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FXUS63 KLSX 231129
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
529 AM CST Fri Jan 23 2026

.KEY MESSAGES...

- A potentially significant winter storm remains on track to bring
  widespread accumulating snow and travel disruptions to our area
  this weekend. While non-trivial uncertainties remain in the
  final timing and distribution of heavy snow, the most significant
  impacts are likely between late Saturday and early Sunday. Our
  ongoing Winter Storm Warning has been expanded slightly
  northward, and a Winter Weather Advisory was added for northeast
  Missouri and west-central Illinois.

- Bitter cold and dangerous wind chills are a near certainty
  between this morning and at least Saturday morning, with very
  cold conditions persisting through Monday.


&&

.SHORT TERM...(Through Sunday)
Issued at 407 AM CST Fri Jan 23 2026

All eyes are now fixated on the combination of bitter cold
temperatures and the approach of tomorrow/Sunday`s significant
winter storm, which remains likely to bring widespread impactful
snow accumulations to a large portion of the area this weekend.
While the shape of this storm and it`s potential impacts are
gradually becoming more clear, there are still some notable
uncertainties to discuss.

BITTER COLD:

Before we get to the snow, the first item on the agenda is the
approaching bitter cold arctic airmass, which is currently in the
process of rudely displacing yesterday`s much more seasonable
temperatures. This is all being driven by an exceptional arctic high
pressure system, which may reach above 1050 mb at it`s center by
later this afternoon. As of 2 AM, wind chills were already
uncomfortably well below zero across northeast Missouri and west-
central Illinois, and the combination of breezy north winds and cold
air advection will keep these values on a downward trajectory
through the middle of the morning. By then, wind chills north of I-
70 are likely to be -10 or less, and perhaps as low as -20 to -25 in
our northernmost counties. In fact, many areas today will see actual
temperatures only in the teens to even single digits, dropping to
near 0 overnight tomorrow. As such, the ongoing cold weather
advisory remains in effect along and north of I-70 from now until
midnight, and expands south into the rest of the area after midnight
through Saturday afternoon when wind chills finally "moderate" to a
still very cold 5 to -10 degrees. In sort, it`s going to be quite
cold through the weekend, with only very slight improvement Saturday
afternoon through Sunday.

HEAVY SNOW POTENTIAL:

By Saturday morning, attention turns to the approaching winter
storm, which remains largely consistent in its potential impacts
(and uncertainties) compared to the previous forecast. Much of the
area remains on track to see impactful snow accumulations, with
the heaviest snow still most likely to fall across southeast and
east-central MO, and southwest Illinois. It also remains likely
that the heaviest snow is likely to fall between Saturday evening
and Sunday morning when the strongest forcing arrives from the
southwest, and after very dry air is finally eroded.

On that note, this brings us to one of the most uncertain parts of
this forecast, which is the onset time of impactful snow. As
mentioned above, extremely dry low level air will be in place
Saturday morning, with near-record low surface dewpoints perhaps
as low as 20 to 25 degrees below zero thanks to the aforementioned
arctic high across the central CONUS. As warm air advection and
modest isentropic ascent begins to saturate the mid and upper
levels, snow falling into this extremely dry airmass will
initially struggle to reach the surface, and may not do so at
accumulating rates until sometime during the day Saturday, and
maybe not even until the afternoon/evening in northern areas. At
the beginning of the event, lift is not forecast to be
particularly strong, which will also likely limit precipitation
rates and make it difficult to erode this dry low level air.

Eventually though, this IS expected to occur across most of the
area, and once it does, very cold thermodynamic profiles with a deep
layer squarely within the dendritic grown zone are likely to support
efficient snow to liquid ratios (especially in northern areas),
although this will be quite variable. As such, mostly light but
still impactful snow is likely to start coating roadways by sometime
Saturday, with an emphasis on areas along and south of the I-70
corridor. Again, there is quite a bit of uncertainty regarding how
much of and exactly when this initial snow will reach the surface
during the first phase of this event, so those north of I-70 may
be waiting quite a while before they start to see actual impacts.

The next phase of the event begins late Saturday as a shortwave
kicks out of the Desert Southwest and Southern Plains, spreading
much stronger mid-level frontogenesis into the southern half of
Missouri and Illinois. This boost in lift is likely to produce much
more significant precipitation rates, and will also have much less
dry air to fight through after Saturday`s primer. As such, the
primary source of uncertainty Saturday night and Sunday lies more in
the track and strength of the shortwave (and developing surface low
to our southeast), and also the distribution of the most favorable
snow to liquid ratios.

