849
FXUS63 KARX 090001
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
601 PM CST Mon Dec 8 2025

.KEY MESSAGES...

- Light snow moves into north-central Wisconsin this evening,
  continuing through the overnight hours. Accumulations around 1
  inch expected.

- Impactful winter weather is possible Tuesday afternoon into
  Wednesday. Accumulating snowfall is possible north of I-94
  where a Winter Storm Watch remains in effect for the potential
  for upwards of 6 inches of snow (30-50%). Snow accumulations
  are lower south of I-94 where a wintry mix is favored.

- Very cold temperatures for the end of the week. Highs will
  struggle to climb out of the single digits Friday and
  Saturday.

&&

.DISCUSSION...
Issued at 229 PM CST Mon Dec 8 2025

Today

For the rest of the day, some isolated to scattered flurries
are possible within the saturated low levels combined with
850hPa warm air advection moving through the region.

This evening and overnight, a shortwave trough currently over
southern Saskatchewan and Manitoba per water vapor imagery will
shift southeastward within the northwest flow regime in place.
With some modest moisture advection under currently southerly
winds, light snow is expected to develop overnight into Tuesday
across much of the region. However, amounts will be light with
the greatest accumulations expected for areas north of I-94
where accumulations around 1 inch are possible.

Following the snowfall overnight into Wednesday morning,
RAP/HRRR soundings indicate dry air beginning to work its way
into the region above -10C, resulting in a decrease of cloud
ice. This will coincide with forcing via continued warm air
advection and isentropic upglide on the 280K surface ahead of
the next system, which may be enough to result in periods of
light freezing drizzle as we head into Tuesday morning. This
could result in some slick spots for the morning commute before
deeper saturation moves east an hour or two after sunrise.

Impactful Winter Weather Tuesday Afternoon - Wednesday

A messy winter scenario sets up Tuesday afternoon into
Wednesday as a dynamic system develops across southern Canada
and the northern Great Plains before moving through the Upper
Midwest. A strong 500hPa shortwave trough deepens Tuesday in
association with the left exit region of a stout jet streak,
promoting upward vertical motion throughout the atmosphere
resulting in a deepening mid-latitude cyclone. The exact
location of this feature still remains somewhat in question, but
a slight southward shift has been noted in the recent GEFS/EPS
solutions.

As this winter system moves through the region, a plethora of
precipitation types are possible across the region. The
rain/snow delineation line sets up somewhere over the Upper
Mississippi River Valley, generally along a line from the Twin
Cities to far southwest Wisconsin. North of this line,
confidence is high that all snow will be realized and south of
this line all rain. However, it`s along the line and on the
leading edge of the snow that is the most uncertain owing to
850hPa warm air advection fluctuating thermal profiles. RAP/HRRR
soundings suggest a warm nose develops at 850hPa in response to
the warm advection, nudging above freezing in some locations.
This warm nose should be deep enough to melt hydrometeors
falling into it before then falling into a shallow cold layer
near the surface. This leads to the potential for freezing rain,
primarily for portions of northeast Iowa and southwest
Wisconsin where the 08.12z HREF suggests this potential is
highest. However, there soundings also indicate that periods of
nearly isothermal profiles along the 0C isotherm are possible
which would suggest snow is favored over freezing rain leading
to plenty of uncertainty in the ultimate precipitation type.

Overall, thinking that the majority of the region will see
either rain, snow, or a rain/snow mix, but there is the
potential for a few hours of freezing rain primarily over
northeast Iowa and southwest Wisconsin Tuesday afternoon and
evening before a transition to rain occurs across these regions.
Regarding the snowfall, areas along and north of I-94 have the
highest probability to see snowfall accumulations greater than 6
inches, 30-50% per the 08.13z NBM.

Apart from the messy precipitation type situation, a strong
low-level synoptic wind field sets up on the western and
southern sides of the low in response to the tightening pressure
gradient. Winds upwards of 50kts at 850hPa with a unidirectional
profile to the surface combined with steepening low level lapse
rates of 7-8C/km will allow efficient momentum transfer of
these winds to the surface across the region. Probabilities for
gusts greater than 40mph across southeast Minnesota, northeast
Iowa, and far southwest Wisconsin are currently situated at
20-40% in the 08.00z LREF, although are noticeable higher in
the 08.12z HREF which highlights 70-90%. The latitudinal extent
of the low will likely play into how windy our region gets. More
southerly and winds will skirt south, more northerly and winds
will likely increase.

Low level moisture lingers on Wednesday with saturation and
lapse rates reaching well into the DGZ. Some weak surface based
instability also develops, generally 40 J/kg or less. These
factors within cyclonic flow lingering over the region should
lead to some additional snow showers developing on Wednesday.

Very Cold Temperatures Late This Week

When all is said and done with the Tuesday/Wednesday system,
strong cold air advection takes hold, ushering colder air into
the region through the rest of the week. Temperatures
progressively drop Wednesday onward, currently expected to
bottom out Saturday. 925hPa temps fall to -18C to -22C overnight
Friday climbing only to -17C to -19C during the day Saturday
across the region in the 08.00z LREF mean, suggesting lows fall
into the teens below zero with highs struggling to climb out of
the single digits. Along with the very cold temperatures,
probabilities for wind chills of -25F or below sit at 40-60%.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 555 PM CST Mon Dec 8 2025

A round of light snow, possibly mixed at times with freezing
drizzle (20-30% chance), moves through the region overnight and
departs before sunrise. IFR conditions are most likely with the
passage of this snow, but some localized LIFR restrictions are
possible at a few sites. Conditions look to improve briefly
around midday Tuesday before another round of rain/snow arrives
in the afternoon--possibly mixed with freezing rain before
sunset--and lasts through the overnight. The heaviest snow is
forecast north of I-94 just after 00Z through the early morning
where IFR to LIFR conditions are expected.

Southerly winds this evening veer overnight to the southwest at
10-15G20kts, lessing and veering more to the west for the
morning on Tuesday before backing back to the south in the
afternoon. These winds quickly increase for Tuesday night,
though by how much is uncertain with a 30-50% chance of WNW gusts
in excess of 40-45 kts west of the Mississippi River overnight
into Wednesday morning.

An active weather pattern continues through the week with the
risk for aviation impacts for a time nearly every day into the
weekend.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 3 PM Tuesday to 6 AM CST
     Wednesday for WIZ032>034-042>044.
     Winter Storm Watch from Tuesday afternoon through late Tuesday
     night for WIZ017-029.
MN...Winter Weather Advisory from 3 PM Tuesday to 6 AM CST
     Wednesday for MNZ079.
IA...None.

&&

$$

DISCUSSION...Falkinham
AVIATION...Skow