746
FXUS63 KARX 152342
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
542 PM CST Mon Dec 15 2025

.KEY MESSAGES...

- Much warmer early this week with highs in the middle to upper
  30s for Tuesday and Wednesday.

- Rain moves into the area Wednesday night and continues into
  Thursday where a changeover to snow occurs before
  precipitation exits. The probability for snow accumulations of
  1 inch or greater are very low (under 20% chance).

- Cold for Friday morning with low temperatures around the 0
  degree mark.

&&

.DISCUSSION...
Issued at 148 PM CST Mon Dec 15 2025

Rest of Today - Wednesday: Warming Trend, Fog Tonight South of
I-90

We say goodbye to the bitter cold from over the weekend today as the
upper-level trough responsible depicted on GOES-19 water vapor and
15.15z RAP 500mb heights is now situated over the eastern CONUS.
Consequently, our area is currently being subjected to northwesterly
flow, however upper-level ridging to our west in combination with
southerly return flow will push fairly decent warm air advection
into the area over the next 24 hours. This will likely result in
some fog formation overnight with the present snowpack in place
along with light surface winds. Currently, the 15.12z HREF has
medium probabilities (30-60%) for visibilities of a quarter mile or
less, primarily south of I-90 so cannot rule out some pockets of
dense fog, albeit these probs might be overdone with the present
snowpack.

As we head into Tuesday, 850mb temperatures increase sharply to
around 10C as depict in deterministic models which is quite
impressive for this time of year with it running at around the 99th
percentile in NAEFS guidance. That being said, the persistent
snowpack and low-level cold layer will keep our temperatures from
warming as efficiently with the inter-quartile range for high
temperatures in the NBM holding firmly in the middle to upper 30s.
Additionally, with an upper-level trough passage generally to the
north of the region on Tuesday night and into Wednesday, really not
expecting much for precipitation potential through the daytime hours
on Wednesday.

Wednesday Night - Friday: Rain/Snow, Much Colder Friday Morning

Our next weather system to watch will begin to push into the local
area on Wednesday night as an amplifying shortwave trough will push
through Alberta/Saskatchewan and into the Dakotas on Thursday. As
this occurs, southerly moisture advection in combination with
fairly decent QG convergence and cold advection with a passage cold
front will result in decent forcing for precipitation overnight
Wednesday and into Thursday. Ahead of the cold advection associated
with this system, warm surface temperatures in the middle 30s would
suggest a predominant rain precipitation type considering 850mb
temperatures in the GFS/EC sit around the freezing mark until the
cold advection kicks in during the afternoon on Thursday. As the
main trough axis pivots overhead, sharp cold air advection will
quickly knock down temperatures over the course of the day on
Thursday and shift the low-levels into the dendritic growth zone. As
a result, would expect a changeover to snow during the day on
Thursday before precipitation exits. Overall though, minimal
accumulations are expected with this system across the area with
very low probabilities (0-20% chance) for an inch of snow or greater
during the day on Thursday within the grand ensemble
(GEFS/EC/Canadian).

Behind the cold front, an increasing surface pressure gradient and
low-level winds at 850mb to around 40-45 kts will allow for some
breezy conditions with the momentum transfer within the cold
advection regime. Consequently, the EC ensemble has fairly
respectable probabilities (50-70%) for wind gusts over 35 mph across
portions of northeast IA and southeast MN for Thursday evening. By
the time Friday morning rolls around, temperatures will drop fairly
rapidly with the core of 850mb temperatures within the airmass
falling to around -20C shown in the GFS/EC. Consequently, the inter-
quartile range for morning lows on Friday in the NBM range from
anywhere in the single digits above and below zero. With winds still
remaining somewhat breezy, wind chills could fall to around the -10F
to -20F mark on Friday morning. Thankfully this round of cold will
be very short-lived as returning southerly flow will bring warm air
advection back into the region with highs reaching into the 20s
south of I-94. Have some small snow chances (15-20% chance) north of
I-90 later Friday with this warm advection, however probabilities
for snow accumulations of an inch or greater are extremely low
(under 10% chance) for the entire local area.

This Weekend: Seasonable with Minimal Precipitation Chances

On Saturday, the aforementioned warm advection will continue to push
into the region which in turn will increase our temperatures back
into the 30s with median high temperatures in the NBM ranging from
the upper 20s to middle 30s across the area. However, after the
passage of a shortwave north of the area, northwesterly flow will
briefly return to the region cooling temperatures back down for
Sunday. Currently, have some slight precipitation mention (~15%
chance) at times during this period in accordance with the NBM.
However, given the fast progressing nature of this wave and with the
bulk of the more robust forcing in deterministic guidance staying
north of the region, not overly confident in any meaningful
accumulations with the probability for measurable snow in the grand
ensemble (GEFS/EC/Canadian) remaining low (10-30% chance) at this
time through the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 533 PM CST Mon Dec 15 2025

Potential fog remains the primary concern in the aviation
forecast. Still thinking areas in NE IA will likely see
visibility under 1SM while farther north to the I-90 corridor,
uncertainty still remains. Have continued to hold mentions of
fog at RST/LSE but, given trends in latest guidance, have kept
these mentions VFR with this update. Fog should first form in
central IA to central MN, so will closely monitor and amend
ahead of the 06z cycle if necessary.

&&

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

&&

$$

DISCUSSION...Naylor
AVIATION...Ferguson