As for the former, recent forecast trends have consistently brought
this feature into the area along a more favorable track for heavy
snow, with an emphasis on southeast Missouri, east central Missouri
(including the St. Louis metro area), and southwest Illinois. While
there is still some room for the track to shift, this has not
changed overnight tonight, and as a result Saturday evening through
Sunday morning remains the most likely period for heavy snow and
more significant impacts locally.

As for the latter, while at least some portion of the thermodynamic
profile will fall within the dendritic growth zone (-10 to -20 C) in
all areas, there will be some areas that will feature much more
efficient snow to liquid ratios than others. In particular, areas
roughly along and north of I-44 appear to have a much greater
overlap of saturation and lift within that favorable temperature
range, and will likely see the fluffiest snow as a result...but with
lower liquid equivalent amounts (QPF) holding accumulations back. On
the other hand, in southeast Missouri and southwest Illinois, models
continue to project persistent warm air advection aloft, and even
produce a narrow zone of above-freezing temperatures in the mid
levels even while maintaining very cold low level temperatures. This
continued trend suggests that some sleet will be possible in our far
southeast, and while that alone may not be enough to significantly
cut into snow totals given the higher precipitation rates expected
here, our snow to liquid ratios in this area may not be quite as
efficient. As such, it may end up that the sweet spot for the
heaviest snow falls somewhere in between, where higher
precipitation rates overlap with the more favorable thermodynamic
profiles for efficient snow rates (locally 1-2 inch per hour),
along with the potential for mesoscale bands as alluded to in the
previous forecast discussion.

Putting all of these details aside, confidence remains high that
much of the area will be impacted by significant snow accumulations
during this event, with widespread travel impacts expected. The most
significant impacts to travel are likely to occur between
Saturday evening and Sunday morning, when the heaviest snowfall
rates are expected. In spite of this growing confidence, there is
still some uncertainty regarding the final accumulation tally in
many areas...particularly in our north. Finally, impactful snow is
likely to taper off Sunday afternoon and evening, but some light
snow/flurries may linger into the overnight hours.

Considering all of the above, we have made the following changes to
our winter weather headlines to reflect our current thinking:

Most of the remaining Winter Storm Watch was upgraded to a Winter
Storm Warning starting at 9 AM Saturday and ending at 6 PM Sunday,
which is mainly narrow corridor of counties straddling I-70 in
central, east-central Missouri and central Illinois.

A Winter Weather Advisory was added for northeast Missouri and west-
central Illinois, also beginning at 9 AM Saturday and ending at 6
PM Sunday.

No changes were made to the already ongoing Winter Storm Warning, or
the ongoing Cold Weather Advisories.

BRC

&&

.LONG TERM...(Monday through Thursday)
Issued at 407 AM CST Fri Jan 23 2026

With attention squarely on our weekend snowstorm and bitter cold,
we have opted against a more detailed long-term forecast
discussion. However, the primary item of interest during the work
week will be the continuation of well below average temperatures
overall, with only brief moderation Tuesday before another
reinforcing shot of very cold air Wednesday onward. This will
have implications on the lingering snowpack, as areas that see
significant snow accumulations this weekend are likely to hold
snow cover through at least the end of the work week as a result.

BRC

&&

.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 525 AM CST Fri Jan 23 2026

While a major winter storm is on the way this weekend, the bulk of
those impacts are not expected to begin until after this TAF
period, and VFR conditions can be expected. Breezy northwest winds
and bitter cold can be expected throughout the TAF cycle, with
steadily lowering ceilings over the latter half of the period.
Still, VFR categories are expected to prevail through 12Z. Light
snow is expected to begin near or shortly after the end of the
period in central MO (JEF/SUS), but again most of this is expected
to hold off until later in the morning or early afternoon
Saturday.

BRC

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Cold Weather Advisory until 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 Warning from 9 AM Saturday to 6 PM CST Sunday for
     Audrain MO-Lincoln MO-Pike MO-Ralls MO.

     Winter Storm Warning from midnight tonight 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 tonight 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.

     Winter Weather Advisory from 9 AM Saturday to 6 PM CST Sunday
     for Knox MO-Lewis MO-Marion MO-Monroe MO-Shelby MO.

IL...Cold Weather Advisory until 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 Warning from 9 AM Saturday to 6 PM CST Sunday for
     Calhoun IL-Greene IL-Jersey IL-Macoupin IL-Montgomery IL-
     Pike IL.

     Winter Storm Warning from midnight tonight 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 tonight to noon CST Saturday
     for Clinton IL-Marion IL-Monroe IL-Randolph IL-Saint Clair
     IL-Washington IL.

     Winter Weather Advisory from 9 AM Saturday to 6 PM CST Sunday
     for Adams IL-Brown IL.

&&

$$

WFO LSX