Area Forecast Discussion

255
FXUS63 KLSX 152337
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
537 PM CST Thu Jan 15 2026

.KEY MESSAGES...

- A brief period of light snow is expected this evening into
  overnight, mainly across IL with around a dusting up to 0.5" of
  accumulation.

- Scattered snow showers will accompany an Arctic cold front
  Friday evening. Brief bursts of snow could occur with limited
  visibilities and a quick dusting. Localized amounts of up to
  0.5" are possible where snow showers train or repeat.

- A period of very cold temperatures is forecast Saturday through
  Tuesday, including sub-0 F wind chill values likely each
  morning north of I-70.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 228 PM CST Thu Jan 15 2026

A surface pressure ridge will continue to advance to the east of the
CWA this evening with low-level WAA. Despite full sunshine, this
process has been slow with temperatures gradually warming into the
30s F through evening from west to east. Temperatures will remain
warmer than last night with WAA continuing ahead of an approaching
cold front. This front is associated with an upper-level shortwave
trough crossing from Canada into the Northern Plains. A tongue of
low/mid-level moisture and isentropic ascent will drive an area of
light snow that tracks through the CWA this evening into overnight.
A low-level layer of dry air (surface dewpoints starting around the
10th climatological percentile) will still be an issue for this snow
to reach the surface and accumulate. For many locations this will
prevent snow being more than flurries, but HREF probabilities of
measurable snow are 60 to 90 percent across west-central/south-
central IL, reflecting where confidence is higher that dry air will
be overcome. Considering moisture and forcing will be mostly below
the DGZ and the fact that snow will fall within, at most, a 3-hour
window, around a dusting to 0.5" of accumulation is expected across
IL. This snow could be enough for localized minor impacts.

The aforementioned cold front will pass early Friday morning, but
low-level CAA in its wake will be weak and gradual with a large
westerly component to flow, allowing temperatures to warm into the
40s F across much of the area through midday. However, an Arctic
cold front will crash through the CWA Friday evening, marking the
arrival of a much colder airmass. Large-scale ascent from the
attendant shortwave trough and low-level forcing with the cold front
will serve as catalysts for scattered snow showers spreading
southeastward through the CWA Friday afternoon into night. A few
showers ahead of the front could contain rain or graupel, but snow
will be predominant as wet-bulb zero heights fall upon FROPA. There
is enough steep low-level lapse rates, instability, and forcing that
brief bursts of snow could occur with lower visibilities and a quick
dusting. Much of the CWA will likely see at most a dusting from
these snow showers, but there could be a few localized swaths where
snow showers train/repeat and produce up to a 0.5" of accumulation.
All these factors point to localized impacts to the latter parts of
the evening commute on Friday.

Pfahler

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 228 PM CST Thu Jan 15 2026

Strong low-level CAA will continue to usher a very cold, Arctic
airmass into the Mid-Mississippi River Valley on Saturday with 850-
hPa temperatures falling below the 2.5th climatological percentile.
This will be the beginning of an extended period of cold that will
persist through early Tuesday, reinforced by another Arctic cold
frontal passage Sunday evening. NBM interquartile temperature ranges
(IQRs) have contracted to 7 F or less, indicating increasing
confidence in exact temperatures through the period with high
temperatures mainly in the 20s F and low temperatures largely in the
single digits and teens F. The presence of nearby Arctic surface
anticyclones both Sunday morning and Tuesday morning support those
being the coldest mornings with even 10 percent probabilities in
global ensemble model guidance for sub-0 F low temperatures across
northeastern MO/west-central IL Tuesday morning. With these
temperatures and even just light winds, probabilities of sub-0 F
wind chill values are also around 50 to 80 percent north of I-70
each morning Sunday through Tuesday. Probabilities of wind chill
values below -10 F are also 20 to 40 percent in northeastern MO/west-
central IL Monday morning when winds will be stronger, but
confidence is low that values will reach Cold Weather Advisory
Criteria for those areas (-15 F or colder) at this point. Largely
dry conditions are expected during this period as well but flurries
will be possible at times.

Global model guidance is coming into better agreement Tuesday onward
that upper-level longwave troughing over the Great Lakes Region will
weaken and/or shift eastward. This process would permit rising
heights across the Mid-Mississippi River Valley and low-level
northerly/northwesterly flow to finally open to the west or
southwest leading to warming temperatures. Exactly how quickly and
dramatically this process takes place is still not completely clear
with NBM temperature IQRs around 7 to 10 F--a difference between
reaching slightly below average temperatures and above average
temperatures.

Pfahler

&&

.AVIATION...  (For the 00z TAFs through 00z Friday Evening)
Issued at 530 PM CST Thu Jan 15 2026

Light snow is moving through northeast MO as of 2330z.
Observations and areal cameras show that little to no snow is
reaching the ground. As snow pushes southeast tonight, some
locations mainly east of the Mississippi River may see brief,
light snow. A cold front passing during the period will cause
southerly winds to veer to westerly tomorrow morning and become
gusty. Brief snow showers capable of light snow and reduced
visibilities are forecast tomorrow night. Confidence in direct
impacts to terminals is low.

Jaja

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion