Area Forecast Discussion

637
FXUS63 KLSX 142314
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
514 PM CST Wed Jan 14 2026

.KEY MESSAGES...

- Predominantly below average temperatures will prevail with the
  coldest temperatures expected Saturday through Tuesday,
  including below 0 F wind chills at times.

- There is a 50-60% chance of light snow Thursday night along/east
  of the Mississippi River with locally 1 to 2" of snowfall being
  the worst case (not most likely) scenario. Additional snow
  showers/flurries are favored at times Friday night through
  Saturday.


&&

.SHORT TERM...  (Through Late Thursday Night)
Issued at 218 PM CST Wed Jan 14 2026

Strong low-level CAA with gusty northwesterly winds (over 40 mph
early this afternoon) will continue into the evening. Daytime
insolation has stalled the impact of CAA, but cooling will increase
again through sunset with a handoff from CAA to efficient
radiational cooling overnight as a surface pressure ridge approaches
and winds become much lighter beneath a clear sky. The end result
will be low temperatures Thursday morning in the teens F--
approximately 40 F cooler than high temperatures were on Tuesday. On
Thursday, the pressure ridge will be shifting toward the east of the
CWA, enabling the onset of low-level WAA by the evening. However,
seasonably cold temperatures will persist through the day with WAA
not really being felt until evening and leading to temperatures
slowly warming through the evening and remaining steady or
continuing to warm Thursday night ahead of an approaching cold front.

Aside from temperatures, an upper-level trough is progged to
traverse northwesterly flow over the Mid-Mississippi River Valley,
forcing the cold front through the CWA early Friday morning and
providing some light snow driven by a tongue of moisture and strong
low/mid-level isentropic ascent Thursday night. There are still
small timing differences in model guidance, but the main
complicating factor is the presence of low-level dry air in many
forecast soundings that will need to be overcome before snow will be
able to reach the surface. Global model ensemble and HREF 24-hour
probabilities of measurable precipitation are 50 to 80 percent
along/east of the Mississippi River, indicating where confidence is
highest that dry air will be overcome. Given the transient nature of
the light snow and its parent forcing, precipitation may fall
entirely within a 3 to 6-hour window which will limit overall
snowfall amounts. This is especially considering some of the snow
will need to go toward sufficient moistening and most of the
moisture and forcing is focused below the DGZ. The 90th percentile
of QPF is up to 0.10" along/east of the Mississippi River which
represents a worse case scenario of snowfall up to locally 1 to 2"
considering SLRs around 10 or 12:1. In this case, minor impacts are
possible for the early Friday morning commute, but on the other hand
the 10th percentile of QPF is 0.01" or less, which would mean little
snow and no impacts.

Pfahler

&&

.LONG TERM...  (Friday through Next Wednesday)
Issued at 218 PM CST Wed Jan 14 2026

The airmass behind the early Friday morning cold front will be
relatively mild and allow for high temperatures on Friday to
actually warm to above average and in the 40s F with post-frontal
low-level flow possessing a large westerly component. These
temperatures will be the calm before a true bite of Arctic air
arrives Friday night...

Upper-level cyclonic, northwesterly flow will persist through Friday
and the weekend as longwave troughing dominates the Great Lakes
Region. The first in a parade of shortwave troughs will arrive
Friday evening, facilitating the passage of an Arctic cold front
Friday night. This pattern will be favorable for waves of snow
showers and flurries through Saturday, especially with the front
itself given that will be when low-level forcing and instability is
strongest. Swaths of light accumulations could result where snow
showers are more persistent, which is reflected by global model
ensemble 24-hour probabilities of measurable snow 50+ percent broad-
brushed across the CWA. Additionally, strong CAA will bring 850-hPa
temperatures below the 2.5th climatological percentile by Saturday,
translating to high temperatures in the upper teens and 20s F.

There are still timing differences on the passage of another Arctic
front on Sunday, leading to around a 15 F interquartile high
temperature range in the NBM from values similar to Saturday to
milder temperatures closer to average in the prefrontal "warm"
sector. Other than this potential on Sunday, confidence is
increasing that very cold temperatures will persist into early
Tuesday. The exact magnitude of the cold is still not quite certain,
but Sunday morning and Tuesday morning both stand out as the coldest
times of the period when both the brunt of the Arctic airmasses will
be present and surface anticyclones will be favorably placed. The
ultimate position of these features will determine precise
temperatures with NBM low temperature interquartile ranges spanning
between just below 0 F and the mid-teens F (coldest along/north of I-
70). These temperatures are cold enough that even with light winds
wind chill values could fall below 0 F, with probabilities of -10 F
based on ensemble model guidance 15 to 30 percent across
northeastern MO/west-central IL during the mornings Sunday through
Tuesday. Global model guidance suggest that there will be enough
adjustment in the upper-level pattern Tuesday onward, that
temperatures will moderate but by exactly how much is not clear.

Pfahler

&&

.AVIATION...  (For the 00z TAFs through 00z Thursday Evening)
Issued at 511 PM CST Wed Jan 14 2026

Dry and VFR conditions will persist through the TAF period.
Today`s gusty winds will continue to slacken tonight. Tomorrow,
winds will back to southerly with the arrival of surface high
pressure. Mid-level clouds will begin to filter in tomorrow
afternoon ahead of a system forecast to produce light snow mainly
east of the Mississippi River. This system falls just beyond the
current TAF period.

Jaja

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion