Area Forecast Discussion

255
FXUS63 KLSX 251740
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1140 AM CST Tue Nov 25 2025

.KEY MESSAGES...

- Behind a cold front later today, dry weather and below normal
  temperatures are forecast Wednesday through Friday.

- Widespread precipitation is expected Friday night - Saturday.
  Chances for the first accumulating snowfall of the season are
  increasing, particularly for parts of northeast Missouri and
  west- central Illinois.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 323 AM CST Tue Nov 25 2025

Widespread light rain continues to move eastward across southwest
and south-central Illinois early this morning. This rain should
exit the area over the next few hours as low-level moisture
convergence heads toward the lower Ohio Valley. Further west, fog
and low stratus is the main story. Lowest visibilities in fog
early this morning are forecast to be across central/northeast
Missouri and west-central Illinois. Some patchy dense fog is
expected in this region. If confidence increases in more
widespread dense fog, an advisory would likely need to be added
and we will continue to monitor conditions over the next few
hours.

A surface low is forecast to move across the Upper Midwest later
today, with an attendant cold front draped to its south. This front
will sweep from west to east across the area late this
afternoon/evening. Surface convergence along the boundary and
increasing mid/upper level forcing for ascent ahead of the trough
should lead to isolated - scattered light rain shower activity near
the front. Behind the front, winds turn out of the northwest and
become gusty. Winds at the top of the mixed layer overnight tonight
exceed 40 knots. The timing of the front suggests we will not be
able to mix gusts quite high enough to trigger a wind advisory (45+
mph), but gusts of 30-40 mph are likely. The HREF also supports
gusts staying sub advisory level, with only a 20-30% chance of
seeing 45+ gusts across northeast Missouri and west-central
Illinois.

Temperatures today will be on the mild side, though mainly due to
the anomalously warm start to the day. It is currently in the upper
40s to mid 50s across much of the area. These readings are close to
or slightly above normal daytime highs already. The fog and low
stratus however really should limit diurnal warming. Temperatures
are only expected to climb about 5-7 degrees into the afternoon as
highs top out in the mid 50s to near the 60 degree mark.


Gosselin

&&

.LONG TERM...  (Wednesday through Monday)
Issued at 323 AM CST Tue Nov 25 2025

(Wednesday - Friday)

Much colder (and drier) air will continue to advect into the mid-
Mississippi Valley on Wednesday behind tonight`s cold front. This
seasonably cold air mass will remain then in place through the
remainder of the work week. High temperatures are expected to be in
the mid 30s to mid 40s from north to south, with lows in the mid 10s
to upper 20s. On average, these temperatures will be about 10
degrees below normal for late November.


(Friday Night - Saturday Night)

Model differences remain high still for the next storm system, which
will impact the area Friday night through Saturday evening. The same
differences denoted yesterday remain with how the ECMWF/EPS handles
the midlevel trough moving out of the central Plains compared to the
GFS/GEFS. The GFS/GEFS is weaker/flatter than the more amplified
ECMWF/EPS. This piece of energy is currently in the middle of the
Pacific Ocean, well south of the Aleutian islands of Alaska. This
midlevel shortwave trough is expected to be partially sampled by the
North American upper air network Thursday evening, and fully sampled
Friday morning. Unfortunately, that is not much time before the
first impacts may be seen in our region.

The situation continues to be a "thread the needle" type of setup
for accumulating snow. Surface temperatures are marginal, with a
requirement for wetbulbing aided by very dry air in the lowest few km
of the troposphere to yield snow. At this time, snow is more likely
to last longest the further north you head. Probabilities of at
least 1" of snow on the LREF range from 30-70%, and 20-50% for 3+".
There is also still a low threat for very significant (6+")
snowfall. The LREF shows 10-30% of at least 6", mainly in northeast
Missouri and west-central Illinois. The vast majority of those are
EPS members, which have the more amplified system but also far
enough south to keep those sections of the area all snow. The best
chances of travel impacts will of course be where the heaviest snow
falls, and it likely will require at least a couple of inches to
cause problems on area roadways. Ground/road temperatures will be
quite warm, which necessitates at least some temporal persistence of
moderate snowfall rates. Otherwise, any accumulations would either
not occur, or stay confined to grassy/elevated surfaces.

The rain/snow line is expected to at least slightly move north
during the day on Saturday as surface temperatures warm at least a
few degrees. How far north the rain gets is of course uncertain this
far out. The more amplified ECMWF/EPS would turn nearly the entire
area over to a cold rain while snow would remain the primary
precipitation type at least in northern sections of the area on the
GFS/GEFS. All in all, there is still plenty to sort out and an
overall low confidence forecast.


(Sunday - Monday)

Forecast uncertainty increases even further to end the weekend
heading into early next week. Model guidance is really struggling
with how to handle the anomalous troughing in the desert southwest
and the strength of an incoming arctic air mass from southern
Canada. The WPC clusters of the 500-hPa height pattern show two
distinct scenarios. One has a deeper southwest trough, with pieces
of energy ejecting out and interacting with a strong southwest-
northeast baroclinic zone. This scenario would yield multiple
additional rounds of precipitation in our area, with all types
(snow/sleet/freezing rain/rain) on the table. The second scenario
shows a weaker southwest trough with a strong arctic air mass
penetrating much further south and east. This scenario would likely
yield dry weather (or perhaps some very light snow) and much below
normal temperatures. At this time, the two scenarios are almost
split 50/50 on the grand ensemble. Most EPS members favor the
colder, drier scenario whereas the GEFS favors the more active
scenario with multiple additional waves of wintry weather. Looking
at hemispheric charts, the incoming air mass does look truly arctic
in origin, with cross-polar flow depicted at mid/upper levels of the
atmosphere. This pattern may give more credence to the colder, drier
EPS, but things can certainly change in the coming days so stay
tuned.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1139 AM CST Tue Nov 25 2025

Low clouds have remained lock in over the region with bases
generally ranging 500-1000 feet early this afternoon. A cold front
will approach from the northwest this evening, arriving at central
MO and KUIN between 22z-00z and metro terminals 01z-03z. Much
drier air will help erode the low level moisture with bases
gradually lifting to MVFR this afternoon/evening and VFR tonight.

Once the front passes, winds will be become quite strong with
west-northwesterly gusts near 25 knots becoming common overnight.
The strongest winds cross the region early Wednesday morning with
gusts exceeding 30 knots at times. The best wind potential will
be around KUIN with a few gusts reaching 35 knots a times. Winds
slowly subside through the day Wednesday with VFR persisting
through the end of the period.

Maples

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion