691
FXUS63 KLSX 091945
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
145 PM CST Tue Dec 9 2025

.KEY MESSAGES...

- Very windy conditions are expected behind a cold front late tonight
  through Wednesday morning. Sustained northwest winds of 20- 30
  mph with gusts of 35-50 mph are forecast.

- Gradually colder and colder temperatures are expected through
  the weekend, with the coldest period expected Saturday
  night/Sunday.


&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 145 PM CST Tue Dec 9 2025

A clipper is currently across southeast North Dakota and will
progress quickly into the Great Lakes overnight tonight. A cold
front draped to its southwest will progress eastward across the
mid- Mississippi Valley late tonight/early Wednesday morning.
Behind the front, winds will swing to the northwest and increase
in speed. Sustained wind speeds of 20-30 mph with gusts in the
35-50 mph range are expected. The highest winds/gusts should be
between 0900 and 1800 UTC across eastern Missouri over into
Illinois. The 12Z HREF shows 50-70% probabilities for 45+ mph wind
gusts (advisory criteria) in this time period, and given the
tight pressure gradient and near 50 knots of flow at the top of
the mixed layer, went ahead and issued a wind advisory for much of
eastern Missouri and our Illinois counties. The pressure gradient
relaxes fairly quickly from northwest to southeast during the
morning hours on Wednesday, so while it still will be a bit breezy
during the afternoon, gusts should drop well below the 45 mph
advisory threshold.

Strong low-level cold air advection will also lead to colder
temperatures on Wednesday compared to today. Temperatures should
cool for most locations through much of the morning hours, before
leveling off for the most part in the afternoon. Readings in the 30s
to low 40s are expected from late morning through the afternoon.
Given the strong northwesterly winds, it will feel quite a bit
colder than that though.


Gosselin

&&

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 145 PM CST Tue Dec 9 2025

(Wednesday Night - Friday Night)

Seasonably cold temperatures and dry weather is forecast Wednesday
night and Thursday as a surface ridge of high pressure progresses
across the Mississippi Valley.

Yet another clipper is expected to move from northwest to southeast
Thursday night into early Friday. This system will be further
south/southwest, with the track of the low potentially across
northern sections of the area. There remains some uncertainty with
the track of this system, but most ensembles from the LREF argue for
little/no impacts from this clipper in our area like its
predecessors this December. Climatology also strongly argues for
impacts (i.e., accumulating snow) to stay to our northeast more
across north-central Illinois into Indiana.

Temperatures will be closely tied to the track/timing of this
clipper, but warmer (upper 20s - mid 30s) lows are expected Thursday
night ahead of this system, with colder temperatures building back
southward behind it. By Friday night, lows in the teens/twenties are
expected.


(Saturday - Sunday Night)

Confidence is increasing in a short, but intense period of anomalous
cold for this upcoming weekend. The coldest 24-36 hour period is
expected between Saturday night and Sunday night. This is when lows
in the single digits/teens are forecast, with highs Sunday only in
the teens/twenties. These readings would be about 15-25 degrees
below normal for mid December. There is still some uncertainty on
exactly HOW cold, as our CWA will be more toward the southwestern
edge of the most extreme portion of this air mass. The spread on the
inter-quartile range for temperatures from the NBM this weekend is
still almost 10 degrees. The deterministic forecast mentioned
detailed above though generally sits near the 75th percentile, and I
would not be surprised to see both Saturday night`s lows and
Sunday`s highs trend at least toward the 50th percentile of the NBM.
This would be potentially knock those values down about 3-5 degrees.
If this occurs, we may be looking at our first extreme cold/wind
chill products of the season. Probabilities on the LREF for wind
chills at or below -10F are in the 30-60% range along/north of I-70
and 10-40% for -15F or colder.

Dry weather is favored this weekend. The only chance of snow looks
to come Saturday/Saturday night behind the main push of arctic air.
Deterministic model guidance depicts some low/mid level
frontogenesis combined with a midlevel shortwave trough moving
across the Upper Mississippi Valley. Like a broken record, this axis
of snow is very likely to setup northeast of our region. The highest
probabilities for measurable snow stretch from central Iowa
east/southeast across north-central Illinois into Indiana.
Probabilities drop further southwest, with only a 20-40% chance for
any measurable snow in northeast Missouri and west-central Illinois
at this time.


(Monday - Next Tuesday)

Ensemble guidance is in very good agreement that a quick moderation
in temperatures will occur early next week. Mid/upper level heights
rise with strong low-level warm air advection commencing in the wake
of the departing surface high. Temperatures are forecast to warm
back closer to seasonal normals by Tuesday along with dry weather
also being favored.


Gosselin

&&

.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...Wind Advisory from 3 AM to noon CST Wednesday 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 from 3 AM to noon CST Wednesday 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