327
FXUS63 KLSX 242324
AFDLSX

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

.KEY MESSAGES...

- Widespread showers are expected through tonight, with local
  amounts up to 0.25"-0.75" possible.

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

- Another round of precipitation, along with the first threat for
  accumulating snow across most of the region, arrives late Friday
  into Saturday.


&&

.SHORT TERM...  (Through Late Tuesday Night)
Issued at 251 PM CST Mon Nov 24 2025

The dense fog that plagued most of the region this morning
dissipated around 9am, with only a few spots still reporting any
fog or mist at this hour. Despite a gradually-strengthening
southerly wind at the surface, the widespread cloud cover is
stunting temperatures yet again today. Further west, a mid-level
wave is drawing Gulf moisture into the Mid-Mississippi Valley and
percolating widespread showers across southeast Kansas and
southwest Missouri. With moist isentropic ascent only
strengthening with time according to most available guidance, I
expect more widespread showers to envelop the region this
afternoon/evening from west (around 4pm) to east (around 7pm).
Instability of any consequence is very minimal, with HREF
probabilities of 100 J/kg of surface-based energy virtually zero,
so thunderstorms are not expected. Most areas will see upwards of
0.25" through early Tuesday morning, though there is a consistent
signal in most high-resolution guidance for a swath of 0.50"-1.00"
occurring coincident with the main thrust of mid-level forcing
and weak moisture convergence. Right now, that swath is forecast
generally along the I-44 corridor, but that may wobble north or
south by 30 or so miles in either direction.

As this wave departs Tuesday morning, a reinforcing shortwave is
universally modeled to dive south out of the northern stream through
the afternoon. A cold front accompanies it at the surface, forcing
some scattered light showers (30-40% chance), though the moisture
return by that point will be fairly weak. If rain does fall in any
one location, the probability of more than 0.10" is fairly low (10-
20%). What will be more noticeable and impactful is the gusty
northwest wind bringing an Arctic airmass and colder air (850mb
temperatures near the 10th climatological percentile) behind the
front, sending low temperatures 15-20 degrees cooler areawide
compared to lows tonight by most guidance. Sustained winds to 25mph
and gusts to 35mph can be expected, particularly across eastern
Missouri and most of Illinois where NBM probabilities of at least
35mph gusts Tuesday night into Wednesday are 80-90%.

MRB

&&

.LONG TERM...  (Wednesday through Next Monday)
Issued at 251 PM CST Mon Nov 24 2025

Temperatures for the busy pre-Thanksgiving travel on Wednesday will
be a bit more uncomfortable than recent days. As opposed to highs in
the mid/upper 50s on Tuesday, Wednesday will struggle to warm out of
the 40s with wind chills during the afternoon barely reaching 40
degrees. The strong gradient winds and gusts will continue through
the late morning, gradually weakening by sunset as the overall
system departs to the north and east. Nearly all available ensemble
guidance parks this Arctic airmass in place through Friday, with the
NBM interquartile range for high temperatures only 2-3 degrees
(indicating higher confidence in the cold air). Temperatures will
vary from north (upper 30s) to south (mid-40s) on Thanksgiving
itself, though mostly-clear skies will allow us to feel a bit warmer
outside. Weak but persistent cold-air advection at and near the
surface is evident in most available guidance Thursday night,
resulting in widespread subfreezing lows Friday morning (most rural
areas will fall into the mid-teens to mid-20s) and a marginally-
colder day Friday. Continued dry northwesterly flow aloft and an
absence of any strong forcing will keep us dry until at the earliest
late Friday evening.

Confidence continues to gradually increase in the first tangible
threat for accumulating wintry precipitation across the region this
season late Friday into Saturday morning. By this point, the flow
aloft will be gradually veering more southerly ahead of a shortwave,
though EOF patterns of the ensemble guidance show considerable
variability in the speed and amplitude of this wave. This
uncertainty will play a key role in the overall strength of the
system by the time it reaches us, though the precipitation type will
be governed more by the uncertain thermodynamic profile.
Deterministic guidance and ensemble counterparts show varying
thermal profiles and degrees to which a warm nose aloft will
develop.

What looks more likely than not (60-80%) is that most precipitation
will begin as snow overnight Friday. The strengthening moist
isentropic ascent evident in deterministic guidance would suggest a
lighter stratiform shield of snow for most, though nebulous 850-
700mb frontogenesis is also depicted and would suggest very brief
pockets of more moderate rates. While warm advection aloft does
strengthen as one goes through early Saturday morning in most
guidance, model soundings do show impressively-dry air beneath a
saturated DGZ by then as well. The question will be whether the
profile can wetbulb sufficiently to keep the column below freezing
by the time precipitation reaches the ground. Ensemble guidance is
fairly split on this detail, with 850mb temperatures (roughly where
the warm nose will be strongest) varying from a few degrees below
freezing (snow) to a few degrees above freezing (mostly rain). If
the colder solutions win out, widespread accumulating snow as far
south as the Ozarks would result. If the profile is warmer sooner in
the day, the accumulating snow would be more restricted in area and
mainly rain would fall for all others. The best potential for
accumulating snow and resultant minor travel impacts is across the
US-36 (MO)/I-72 (IL) corridor through early Saturday afternoon. It`s
also worth mentioning that if the antecedent cold air doesn`t
sufficiently cool the ground, warmer surface temperatures may work
against the potentially-light snowfall rates and result in
diminished impacts. Regardless, with this being a very busy travel
day and the first snowfall of note for many, additional caution
should be heeded.

A subtle warmup looks possible by Sunday with deeper southerly flow
in place, though the pattern gets far less predictable (and more
active) going into the first week of December. Early next week is
particularly volatile, with NBM high temperature IQRs ranging from
15-25 degrees and showing either a dramatic warmup or continued
cold. Precipitation chances stay in place amidst this dynamic wave
pattern, though snow chances beyond this weekend look unlikely (less
than 10%).

MRB

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 517 PM CST Mon Nov 24 2025

Impacts to terminals are expected to only worsen this evening and
overnight as a weather system pushes into the area. As it does so,
low-level moisture will increase, leading to drops in ceilings and
light rainfall. There are some embedded convective elements within
this rain, which may lead to visibilities briefly falling below
forecast values at times. Confidence is high that all terminals
will still see IFR flight conditions, with stratus for most sites
falling well below 1kft. The rainfall will only increase low-level
moisture, leading to fog development and it persisting once the
rain is done through the morning hours. Portions of the region
have a low chance of seeing visibilities less than 1 mile, and if
any local terminals are to be impacted by this, KCOU, KJEF, and
KUIN have the greatest chance. Confidence is low in conditions
improving much through the day tomorrow until a cold front sweeps
across the region late toward the end of the period.

Elmore

&&

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

$$

WFO LSX