Area Forecast Discussion

966
FXUS63 KLSX 230433
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1033 PM CST Thu Jan 22 2026

.KEY MESSAGES...

- Confidence continues to increase in a winter storm impacting
  portions of the area in the Saturday morning through Sunday
  timeframe. A Winter Storm Warning has been issued along/south of
  I-70 where confidence is highest in the heaviest snowfall
  occurring.

- Bitter cold temperatures will arrive tonight/Friday morning
  lasting through Monday. Wind chill values are expected to reach
  dangerous levels at times Friday morning through Saturday
  morning.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 327 PM CST Thu Jan 22 2026

A cooler airmass is in place compared to Wednesday, but insolation
has still allowed temperatures to warm into the 30s F. However,
behind a cold front passing through the CWA this evening, a strong,
Arctic, surface anticyclone (~1045 hPa) will quickly begin building
into the Mid-Mississippi River Valley tonight. Strong northerly low-
level CAA will cause temperatures to fall into the single digits F
to even below 0 F in locations north of I-70, where dangerous wind
chills of -10 to -25 F are expected Friday morning. With CAA
continuing through the day and upper/mid-level clouds thickening,
only a small diurnal rise in temperatures will occur. Although this
airmass will be anomalously cold (850-hPa temperature at 1st
climatological percentile), what is even more unusual is how dry the
airmass will be with dewpoints below -20 F. These values threaten
daily record low dewpoints at local climate sites, even coming
within 5 to 8 F of all-time records.

As any daytime insolation abates Friday evening and low-level CAA
persists, below 0 F and single digit F temperatures will further
invade the CWA Friday night into Saturday morning. With these
temperatures and northerly winds, dangerous wind chills of -10 to -
20 F will overspread nearly the entire CWA Saturday morning.

Pfahler

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 327 PM CST Thu Jan 22 2026

Concern continues to increase for a winter storm to impact the area
early Saturday through Sunday with accumulating snow that has the
potential to cause significant travel impacts where the heaviest
amounts fall. It is becoming increasingly clear that this event will
come in two rounds:  1.) a first round Saturday morning through
afternoon driven mainly by strong low/mid-level WAA/isentropic
ascent and upper-level level jet dynamics, and 2.) a second round
Saturday night into Sunday associated with the main upper-level
trough.

Most of the forecast uncertainty comes with this first round, due to
questions in how quickly the lower atmosphere moistens sufficiently
for snow to reach the surface and accumulate, especially considering
the potency of the low-level dry air. Currently, it appears that the
most vigorous forcing and moisture will pass through the southern
half of MO with uncertainty on how quickly low levels moisten around
the I-70 corridor and north, where it will likely take much
longer and some locations may not actually see any snow with this
first round. This notion is also supported by ensemble model
guidance 6-hour probabilities of more substantial QPF (>0.10")
being highest across southeastern MO/southwestern IL, relative to
the rest of the CWA. Model guidance is in agreement there will be
a relative minimum in large-scale forcing/ascent Saturday evening,
which will also lead to at least a lull in heavier precipitation.

The second round is anticipated to take place Saturday night into
the day Sunday. Given that large-scale ascent will be broader,
accumulating snow will be more widespread across the CWA through
this time. There are still some differences in exact upper-level
trough structure with it being composed by multiple embedded
shortwave troughs, but the general consensus among models is that a
gradually maturing low-level cyclone will track across the Lower
Mississippi River Valley and Ohio River Valley early Sunday. There
is variability in the track of this cyclone but an increasing
amount of ensemble model membership has an associated deformation
band translating northeastward through the CWA. Therefore, this is
the timeframe in which most of the CWA will see the majority of
its total snowfall. Confidence has decreased slightly in snow
being the only precipitation type across southeastern MO and far
southwestern IL with few of the extended CAMs indicating a warm
nose ahead of the cyclone causing the maximum temperature aloft to
straddle 0 C, leading to a low (

NWS LSX Office Area Forecast Discussion