/VFR conditions are
expected areawide. Light/variable winds are forecast the res of
the afternoon. After the passage of a surface ridge of high
pressure, look for winds to turn out of the southeast overnight.
Winds are then forecast to gradually veer more to the southwest
Tuesday morning with speeds around 10 knots.

Gosselin

&&

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

$$

WFO LSX