523
FXUS63 KLSX 101050
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
450 AM CST Wed Dec 10 2025

.KEY MESSAGES...

- Today will be much colder than yesterday with temperatures
  falling through the day. Very gusty winds will make it feel
  even cooler.

- Potentially dangerous cold is forecast this weekend. Forecast lows
  Saturday night are forecast to fall to around 0 in northeast
  Missouri and west-central Illinois with wind chills solidly in
  the negatives.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 154 AM CST Wed Dec 10 2025

A deep surface low pressure system passing through the Upper Midwest
is dragging a cold front through the Mid-Mississippi Valley this
morning. Ahead of the cold front, light rain has wet the ground in
portions of northeast Missouri. More impactful, though, the
system`s tight pressure gradient has resulted in widespread gusty
winds with a 33 kt gust observed as early as 05z. Gusts will only
become stronger as the cold front passes, with gusts of up to 50
mph expected through early morning. For this reason, a Wind
Advisory remains in effect from 3am until noon today, with the
strongest wind gusts forecast between 12 - 15z when daytime mixing
begins. Winds will begin to diminish in the afternoon.

Strong cold air advection will follow the front, and it will become
apparent quickly. Daily highs for most likely occurred near midnight
with temperatures falling into the low 30s and 40s by this
afternoon. This is 10 - 20 degrees cooler than yesterday`s afternoon
highs, and the concurrent elevated winds will make it feel much
cooler.

Jaja

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 154 AM CST Wed Dec 10 2025

The chance of snow returns to portions of northeast Missouri
southeastward into south-central Illinois late Thursday through
Friday morning. The track of the system continues to trend south,
with the primary corridor of snow forecast to pass through central
Illinois. Because of this LREF probabilities of measurable snow are
increasing, with up to a 75% chance of 0.1" over 24 hours along our
northern border. These probabilities decrease drastically when
increasing the amount, however. The LREF probability of 1" over 24
hours drops to 20 - 30%. Even these low values should be taken with
a grain of salt given the LREF uses a 10:1 ratio and borderline
freezing temperatures would cause SLRs to be lower. In short,
impactful snow is not anticipated.

An Arctic airmass will filter in behind the Friday system,
plummeting temperatures to the coolest we`ve seen this season. The
cold snap is forecast to last from Friday night through Monday
morning with the coldest period being Saturday night through Sunday
night. Currently, our forecast has single digits to teens for lows
Saturday night - Monday morning with highs Sunday only reaching the
teens to twenties. There is still uncertainty regarding exactly how
cold temperatures become despite the NBM cooling down from its
warmer forecast yesterday. Its interquartile temperature spread for
Saturday night, Sunday, and Sunday night are all >10 degrees, and
it`s still at the 75th percentile for highs on Sunday and above the
50th percentile for lows Sunday night as of the 12/9 19z run. Even
with the suspiciously high temperatures, wind chills Saturday
night/Sunday morning come very close to Cold Weather Advisory
criteria both in our northernmost counties where criteria is <=-15F
and in portions of south-central Illinois where criteria is <=-10F.
LREF probabilities of reaching criteria have increased to 70 - 80%
for wind chills <-15F and to 80 - 90% for wind chills <-10F. With
high certainty that the current forecast temperatures will continue
to cool and considering increasing ensemble probabilities,
confidence is definitely increasing in a Cold Weather Advisory being
needed this weekend.

The chance for snow returns on Saturday with another system that`s
forecast to track to our northeast, but has trended much further
southwest in the past 12 hours. This places us in a similar
situation to that of this coming Thursday - just southwest of the
snow, but just close enough for the Quincy, IL - Effingham, IL
corridor to be glanced by light snow. Because of the southern shift
(and probably a washed out snow gradient), LREF probabilities of
measurable snow have increased dramatically from under 50% to now
over 70%. With the cold airmass squarely in place by that time, any
snow that does fall will stick. There is still time for the system
to wobble around the Midwest, so snow is not promised as much as it
is becoming possible.

Jaja

&&

.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 444 AM CST Wed Dec 10 2025

A cold front is passing through the bi-state this morning,
shifting very gusty winds to northwesterly behind it. A Wind
Advisory is in effect until noon today for most of the forecast
area. Sustained winds of up to 25 kts and gusts of up to 45 kts
are expected until then. Winds will slowly diminish this
afternoon but will still remain elevated before becoming light
tonight.

Solidly MVFR ceilings are also following the cold front. These
will continue to creep south through the day, and are expected to
persist until late tonight/early tomorrow morning before clearing.
All upstream observations as of 11z show 2000 - 3000 ft ceilings,
but an isolated 1500 - 2000 ft ceiling may appear every now and
again.

Jaja

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory until noon CST today for Franklin MO-Jefferson MO-
     Knox MO-Lewis MO-Lincoln MO-Marion MO-Monroe MO-Pike MO-
     Ralls MO-Saint Charles MO-Saint Louis City MO-Saint Louis
     MO-Shelby MO-Warren MO.

IL...Wind Advisory until noon CST today for Adams IL-Bond IL-Brown IL-
     Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-
     Macoupin IL-Madison IL-Monroe IL-Montgomery IL-Pike IL-
     Saint Clair IL.

&&

$$

WFO LSX