590
FXUS63 KARX 021129
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
529 AM CST Tue Dec 2 2025

.KEY MESSAGES...

- Light snow chances (20-40%) tonight and into Wednesday
  morning. Snow accumulations of a trace to 1/2" possible along
  and north of I-90.

- Very cold Wednesday night and into Thursday with wind chills
  of 10 to 25 degrees below zero Thursday morning. High
  temperatures on Thursday will remain in the single digits to
  lower teens for most.

- Additional snowfall possible Friday thru Saturday night. Probabilities
  are currently low (10-40% chance) for accumulations for an
  inch or greater across the area.

&&

.DISCUSSION...
Issued at 321 AM CST Tue Dec 2 2025

Today - Thursday: Light Snow Tonight, Very Cold Thursday

GOES-19 water vapor imagery and 02.06z RAP 500mb heights depict a
departing upper-level shortwave trough that will continue to push
east towards the Atlantic Coast. Behind this trough, northwesterly
flow situates itself across the local area for the day today with
temperatures falling to around the 10 degree mark. Given the shallow
cold air advection and relatively calm winds overnight, would expect
some freezing fog formation early this morning given the snowpack.
While probabilities in the recent HREF are low (10-30% chance) for
1/4-mile visibilities, would not rule out some pockets of this
especially given that Oelwein, IA has already observed 1/4 mile
visibilities. Otherwise, limited mixing and northwesterly flow will
keep our skies mostly cloudy with temperatures remaining below
normal with highs in the lower to middle 20s for today.

As we head into the overnight, a surface cold frontal passage will
instigate an area of light snow out ahead of it. Overall the forcing
is not overly impressive but with ample saturation, some of the CAMs
develop snow overnight. The probabilities for measurable snowfall in
the 02.00z HREF are modest (30-60% chance) near and north of I-90,
however for amounts greater than 0.5" are very low (0-20% chance).
Consequently, would expect some light snow to be around but
accumulations will likely be kept to only a few tenths tonight.

The bigger story as this front passes through will be the sharp drop
in temperatures. With high pressure building west of the local area,
this subsidence will allow cloud cover to clear out which will allow
for efficient radiational cooling Wednesday night and into Thursday
morning. As a result, median low temperatures during this period in
the NBM fall below zero areawide with even some potential for
temperatures to fall below minus 10 degrees across portions of
southeast MN. With still a lingering surface pressure gradient,
surface winds at around 10 mph will allow wind chills to fall to 10
to 25 degrees below zero. With the passage of the upper-level trough
that the aforementioned surface cold front was associated with,
reinforcing cold air advection in northwesterly flow will keep highs
on Thursday quite cold with median high temperatures in the NBM only
in the single digits to lower teens across the area. So be sure to
wear multiple layers and dress appropriately, particularly if
heading out on Thursday morning.

Friday - Sunday: Additional Snow Chances

By the time Friday rolls around, upper-level flow trends slightly
more zonal which in turn will allow our temperatures to "rebound"
slightly with highs back into the 20s for Friday. The main feature
that will be worth watching Friday and into Saturday will be a
shortwave trough that descends into the Great Plains. Overall timing
and location of this system remain in question as the strength of an
upper-level trough situated in Ontario will be key in how much room
to come north this wave has. Cluster analysis of the grand ensemble
(GEFS/EC/Canadian ensemble) would suggest one scenario (this one
currently seeming more likely with about 70% of members) where the
strength of the upper-trough and timing of the shortwave would be
favorable for bringing accumulating snow to the region as the
shortwave swings into the local area. In this scenario, roughly
30 to 60% of members bring an inch of snow or greater to the
local area. In other scenarios the shortwave gets pushed south
of the local area due to the upper-level trough being stronger
and would result in little snow for the local area. So,
certainly looks like the next period that could bring
accumulating snow but still much uncertainty on where this
shortwave tracks.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 529 AM CST Tue Dec 2 2025

MVFR to LIFR freezing fog coupled with low stratus will be the
primary aviation concern this morning. Main point of uncertainty is
exactly how low vsbys will get, primarily at KRST with the 02.00z
HREF keeping the LIFR vsby probabilities (10-20% chance at KRST)
further south of the TAF site. As a result, have kept with strictly
an IFR fog forecast with this forecast cycle. Regardless, low-MVFR
to IFR cigs will likely persist through much of the morning and into
the afternoon with low-level saturation in place. RAP/HRRR soundings
try to dry out the low-levels by later afternoon so have opted to
trend forecast in this direction, however am somewhat skeptical as
low-level moisture really struggles to mix out this time of year.
Regardless, additional category reductions are likely tonight as a
cold front progresses into the area bringing some possibility
for vsby reducing snow as well. Winds will start the TAF period
from the south and increase to around 8-12 kts by afternoon,
winds will then shift to the northwest with the approaching cold
front later tonight.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

DISCUSSION...Naylor
AVIATION...Naylor