Area Forecast Discussion

381
FXUS63 KLSX 282121
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
321 PM CST Wed Jan 28 2026

.KEY MESSAGES...

- Another Arctic airmass will begin moving into the area Thursday.
  Temperatures will become much colder with highs struggling into
  the teens to low 20s Friday and Saturday. Overnight lows will
  be near zero with wind chill values dropping to 5 to 15 degrees
  below zero.

- There is a 20-40% chance for light snow Thursday afternoon and
  evening. Most locations will see little to no accumulation,
  however, localized accumulations up to 1 inch are possible.

- There is another chance for light snow Sunday, mainly along and
  north of I-70.

&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 303 PM CST Wed Jan 28 2026

The primary concern in the short term is the potential for
accumulating snow Thursday afternoon through Thursday night.  A
short wave which is currently over the Rockies will continue moving
east into the central Plains by tomorrow morning.  It will then clip
southwest Missouri Thursday afternoon/evening and continue east-
southeast through Thursday night.  The low level reflection of the
wave takes a similar path through Thursday night, and produces some
850 warm advection, mainly along and south of I-70.  Between the
warm advection and mid-level frontogenesis, most deterministic
guidance is now producing light QPF over the area.  Additionally,
the LREF and NBM are now showing 20-60 percent probabilities of >0.1
inch of snow across most of the area.  As all this occurs, another
Arctic airmass will build south into the Mid Mississippi Valley from
the Upper Midwest. Forecast soundings indicate the column will be
more than cold enough for any precipitation that falls will be snow,
with the possible exception of southeast Missouri on Thursday night.
 The saturated layer only reaches up to 850-800mb and is not quite
cold enough to support ice crystal growth, so there is a chance that
the precipitation could begin as freezing drizzle. However there is
another saturated layer above 700mb where guidance is showing lift.
Could therefore see a seeder-feeder scenario where ice crystals fall
from farther aloft and grow in the lower level saturated layer.  At
any rate, the QPF is very light, and spotty for the most part.
Current thinking is that if it snows, most locations will receive
little if any accumulations. However some steadier and more
persistent snow could fall where frontogenesis produces banding,
which could produce accumulations up to an inch. With all this in
mind, have bumped up PoPs to 20-30 percent Thursday afternoon along
and north of I-70 with the primarily frontogenetical forcing, and 20-
40 percent on Thursday night across the rest of the area. One way or
another, it will be cold enough that every flake of snow will
accumulate and produce slick spots on roads.

Carney

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 303 PM CST Wed Jan 28 2026

The remainder of the forecast remains basically unchanged.  The
upper level pattern will amplify Friday through Sunday with a deep
long wave trough over the eastern U.S. and a ridge over the west.
This allows a 1040+mb Arctic high to settle into the Great
Plains. Highs Friday and Saturday will struggle into the teens and
20s with lows between 0 and 5 above. There may be some snow
showers late Friday afternoon/Friday evening as a vigorous short
wave moves through the Mid Mississippi Valley. GFS forecast
soundings show steep low level lapse rates developing Friday
afternoon and persisting into the evening. Deterministic guidance
does produce some very spotty QPF, however the ensemble
probabilities of 0.1 inch of snow don`t exceed 20-30 percent and
in most cases are much lower so have not added any additional snow
to the forecast on Friday or Friday night.

Another short wave trough moves across the Midwest Sunday into
Sunday night.  Warm advection ahead of the trough produces another
chance for precip, mainly across northeast Missouri and west central
Illinois.  However, the GFS and ECMWF do not agree that precip will
even occur, and the LREF only shows a 20-40 percent chance of >0.1
inch of snow.  Have therefore left the 20-30 PoPs in the current
forecast alone.  The GFS and deterministic NBM show temperatures
becoming milder early next week as the Arctic high moves east and
low level southwesterly flow brings warmer air to the Mid
Mississippi Valley.  However the ECMWF drags another cold airmass
into the Midwest early next week behind Sunday`s short wave.  With
little agreement between deterministic guidance, have stuck with the
warmer NBM solution for now.

Carney

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1135 AM CST Wed Jan 28 2026

VFR flight conditions are expected to prevail through the period.
Light and variable winds will turn to the northeast overnight as
high pressure builds across the Midwest.

Carney

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion