262
FXUS63 KARX 091743
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1143 AM CST Tue Dec 9 2025

.KEY MESSAGES...

- This afternoon into Wednesday morning brings multiple
  winter weather hazards to the region. Heavy snow is expected
  north of I-94 this evening with up to 6 inches falling in 4-6
  hours. South/west of I-94, a period of light freezing rain and
  cold rain is expected this evening followed by a short break
  until, between midnight and 6 AM Wednesday, strong winds and a
  brief burst of intense snow showers is expected. Along I-94,
  largely snow will occur but a glaze of ice may also occur as
  well.

- Very cold temperatures for the end of the week. Highs
  will struggle to climb out of the single digits Friday and
  Saturday. Morning wind chills of -25 or lower possible.

&&

.DISCUSSION...
Issued at 357 AM CST Tue Dec 9 2025

Winter storm this afternoon into Wednesday morning

08z WV satellite shows a shortwave over western British Columbia
with a broad upper jet on the equatorward side of this feature
extending over WA/OR east to ND/SD. Surface lee cyclogenesis has
begun in southern Alberta as a result. Across our CWA, patchy FZDZ
has occurred overnight ahead of an exiting shortwave. Wind field
across the northern Plains and Upper Midwest has begun responding to
the deepening surface low in southern Alberta, becoming
southwesterly, advecting in warmer air, as evidenced by slowly
rising temperatures overnight.

This afternoon into tonight, surface cyclone deepens as it races
southeast toward our CWA which looks to become under the left exit
region of the upper jet. Low level wind fields ramp up in response,
with warm advection continuing. As the upper wave approaches,
widespread precip will develop.

North of I-94, confidence is high that precip will fall as all snow
around 5 to 10 PM this evening with snow rates above 1" per hour
expected given strong forcing from the upper wave and an axis of
700/850mb frontogenesis developing on the northern periphery of the
warm advection. While totals may not quite reach 6" (only about a
30% chance per 09.00z LREF/HREF/NBM), expected impacts from the high
snow rate are sufficient to continue the Winter Storm Warning.

For areas south/west of I-94, progged soundings suggest warm
advection will have been sufficient enough for a warm nose to
develop, leading to a period of freezing rain. While this freezing
rain should end after a couple of hours as surface temperatures
continue to climb, cold pavement temps and widespread snow cover may
lead to additional droplets continuing to freeze even as 2m
temperatures reach above freezing. Thus, a light glaze of ice to a
few hundreths in accumulation is expected. Have therefore expanded
the ongoing Winter Weather Advisory to cover the remainder of the
CWA.

For areas right along I-94, uncertainty in the exact source of
impacts - snow and/or freezing rain - remains stubbornly high.
Global models, as evidenced by the 09.00z LREF, are a bit farther
south with their axis of high probability to reach 3" of snow
compared to high resolution ensembles, as evidenced by the 09.00z
HREF and particularly the 09.00z REFS. For example, 09.00z LREF
shades potential for 3" of snow close to La Crosse while the HREF
keeps 60% probabilities close to I-94. Overall run to run trend in
LREF has been toward the north, however, so continue to think cutoff
of appreciable snow impacts will reside around or just south/west of
I-94. As for ice, areas along I-94 are favored to only receive a
light glaze as warm advection looks to end before an appreciable
warm nose develops.

Moving ahead to the overnight hours, 09.00z NAM/RAP soundings
suggest the presence of strong near surface lapse rates with
saturation at the top of this conditionally unstable boundary layer
immediately following the passage of the surface cold front.
Therefore, there will be potential for a short burst of intense snow
showers following the passage of the cold front. Progged low level
lapse rates are steepest in areas west of the Mississippi, so will
need to watch this area closest.

Finally, surface winds will be on the increase overnight outside of
the aforementioned snow showers as a 55 knot 850mb jet overspreads
NE IA, far SW WI, and parts of SE MN in the presence of strong CAA
aloft. 09.00z HREF wind probabilities suggest a 50 percent chance
for winds to top 30 mph with a 70% chance for 45+ mph gusts. While
the gust probabilities may be inflated due to the presence of the ARW
in this ensemble, this suggests close consideration will be needed
for a Wind Advisory overnight into Wednesday morning. Surface snow
conditions will also need to be monitored - while the period of
freezing rain and rain described in NE IA and SE MN described above
should lead to a crust developing on the surface of the snow pack,
if the top of the snow pack remains susceptible to blowing, very low
visibilities could result and a pivot toward blizzard headlines
would need to be considered.

Very cold Saturday and Sunday

After another upper trough swing southeastward over the Great Lakes,
an even colder air mass invades the region. Lows Saturday and Sunday
mornings are favored to be below zero with wind chills of -25 or
lower possible. Will focus on the details of this upcoming cold snap
in the coming days.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1139 AM CST Tue Dec 9 2025

Messy aviation forecast over the next 12-24 hours is shaping up
across the Upper Mississippi Valley. A deck of LIFR to MVFR
stratus is currently situated over the area with a few breaks
to allow for transient VFR conditions at times. Precipitation
begins to move in later this afternoon from the northwest.
Precipitation will likely start in the form of snow and freezing
rain with a transition to rain/snow this evening. As cold air
begins to move in on the back side of this system, precipitation
will change over the snow overnight. CIGs and visibilities will
likely remain in the MVFR to low end-IFR range (some high-end
LIFR possible) for much of the period with slight improvement
expected after 12Z. Winds are expected to pick up quite a bit
overnight with some blowing snow potential, especially for areas
along and west of the Mississippi (including the RST terminal).
Wind gusts for the overnight time period will be in the 35-45
kt range west of the river with 25-35 kt gusts possible along
and east of the river. Southerly winds at the start of the
period will gradually veer to the west/northwest this evening
and into the overnight period with speeds on the rise starting
later this afternoon.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST
     Wednesday for WIZ032>034-041>044-053>055-061.
     Winter Storm Warning from 3 PM this afternoon to 6 AM CST
     Wednesday for WIZ017-029.
MN...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST
     Wednesday for MNZ079-086>088-094>096.
IA...Winter Weather Advisory from 3 PM this afternoon to 6 AM CST
     Wednesday for IAZ008>011-018-019-029-030.

&&

$$

DISCUSSION...Ferguson
AVIATION...Barendse