471
FXUS63 KARX 080939
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
339 AM CST Mon Dec 8 2025

.KEY MESSAGES...

- Light snow moves into north-central Wisconsin tonight with accumulations
  of around an inch or less possible north of I-94.

- Impactful accumulating snow possible north of I-94 where a
  Winter Storm Watch is in effect for the potential of
  accumulations of up to 6 inches Tuesday afternoon through
  Tuesday night. Snow accumulations quickly diminish south of
  I-94 with a rain/snow mix favored.

- Very cold temperatures to end the week with highs struggling
  to get out of the single digits Friday and Saturday. Wind
  chills on Saturday morning may be 20 degrees below zero or
  colder.

&&

.DISCUSSION...
Issued at 339 AM CST Mon Dec 8 2025

Today - Tonight: Light Snow Chances in North-Central Wisconsin

A very subtle and weak shortwave can be noted on GOES-19 water vapor
imagery and RAP 500mb heights across southern MN this morning which
will slow push its way into the region for the morning and early
afternoon. While moisture is not very plentiful with this wave, the
very weak forcing may be just enough to develop a few flurries or
snow showers for the morning and early afternoon. Otherwise, a more
distinct wave will move through northern WI later this evening and
into tonight bringing a quick round of light snow, an appetizer if
you will, for north-central Wisconsin with accumulations of around 1
inch or less generally expected as probabilities in the recent HREF
have medium values (30-60%) for amounts of an inch or greater
through Tuesday morning in Taylor County.

Tuesday - Wednesday Morning: Rain/Snow South of I-94, Accumulating
Snow North of I-94

Tuesday and into Wednesday morning will be the main focus of this
forecast cycle as deterministic global models (GFS/EC/Canadian/NAM)
all agree on bringing a rather dynamic clipper system through
northern Wisconsin during the evening Tuesday and into the
overnight. The key question with this will be the precise location
of the attending surface low as any locations relative position to
the low will determine precipitation types and snow accumulation
potential. Overall, the frontogenetic forcing in the NAM appears
more disjointed and less defined in the 600-800mb layer than in
previous runs which in turn provides less confidence on the exact
duration of higher snowfall rates in the 1"+/hr range during the
evening on Tuesday. Much of forcing for this setup is more related
to isentropic upglide on the northeast sector of the low in
combination with some decent QG convergence in combination with the
very favorable synoptics. As mentioned earlier, still some
differences in the exact placement of this low with the operational
GFS attempting to bring accumulating snow all the way down to I-90
which is in contrast with the hi-res RAP/HRRR which pushes the
rain/snow line all the way into Taylor County. Overall though there
has been a general slight shift across much of the global ensemble
members.

In any case, currently have I-94 as the approximate delineation for
rain/snow and accumulating snow. Currently, probabilities in the
grand ensemble (GEFS/EC/Canadian ensemble) are fairly high (60-80%
chance) for amounts greater than 3" across Clark and Taylor
counties. The probabilities in this data for 5" or greater are lower
(20-40%), however these might be underdispersive given that the GEFS
has a much further south solution than the EC in their most recent
runs. As a result, given the synoptics with a fairly deep surface
low and fairly abundant moisture feeding into this system, have
opted to include Clark and Taylor counties in a Winter Storm Watch
in collaboration with surrounding offices as confidence is
increasing for impactful snow north of I-94. Further south, there
will be a sharp cutoff in snow amounts as more robust surface
warming will keep rain being the predominant precipitation type
south of I-94, assuming that model guidance does not continue to
shift south. Cannot fully rule out a brief period of freezing rain
on Tuesday afternoon south of I-94 before surface temperatures warm
up into the evening. However, confidence was not high enough (under
15% chance) at this time to include any mention in the forecast at
this point.

As we head into Tuesday night and early Wednesday morning, cold air
advection along with an increasing surface pressure gradient on the
western edge of the system will allow winds to increase across
portions of southeast MN and northeast IA. Consequently,
probabilities in the EC ensemble for wind gusts over 35 mph are high
(40-80%). Additionally, with steep low-level lapse rates, some
instability and low-level frontogenesis with the cold advection
early Wednesday morning, could see a period of snow showers with the
gusty winds as the cold advection pushes through. Overall,
accumulations south of I-94 with these snow showers would be fairly
minimal, on the order of a few tenths.

Wednesday - Saturday: Getting Progressively Colder

As we head into the second half of the work week, northwesterly flow
combined with the cold advection in the wake of our Tuesday system
will establish a persistent fetch of colder air into the region with
progressively falling temperatures through Saturday. As a result,
NBM generally progs highs on Wednesday from the 20s falling into the
single digits and low teens by Friday and Saturday. Overall Friday
and into Saturday looks like a fairly cold period overall as 850mb
temperatures depicted in the GFS/NAM reaching to around -20C.
Consequently, the grand ensemble (GEFS/EC/Canadian ensemble)
have already fairly high probabilities (50-70% chance) for wind
chills under -25F for Saturday morning with even a small chance
(10-20%) for wind chills colder than -35F in southeast MN. This
will be combined with likely (60-80% chance in the NBM) highs
only in the single digits above zero on Saturday. Needless to
say, this will probably be the coldest conditions we have
experienced so far this season.

As far as snow chances are concerned, it is difficult to pinpoint
any exact features with periodic bouts of surface high pressure
building into the region as well. However, given the northwesterly
flow and occasional weak perturbations that attempt to sneak through
the flow, would not rule out some snow chances late week, especially
on days where low-level lapse rates are steeper. As a result, the
grand ensemble has broad brushed medium to high probabilities (50-
70% chance) for measurable snowfall throughout this period across
the entire local area. Therefore have elected to hold onto the
precipitation chances in the NBM for Thursday and beyond.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1115 PM CST Sun Dec 7 2025

Primary concerns over the next 24 hours surround the arrival of
MVFR/IFR ceilings from the west and north and potential for
flurries and snow. Have stayed on the aggressive side of
aviation-tuned guidance for the arrival of low ceilings with IFR
eventually expected at RST. As for flurries, may see these
overnight through the mid-afternoon roughly along and west of
the Mississippi but have not included these in the TAFs due to
low confidence in both occurrence and timing. After 00z Tuesday,
more noticeable snow will overspread areas roughly north/east
of an EAU- LNR line but may extend farther west. Have thus
included a PROB30 for snow at LSE late in the period.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Storm Watch from Tuesday afternoon through late Tuesday
     night for WIZ017-029.
MN...None.
IA...None.

&&

$$

DISCUSSION...Naylor
AVIATION...Ferguson