812
FXUS63 KLSX 241723
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1123 AM CST Mon Nov 24 2025

.KEY MESSAGES...

- Widespread rain showers are expected through tonight, mainly
  during the late afternoon/evening hours.

- Dry weather and below normal temperatures are forecast Wednesday
  through Friday.

- Another widespread precipitation event is expected Friday
  night/Saturday, which has the potential to bring the first
  accumulating snow of the season to the area.


&&

.SHORT TERM...  (Through Late Tonight)
Issued at 321 AM CST Mon Nov 24 2025

Areas of dense fog continue early this morning, though recent
surface observations show improvement across western and south-
central Missouri where it is either raining or winds have picked
up. This improvement should spread eastward through the morning.
No changes have been made to the dense fog advisory quite yet, but
we will continue to closely watch trends and are likely to be
able to begin cancelling western portions of the advisory over the
next 1-2 hours.

Isolated to widely scattered light rain showers are possible this
morning, mainly in central/southeast Missouri. The coverage of
showers should increase late this afternoon into the evening hours
as a midlevel shortwave trough moves toward the Missouri-Kansas
border. Rain showers should exit then overnight tonight from west to
east as the stronger low-level moisture advection and aforementioned
shortwave depart into the lower Ohio Valley. There has been very
little to no change in the overall thinking of rainfall amounts.
Most locations should see 0.25-0.50" through tonight of beneficial
rain. A few lucky locations may see as much as 0.75" of rain as the
0Z HREF LPMM suggests.

Temperature wise, thick cloud cover (including low stratus for a
majority of the time) should really limit overall movement. Highs
today are forecast to be in the low 50s with lows in the upper 40s
to near 50 degrees tonight.


Gosselin

&&

.LONG TERM...  (Tuesday through Sunday)
Issued at 321 AM CST Mon Nov 24 2025

(Tuesday - Friday)

A cold front is forecast to move through the bi-state area Tuesday
afternoon/evening. A few stray showers may accompany this boundary,
but by and large mostly dry weather is forecast. Ahead of this
front, slightly warmer daytime temperatures are anticipated.
However, and stop if you haven heard this before, low stratus will
play a big factor. Model guidance has a strong signal for low
stratus through the afternoon hours. The HREF has probabilities (70-
100%) of 925-hPa relative humidity values over 90% through peak
heating (2100 UTC). Given this signal, did cool highs a couple of
degrees from the previous forecast. Highs are expected to range from
the mid 50s to low 60s, or about 6-8 degrees above normal for the
date.

All remains on track for a cold Canadian air mass to infiltrate the
mid-Mississippi Valley behind Tuesday`s cold front. The incoming air
mass has trended slightly colder over the past 24 hours. Mean 850-
hPa temperatures now are expected to drop into the -5 to -7C range
Thursday/Thursday night. Those values are within the 10th-20th
percentile of climatology. Given these trends, forecast high and low
temperatures have also decreased on average about 2-4 degrees. Highs
are expected to range from the mid 30s to mid 40s with lows in the
upper 10s/20s. These values would be about 6-10 degrees below normal
for late November. There still may be some more minor wiggle room to
come down with these temperatures too if these colder trends
continue. The current deterministic forecast highs/lows generally
lie closer to the 75th percentile of the NBM for reference.

There remains high confidence in a dry forecast Wednesday through
Friday, which is good news for any Thanksgiving holiday travel
plans. For anyone traveling Friday night into Saturday, that will
not be in the case.


(Friday Night - Saturday)

Deterministic model guidance all show a midlevel shortwave trough
moving across the south-central Plains toward the mid-Mississippi
Valley Friday night into Saturday, but vary with the strength of
this feature. The ECMWF and a majority of the EPS members show a
sharper trough, which in turn allows for stronger low-level moisture
convergence and more QPF. The GFS and most GEFS members are
flatter/weaker with the trough and associated moisture convergence
and have lighter amounts of precipitation. Given that this piece of
energy is still some 96 hours out from being sampled from the upper
air network, it is very difficult to say which scenario is more
likely to be correct.

What is more certain is that there should be very dry low/mid levels
of the atmosphere in place ahead of any precipitation. This may be
very critical as wetbulb temperatures are well below the freezing
mark, with the exception of the surface. However, even surface
wetbulbs are likely to be near or slightly below freezing across
basically the entire area. What does this mean? Well, it means that
as top-down saturation occurs temperatures will cool to their
wetbulb values. This process would favor the precipitation starting
as snow or changing from rain or a rain/snow mix over to snow as
temperatures fully wetbulb. Then the question becomes how long can
the precipitation remain snow? That is very difficult to say this
far out as persistent low-level southerly flow should warm
temperatures sufficiently to turn over the precipitation over to a
cold rain after a 3-9 hour period. The change to rain should be
fastest in southern areas and slowest the further north you head.

Given the expectation for the precipitation to be predominantly snow
for at least a few hours after onset, chances for our first
accumulating snow of the season are increasing. The 0Z LREF now
shows the chances for at least 1" of snow in the 30-70% from south
to north. A more substantial snow (>=3") may also be on the table,
especially for parts of northeast Missouri and west-central
Illinois. This is where chances approach 40% on the LREF. The EPS
shows low Extreme Forecast Index (EFI) 24-hour snowfall values (0.4-
0.5), but high shift of tails (SOT). This illustrates the
uncertainty well as less than half of EPS members show significant
snowfall, but some of the ones that do are quite extreme/heavy. In
fact, approximately 5-7 members (or 10-15%) of the EPS show greater
than 6" of snow. This is a time period that we will have to closely
watch over the coming days, especially with it being a heavy travel
day falling on the Thanksgiving weekend.


(Saturday Night - Sunday)

Forecast uncertainty is high to end the weekend (and into next
week). While ensemble guidance is in remarkably good agreement with
the strength of the southeastern CONUS mid/upper level ridge, the
spread is high with the magnitude of anomalous troughing across the
desert southwest and its evolution. The synoptic pattern is
favorable for a strong southwest-northeast oriented baroclinic zone
as more true arctic air attempts to press southeastward. Any piece
of energy that manages to eject out of the desert southwest should
produce widespread precipitation along/near the low-level baroclinic
zone. At this early juncture, the precipitation in our region is
more likely to be liquid rain than wintry, but sometimes arctic air
masses do manage to press further south and east than anticipated so
this will be another time period to monitor.


Gosselin

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1120 AM CST Mon Nov 24 2025

Widespread IFR/LIFR is largely gone from the region at this hour,
except in northern Missouri through central Illinois (including
KUIN) where stratus will linger. With abundant cloud cover
stunting temperatures and stratiform rain spreading areawide this
afternoon and evening, another round of low stratus will likely
cause renewed categorical restrictions tonight through the TAF
period. While fog will not be much of a concern with slightly
stronger wind speeds, a mix of mist and light rain will send VSBYs
down into IFR conditions along with the low stratus. Conditions
will gradually improve from west to east again tomorrow, though a
return to VFR conditions is not likely until at least late
afternoon Wednesday.

MRB

&&

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

$$

WFO LSX