074
FXUS63 KLSX 230011
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
611 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 (<20 percent) chance of sleet
mixing with the snow, but it does not appear likely that this will
significantly cut down on snow totals there. Accumulating snow is
expected to gradually end midday Sunday through the afternoon,
but light snow or flurries could linger into the evening with
large-scale ascent gradually diminishing but deeper moisture
lagging.

One unique aspect of this event will be the aforementioned bitter
cold airmass in place that aids in a deep, isothermal layer
extending through a vertically elongated dendritic growth zone (DGZ),
supporting above average SLRs of anywhere from 12 to 18:1. However,
in these cases crystal habits may become more important for SLRs,
which could lead to SLRs varying spatially and temporally, maximized
where the strongest FGEN/ascent exists in enhanced banding. These
bands are still difficult to pin down at this point but could result
in 1"/hour snowfall rates at times. In terms of total snowfall,
there has been a continued northward trend in model guidance in the
last 24 hours, which has allowed confidence to sufficiently increase
along/south of I-70 for the Winter Storm Watch to be upgraded to a
warning. The rest of the Winter Storm Watch has been extended
another tier or two of counties northward where onset time should be
later and there could a relatively sharp northern cutoff in snowfall
totals, driven by differing snowfall durations and snowfall
efficiency (i.e., spatially varying SLRs discussed above).
Probabilistic snowfall data includes 90 percent chances of 4"+
snowfall along/south of I-70 and even 60 to 70 percent chances of
8"+ of snowfall. Significant travel impacts are expected where the
heaviest snow falls, most likely in the Winter Storm Warning area,
but even lighter snow will be able to cause minor impacts since it
will readily accumulate on cold surfaces.

The bitter cold airmass will remain in place through at least
Monday, with clearing clouds, fresh snow cover, and a nearby surface
anticyclone favoring efficient radiational cooling Sunday
night/Monday morning. Probabilities of sub-0 F low temperatures are
50 to 70 percent across nearly the entire CWA, and have been
increasing as probabilities of more substantial snow cover increase.
Some moderation is expected through mid-week next week, but it is
uncertain if temperatures will warm above 32 F, with corresponding
probabilities only 30 to 50 percent across southeastern MO Tuesday
and Wednesday.

Pfahler

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 556 PM CST Thu Jan 22 2026

A cold front will move through the area from northwest to
southeast tonight. Winds will turn to the northwest behind the
front with gusts around 20 knots through much of the day on
Friday.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Cold Weather Advisory from 3 AM Friday to noon CST Saturday for
     Audrain MO-Boone MO-Callaway MO-Knox MO-Lewis MO-Lincoln MO-
     Marion MO-Monroe MO-Montgomery MO-Pike MO-Ralls MO-Shelby
     MO-Warren MO.

     Winter Storm Watch from late Friday night through Sunday
     afternoon for Audrain MO-Lincoln MO-Monroe MO-Pike MO-Ralls
     MO.

     Winter Storm Warning from midnight Friday night to 6 PM CST
     Sunday for Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Iron MO-Jefferson MO-Madison MO-
     Moniteau MO-Montgomery MO-Osage MO-Reynolds MO-Saint
     Charles MO-Saint Francois MO-Saint Louis City MO-Saint
     Louis MO-Sainte Genevieve MO-Warren MO-Washington MO.

     Cold Weather Advisory from midnight Friday night to noon CST
     Saturday for Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Madison MO-Moniteau MO-Osage MO-
     Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis
     City MO-Saint Louis MO-Sainte Genevieve MO-Washington MO.

IL...Cold Weather Advisory from 3 AM Friday to noon CST Saturday for
     Adams IL-Bond IL-Brown IL-Calhoun IL-Fayette IL-Greene IL-
     Jersey IL-Macoupin IL-Madison IL-Montgomery IL-Pike IL.

     Winter Storm Watch from late Friday night through Sunday
     afternoon for Calhoun IL-Greene IL-Jersey IL-Macoupin IL-
     Montgomery IL-Pike IL.

     Winter Storm Warning from midnight Friday night to 6 PM CST
     Sunday for Bond IL-Clinton IL-Fayette IL-Madison IL-Marion
     IL-Monroe IL-Randolph IL-Saint Clair IL-Washington IL.

     Cold Weather Advisory from midnight Friday night to noon CST
     Saturday for Clinton IL-Marion IL-Monroe IL-Randolph IL-
     Saint Clair IL-Washington IL.

&&

$$

WFO LSX