502
FXUS63 KLSX 012337
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
537 PM CST Mon Dec 1 2025

.KEY MESSAGES...

- Light to moderate snow is expected this evening, before exiting from
  northwest to southeast. Additional snow amounts of 1-2" are
  expected.

- Seasonably cold temperatures will continue through the weekend,
  with another Arctic blast expected late Wednesday through
  Thursday.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 227 PM CST Mon Dec 1 2025

Moderate, to occasionally heavy, snow has moved east/northeast
over into west central and south-central Illinois and should exit
over the next 1-2 hours. There should be a 4-6 hour window with
lighter, spottier snow across much of the area this
afternoon/early evening. The exception is parts of northeast
Missouri and west-central Illinois where light to moderate snow
should be more continuous. Another round of light to moderate snow
should move northwest to southeast this evening across the entire
area. This snow will be aided by moderately strong low/mid level
frontogenesis and the main midlevel shortwave trough moving
through the region. Snowfall rates should be more modest than the
earlier round, generally in the 0.25-0.50"/hr range.

By the time the snow ends, a max band of 3-4+" is expected across
parts of central Missouri east/northeast into south-central Illinois
just north of the I-70 corridor. The snow amounts taper down sharply
once you head southeast of the I-70 corridor, as these areas saw
much lighter snow amounts this afternoon than neighbors further
north. For this evening`s round, additional snow of 1.0-1.5" should
be common for most of the area, with some totals as high as about 2".

The concern for Tuesday shifts to low-level clouds and temperatures.
Guidance is showing low stratus clouds to hang on well into the day
on Tuesday, particularly for parts of eastern Missouri over into
west central and south-central Illinois. Given that these locations
also have some fresh snow cover, temperatures should really struggle
to rise that much. Highs in the mid to upper 20s are forecast for
these areas. Further southwest, highs in the low to mid 30s are
expected in central and southeast Missouri. Parts of central
Missouri will have a snow pack, which could lead to slightly lower
high temperatures than forecast. There is more confidence in
southeast Missouri. This part of the CWA should not have as much
snow cover and should see some sunshine.


Gosselin

&&

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 227 PM CST Mon Dec 1 2025

(Tuesday Night - Wednesday)

Moderating temperatures are forecast heading into midweek as low-
level winds turn out of the southwest ahead of an approaching cold
front. Lows Tuesday night will still be cold however as a surface
ridge of high pressure works eastward into the Ohio Valley. Lows in
the mid teens to low twenties are forecast. Areas with still
(relatively) fresh snow cover though into south-central Illinois
still may not be cold enough. Winds shouldn`t pick up until after
0600 UTC, so we could see some single digits potentially. Highs on
Wednesday are expected to range from the mid 30s to mid 40s from
north to south ahead of the front. There is a bit more uncertainty
with highs in our far northwestern counties as the front should move
through there during the early afternoon. A slightly earlier (later)
passage could yield highs a few degrees colder (warmer) than
forecast.


(Wednesday Night - Thursday Night)

The arctic cold front will move through most of the CWA Wednesday
evening. Behind that front, a brief but strong push of unseasonably
cold air is expected. We also will have to watch for some light snow
to occur due to low/mid level frontogenesis behind the front. LREF
probabilities for measurable snowfall are in the 20-50% range across
the area. From past experience, these arctic fronts are efficient at
squeezing out some light snow. Any snow that does fall though would
likely be efficient (high SLR) and accumulate as temperatures
rapidly fall through the 20s. PoPs may need to be adjusted upwards
and expanded if this signal remains or increases in the next 24
hours.

Wednesday night`s lows will vary sharply from northwest to
southeast. Parts of northeast Missouri are expected to go below
zero, whereas lows in southeast Missouri and southwest Illinois are
forecast to be in the upper teens. Thursday is expected to be the
coldest day of the young winter season so far with highs ranging
from the mid teens to near 30 degrees from north to south.

Timing of the surface high does not look ideal at this point for
radiational cooling Thursday night as it quickly scoots out into the
Ohio Valley. This should keep lows in the single digits/teens across
the region.


(Friday - Next Monday)

Broad northwest flow aloft is expected this weekend into early next
week. Deterministic guidance shows multiple midlevel shortwaves
coming across the Mississippi Valley. These look like hybrid
clippers, with accumulating snow along/poleward of their tracks.
This far out, it is difficult to say when/where they will occur, but
climatology heavily favors these systems mostly impacting areas to
our north.

Temperature wise, largely below normal readings are forecast through
the period. The uncertainty comes with the individual clippers
themselves as they can yield higher temperatures than forecast ahead
of the, with colder temperatures in their wake. The latest NBM shows
the uncertainty well, with inter-quartile ranges for highs around 10
degrees.


Gosselin

&&

.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 534 PM CST Mon Dec 1 2025

Light snow is ongoing at KUIN and will spread into KCOU/KJEF over
the next 1-2 hours, followed by metro terminals between 0100-0200
UTC. The snow may intensify over metro St. Louis, and have TEMPOs
for 3/4SM. After a period of about 3-4 hours at any given
location, the snow will exit. IFR to low MVFR ceilings are
forecast overnight, and may linger through at least the morning
hours at KUIN and the metro sites.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory until midnight CST tonight for Crawford
     MO-Franklin MO-Jefferson MO-Lincoln MO-Saint Charles MO-
     Saint Louis City MO-Saint Louis MO-Warren MO-Washington MO.

     Winter Weather Advisory from midnight tonight to 3 AM CST
     Tuesday for Iron MO-Madison MO-Reynolds MO-Saint Francois
     MO-Sainte Genevieve MO.

     Winter Weather Advisory until 9 PM CST this evening for Audrain
     MO-Boone MO-Callaway MO-Cole MO-Gasconade MO-Knox MO-Lewis
     MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-
     Pike MO-Ralls MO-Shelby MO.

IL...Winter Weather Advisory until midnight CST tonight for Bond IL-
     Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Monroe IL-Montgomery IL-Saint Clair IL.

     Winter Weather Advisory from midnight tonight to 3 AM CST
     Tuesday for Clinton IL-Marion IL-Randolph IL-Washington IL.

     Winter Weather Advisory until 9 PM CST this evening for Adams IL-
     Brown IL-Pike IL.

&&

$$

WFO LSX