087
FXUS63 KLSX 081720
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1120 AM CST Mon Dec 8 2025

.KEY MESSAGES...

- Roller coaster temperatures are expected this week with highs in the
  50s for some on Tuesday transitioning to potentially dangerous
  cold this weekend.

- The chance of snow Thursday into Friday has decreased to 10 - 20%.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 311 AM CST Mon Dec 8 2025

The post-frontal cold airmass that tanked lows this morning will
shift east throughout the day with low-level winds shifting to
southerly in its wake. These southerly winds in tandem with a
tightening pressure gradient will advect much warmer air into the
region through Tuesday night. Though warm air advection will begin
today, it will start too late in the day to be impactful to this
afternoon`s highs. The lingering cold air will play more of a role
in this regard, with temperatures north of I-70 (MO)/I-64 (IL)
remaining at or below 35 degrees. These same areas will see a ~10
degree boost in low temperatures tonight as the warm air finally
takes hold, whereas locations to the south will see another night in
the 20s.

Tuesday`s highs and lows will take massive leaps from days prior.
With high pressure stationed to our south and east and low pressure
pushing in from the northwest, the pressure gradient in the Mid-
Mississippi will be tightening throughout the day. Increasing
southwesterly winds will enhance the ongoing warm air advection,
rocketing highs into the mid-40s to mid-50s. Though this is a high
confidence scenario given the 3-4 degree NBM interquartile spread
across the area, with this level of warm advection, possible
downsloping off the Ozarks, and the NBM`s consistent under-performing
on warm cool season days, I suspect this forecast may be too cool
particularly in southeast MO and southwest IL where confidence is
highest (>80%) in clear skies through the afternoon. Because of
this, I`ve inched highs in these locations up. Lows Tuesday night
will be warmer than today`s highs with the majority of the CWA
only falling into the upper 30s to mid-40s.

Jaja

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 311 AM CST Mon Dec 8 2025

Two cold fronts will pass between Tuesday night and Friday, with the
first cooling the region down to near to below normal and the second
plummeting the region into the dead of winter. The Tuesday night
cold front will cool the region down, but not substantially so. LREF
probabilities of noon temperatures >32 degrees Wednesday are 90 -
100% for most of the CWA, and only as low as 40 - 50% in our far
north closest to the cold airmass. Despite this, wind gusts of up to
25 - 30 mph during the day will make Wednesday feel much cooler than
it actually will be. The colder air will continue to slither south
through the Upper and Mid-Mississippi Valleys with more of it
reaching northern Missouri and west-central Illinois by Thursday.
Although actual temperatures are expected to be 5 - 10 degrees
cooler on Thursday than Wednesday, winds will be lighter to the
point that Thursday may feel similar to if not better than
Wednesday.

Another cold front will push through the CWA Thursday night. This
front will be much more impactful, bringing with it our only chance
of snow this week as well as bitter cold this weekend. Though this
will be our only shot at snow this week, the chance of snow Thursday
night through Friday is low. The track of the system has been
shifting northward and out of our CWA for the past several
forecasts. Current GFS soundings at KUIN during this period suggest
that the best lift will be to our north, leaving very little lift in
the DGZ as far south as KUIN. Moisture will be at a premium as well,
with either the mid-levels or boundary layer being dry at points
between Thursday and Friday. Even if we do manage to squeeze out a
flake or two, confidence is high that snow will be unimpactful given
what will likely be warm ground temperatures, low QPF, and short
duration. The NBM 90th percentile QPF ending Friday evening is about
0.1". Even with a generous SLR of 10:1, this would amount to 1".
Mind you, the probability of measurable snow in our forecast tops
out at 20%. This means that there is a >=80% chance that it will not
snow at all, and - if the 20% chance does come to fruition - a 90%
chance of totals <1".

What`s more significant is the cold following the Thursday night
front. By Saturday, 850 mb temperatures will drop to around -8 to -
14 degrees, within the 10th percentile of climatology. This will be
the coldest airmass of the season thus far, and we will feel it.
Though the current forecast for Friday isn`t extremely cold,
elevated winds will make it feel up to 15 degrees colder in some
locations. The bulk of the cold will settle in Friday night through
Saturday night, with areas north of I-70 likely (50 - 60%) to remain
in the teens for highs. For KUIN, this approaches record low max
temperature territory (12 degrees in 1985). Lows both nights will be
brutal by mid-December standards, falling to near 0 in our far
north. If this forecast holds, portions of northeast Missouri and
west-central Illinois will sink below the 10 degree wind chill mark
by Friday evening and won`t climb above it until Sunday afternoon.
Though we don`t reach Cold Weather Advisory criteria, it is
important to note that this prolonged cold will be dangerous to
individuals without access to heating.

Jaja

&&

.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