Area Forecast Discussion

325
FXUS63 KLSX 111027
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
427 AM CST Thu Dec 11 2025

.KEY MESSAGES...

- Dangerous cold is expected this weekend. The most brutal wind chills
  will be north of I-70 Sunday morning.

- Light snow will glance portions of northeast Missouri and central/west-
  central Illinois this afternoon into tonight. The chance of
  significant impacts is low, but a small shift southwest could
  result in accumulations of 1"-2".

- Measurable snow is expected (80 - 100%) north of I-70 on Saturday.
  Any snow that falls will stick and cause travel impacts.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 314 AM CST Thu Dec 11 2025

The focus for today - Friday is the potential for light snow in
northeast Missouri southeastward through south-central Illinois in a
corridor roughly extending from Quincy, IL to Salem, IL and
northeast. The clipper responsible for the snow has been trending
southwest over the past day or so, placing the stripe of higher snow
accumulations on our northeastern doorstep. The latest 00z 12/11
HREF notably does not continue this southwestward trend, and the 00z
LREF actively pushes it back north. The majority of CAMs reflect
this as well, having the snow gradient just along our border with
higher reflectivity glancing in every now and again. This gradient
is expected to be tight, so where it places does matter. The latest
HREF LPMM gives us an idea of an "extreme" scenario. Currently this
extreme is completely northeast of our CWA, which reflects the
decreasing probabilities of 24 hour snowfall >1" (20 - 30% from 30 -
50%). However, the footprint is not gospel, and may (although not
climatologically favored) still shift southwest. It would only need
to shift a couple dozen miles to dramatically increase the chance of
accumulating snow. In this case, 1-2" will be possible in the
aforementioned corridor. Very brief periods of sleet are also
possible with any snow that falls, but are not expected to cause
impacts.

Jaja

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 314 AM CST Thu Dec 11 2025

A brutal, anomalously cold airmass will follow the Thursday night
clipper. Temperatures will begin to fall as early as Friday
night, but the brunt of the cold will be felt Saturday night
through Sunday night with an emphasis on Saturday night. The once
warming NBM has consistently cooled over the past 2 days, with
KUIN dropping from a Sunday forecast high of 15-20 degrees to a
new high of 9. Given the strength of the Arctic air (850 mb temps
within the 10th percentile of climatology) and the strength of the
surface high pressure (97.5th percentile of climatology), and the
increasing likelihood of a snowpack, I think the NBM is on the
right track, even if its Saturday and Sunday night lows are still
above the 50th percentile. Despite potentially having more room to
drop, Saturday`s forecast overnight lows and wind chills will be
bitterly cold. LREF probabilities of 6am Sunday wind chills 

NWS LSX Office Area Forecast Discussion