838
FXUS63 KARX 070520
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1120 PM CST Sat Dec 6 2025

.KEY MESSAGES...

- Southern shift to tonight`s storm system is verifying in
  upstream observations, so have adjusted warnings and
  advisories accordingly. Heaviest snow tonight will be near
  Highway 18 in Iowa.

- Below normal temperatures persist throughout the next week
  with Tuesday being the "warmest" day with highs rising into
  the 30s.

- Additional snow chances continue into next work week. Rain
  will likely mix in with snow late Tuesday for areas south of I-94.

&&

.UPDATE...
Issued at 600 PM CST Sat Dec 6 2025

Upstream observations, radar imagery, and plow cameras in
Minnesota are verifying what we had worried about earlier in the
day...impacts on the north side of this winter system do not
appear to be verifying. Light snow is occurring, but impacts to
roadways looks to be minimal based on 511 page and traffic speed
reports. Therefore, have cancelled the northern row of counties
in the winter weather advisory along the I-90 corridor and
trimmed Mitchell County, IA out of the warning. Also adjusted
the end time of the hazards west of the Mississippi River given
that snow will be ending around midnight.

&&

.DISCUSSION...
Issued at 140 PM CST Sat Dec 6 2025

> WINTER STORM TONIGHT: taking a shift southward which would move
the bulk of the local snowfall along/south of I-90.

HRRR/RAP morning runs coming in with a distinct shift southward with
the winter storm track, more aligned with the very persistent,
consistent GFS and EC, which never wavered much from this southern
track. The HRRR remains even more aggressive with late morning/early
afternoon runs - pushing the snow farther south. RAP has been more
steady.

Ample lift in the projected snowband with sloping Fgen, isentropic
upglide on the 280:295K sfcs, favorable low level QG convergence,
and the parent shortwave itself. Some upper level jet support too.

DGZ mostly under 100 mb thick per RAP/HRRR soundings, but the SREF
suggests a decent shot (over 30%) for 1"/hour rates within the heart
of the band. EFIs are in the 0.7 to 0.8 range with a non-zero SoT in
the band. Still confident that 6+" amounts will be reached in the
band, less so in where that lays out.

With the CAMS aligning more with the global models...will shift the
snowband a bit farther south. HREF/REFS still painting a 20-40%
chance for 6+" of snow in the warning area of northeast IA across to
far southwest WI. Amounts less around I-90, more 1 to 3" range now,
but advisory still appropriate for this early season snowfall - and
higher impact area (interstate travel). PLan to "stand pat" with
current outlay of headlines for now. But, if the aggressive HRRR
trend looks like reality, some adjustments to the headlines will be
needed later this evening.



> NEXT WEEK: active pattern continues with periodic shots for
precipitation. Still trending cold for the most part, but Tue still
looking like a day many will warm above freezing.

Busy, progressive northwesterly flow a loft promises to spin a
multitude of shortwave troughs across the upper Mississippi river
valley. Some weak, some potentially strong.

On Mon/Mon night the GEFS and EPS continue to shift a couple weak
perturbations across the region, one more south, one more north. THe
northward shortwave looks a bit stronger and has a better chance to
lay down minor accumulations of snow Mon night. Favored track has
kept these chances across northern WI - and mostly away from the
local forecast area.

The next shortwave should pack more of a "punch" as it drives across
the northern plains Tue, spinning east/southeast across the region
Tue night. While the GEFS and EPS have been in good agreement with
relative strength and timing, positioning varies quite a bit -
between and within the model suites. Some keep the related pcpn band
across northern MN/WI. Others paint it across the local area. A few
push it even farther south into northern IA. On the whole though,
more favor a northern track.

There is surge of "milder" air ahead of the system which will
complicate ptypes. GEFS and EPS have inched up expected highs for
Tue over their last several runs with mid 30s now looking more
likely (60 to 80% chance to warm above freezing). Of course, these
temps reflect a more northward storm track. If it shifts south, so
will the milder air. The low level warming looks like a rain or snow
question at this time - not icy. Will let the model blend take the
reigns for ptype for now. Where it does snow, plenty of forcing with
deep QG convergence and sloping Fgen that a several inch band could
be realized.

Colder air surges in post the Tue night system and should hold temps
well below normal through the weekend. Other shortwaves will also
bring more snow chances here and there.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1118 PM CST Sat Dec 6 2025

IFR conditions associated with ongoing snow should continue for
the first 1-6 hours of the period, tapering off west to east
over that time frame. As snow departs, some MVFR ceilings may
remain briefly, but VFR conditions should return areawide by
12z. Remaining 18 hours should be VFR with relatively light
winds, a welcome change for aviation interests. Next chance for
reductions looks to be after 06z Monday when some low ceilings
may affect areas west of the Mississippi.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 AM CST Sunday for WIZ053>055-
     061.
MN...Winter Weather Advisory until 3 AM CST Sunday for MNZ094-095.
     Winter Weather Advisory until 6 AM CST Sunday for MNZ096.
IA...Winter Weather Advisory until 3 AM CST Sunday for IAZ008>010.
     Winter Weather Advisory until 6 AM CST Sunday for IAZ011-030.
     Winter Storm Warning until 3 AM CST Sunday for IAZ018-019-029.

&&

$$

UPDATE...Skow
DISCUSSION...Rieck
AVIATION...Ferguson