842
FXUS63 KLSX 260935
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
335 AM CST Wed Nov 26 2025

.KEY MESSAGES...

- Seasonably cold temperatures and dry weather is expected through
  Friday.

- The first snowfall of the season is forecast Friday night into
  Saturday. Probabilities (50-70%) for more significant (3+")
  snowfall are highest across parts of northeast Missouri and
  west-central Illinois.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 334 AM CST Wed Nov 26 2025

Gusty northwest winds are forecast today behind last night`s cold
front. Sustained wind speeds of 20-25 mph with gusts 30-40 mph
are expected. The highest wind speeds/gusts will be across
northeast Missouri and west-central Illinois from mid morning into
early this afternoon. There may be an isolated gust or two near
advisory criteria (45 mph), but winds within the mixed layer
gradually weaken during the day today as the pressure gradient
slowly relaxes. Probabilities for advisory level wind gusts are
below 10% on the latest HREF, but do accelerate quickly as you
head north and east into eastern Iowa and northern Illinois.

Strong low-level cold air advection today will help keep
temperatures in the low to mid 40s. These values would be about 6-8
degrees below normal for the date. Some stratus/stratocumulus may
linger in parts of south-central Illinois until midday, which could
keep highs slightly cooler than forecast.

Increasing mid/high level clouds are expected tonight, with the
thickest cloud cover most likely along/south of I-70. These clouds
along with northwest winds staying up close to 10 mph will help
limit the temperature drop overnight. Lows are forecast to range
from the mid 20s to low 30s from north to south.


Gosselin

&&

.LONG TERM...  (Thursday through Tuesday)
Issued at 334 AM CST Wed Nov 26 2025

(Thanksgiving - Friday)

Seasonably cold and dry conditions will continue through the end of
the work week as a strong (~95th percentile) surface ridge of high
pressure moves across the mid-Mississippi Valley. Highs in the mid
30s to mid 40s are expected each day, with lows Friday morning in
the mid 10s to low 20s.


(Friday Night - Saturday Night)

Spread in model guidance for our first winter storm of the season
has really decreased over the past 24 hours. The GFS/GEFS has
trended strongly toward a more amplified midlevel shortwave trough
moving across the south-central Plains into the Mississippi Valley
on Saturday. This piece of energy though is still about 600-700
miles from the Pacific northwest coast. The North American upper air
network should get a partial sample Thursday evening, followed by a
full sample Friday morning. Therefore, there still could be at least
some subtle changes with the timing/track/strength of this feature
over the next couple of days. Meanwhile, the ECMWF/EPS has trended
colder in the low levels of the atmosphere and now is a lot closer
to the GFS/GEFS. Given the retreating cold/dry air mass, wetbulbing
should play a very important role. Model soundings show very dry air
below 10 kft AGL Friday evening, with max dewpoint depressions
around 25C.

Strong moisture convergence is expected Friday night on the nose of
a 40-50 kt (>95th percentile) southwesterly low-level jet. This
strong forcing will quickly saturate the lower troposphere after a
period of sublimation cooling. This means it is likely that the
dominant precipitation type at onset should be snow areawide, as
temperatures cool to their wetbulb values. The question then becomes
how long does it stay snow? For parts of central/southeast Missouri,
this shouldn`t be too long as enough of the boundary layer warms
sufficiently above the freezing mark. However, snow should hang on
longer the further north and east you travel. Snow very well may
continue through the entire morning and into the early afternoon
across parts of northeast Missouri and west-central Illinois. These
locations may not change over to rain until the low-level cyclone
moves toward the Missouri-Iowa border. Another factor that is
expected to help delay the changeover is dynamic cooling. There is
an increasing signal for high precipitation rates (>=0.25" liquid
equivalent in 6 hours) on the LREF. Probabilities are in the 40-60+%
range late Friday night into Saturday morning. Anecdotally, past
events have shown that it is usually very difficult for moderate-
heavy snowfall to turn over to rain UNTIL forcing for ascent abates
and precipitation rates decrease.

Confidence in impactful snowfall accumulations is rising given the
decreasing model spread and a stronger signal for high precipitation
rates. Amounts should increase the further north and east you
travel. This puts our west-central Illinois counties being the most
favored area for the heaviest snowfall totals. LREF probabilities
for 3+" of snow by Saturday evening range from 30-70% in northeast
and east-central Missouri into Illinois. For reference, those values
are about 15-30% higher than the 1200 UTC cycle yesterday. There
also is an increasing signal for heavy snowfall (5+") in/around west-
central Illinois. This is where the LREF has probabilities of 30-
50%, and where the Extreme Forecast Index (EFI) from the EPS
approaches 0.8 with a Shift of Tails (SOT) near 5. This illustrates
fairly high confidence (at least within the EPS suite) of heavy
snowfall in this area of the CWA. It is possible a winter storm
watch may be needed in/around west-central Illinois if this signal
remains over the next 24 hours.


(Sunday - Tuesday)

Model spread has also decreased for late this weekend into early
next week. Ensemble guidance generally shows less mid/upper level
troughing in the desert southwest early next week and strong
confluence across the Upper Midwest/Great Lakes. This means that any
midlevel shortwave moving toward the mid-Mississippi Valley is
likely to get sheared out/weaken. The most likely scenario for this
period is unseasonably cold and largely dry conditions. The air mass
coming into the area looks to be truly arctic in origin, with cross-
polar flow aloft evident on both the GEFS/EPS mean 500-hPa height
fields. Forecast highs are in the 20s/30s each day, with lows in the
teens. These values would be on average about 10-20 degrees below
normal. There also could be impact from snow cover in northern
sections of the area, but of course this is far from certain.
However, if parts of the area do see several inches of snow, the
ground may stay covered into early next week. If there is any snow
on the ground, lows in the single digits would be likely.

In terms of precipitation chances, there may be some light
precipitation during this time period. Given the arctic air mass
expected to be in place, if any precipitation does fall, it is very
likely to be all snow. There still is a signal for light snow
sometime early next week. LREF probabilities over a 24-hour period
peak out in the 50-65% range ending Tuesday morning for measurable
snowfall, but fall to 20-30% for at least 1".


Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1052 PM CST Tue Nov 25 2025

An area of low VFR stratus is pivoting east-southeastward mainly
north of the region, impacting KUIN. As temperatures cool further
tonight, this stratus is expected to drop into MVFR territory
through the morning, improving mid morning as temperatures warm.
Otherwise, VFR flight conditions are expected through the rest of
the period at KUIN and through the whole period at the other local
terminals, with northwesterly winds weakening around sunset.

Elmore

&&

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

$$

WFO LSX