685
FXUS63 KARX 072350
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
550 PM CST Fri Feb 7 2025

.KEY MESSAGES...

- Winter Weather Advisory for snow tonight into Saturday
  afternoon for most along and north of I-90. Highest
  accumulations north of I-94 where 3-6" are forecast with
  locally higher amounts possible. A sharp gradient in amounts
  further south with 1-4" forecast along and between I-90 and
  I-94.

- Cold temperatures return for next week with morning wind
  chills as low as -5 to -20 degrees.

- Snow shower chances (20-50%) for Monday evening and overnight,
  little to no accumulations are currently expected.

&&

.DISCUSSION...
Issued at 238 PM CST Fri Feb 7 2025

Tonight into Saturday: Accumulating Snow

Expected snowfall amounts over the last 24 hours have changed
notably. Yesterday`s forecast at this time showed a 60 to 80% chance
of 4+ inches of snow along the I-90 corridor from Rochester through
La Crosse to Tomah. Those chances decreased to around 40 to 50%
overnight and then to around 20% this afternoon as higher-resolution
models have been taken into account. Along and north of I-94,
expected snowfall totals remain similar as before. With the
inclusion of higher-resolution models, we are monitoring the
potential for locally higher amounts due to a frontogenetic band
across portions of central Wisconsin. Opted to transition the Winter
Storm Watch to a Winter Weather Advisory after collaboration with
neighboring offices due to lower confidence on where this band of
higher snowfall amounts is expected. It is possible that we upgrade
Clark or Taylor county to a Winter Storm Warning tonight if
confidence in the snowband location increases.

Snow to liquid ratios are expected to be around 16-17:1, with
locally higher ratios within any potential fgen band. There are some
model differences on what level the fgen band takes place in
relation to the DGZ. Some models have the best forcing for ascent
above the DGZ, which would produce lower snowfall amounts than if
the lift was embedded within the DGZ.

Another potential scenario is the chance for freezing drizzle
Saturday morning across portions of NE Iowa and south of the
Wisconsin River in Grant County. Model soundings suggest saturation
and lift through roughly 700mb withe the thermal profile just
grazing the DGZ. Confidence is too low at this time for any
potential headlines, however recent modeled guidance suggests any
ice accumulation would be on the lighter side - still enough to
create slippery conditions on untreated surfaces.

Sunday - Thursday: Trending Cooler With Some Precipitation Chances

As we head into next week, high pressure will dominate much of
pattern for the middle of the week after a cold frontal passage on
Monday. Additionally, with zonal to weak northwesterly flow, a
colder airmass will sink down into the region for Tuesday through
Thursday. 850mb temperatures in the 07.12z GFS fall to -17 to -20C
with median morning low temperatures in the recent grand ensemble
(GEFS/EC ensemble/Canadian ensemble) in the single digits above and
below zero. However, considering the snowpack in portions of north-
central WI, temperatures would likely trend lower into the teens
below zero for morning low temperatures. In addition,
probabilities for wind chills of 20 below or colder remain
fairly respectable (20-60%) in the grand ensemble (GEFS/EC
ensemble/Canadian ensemble) as well. Again with the more present
snowpack in north-central WI this could push aid in pushing
wind chills cooler with some probabilities (20-40%) for wind
chills of 25 below zero or colder.

As far as precipitation chances are concerned, a cold front passes
through the area on Monday which an accompanying band of low-level
frontogenesis shown in the 07.12z NAM. As a result, the NAM shows an
area of snow shower development in portions of southern MN that
progresses southeast throughout the evening. However, with the grand
ensemble (GEFS/EC/Canadian ensemble) showing lower probabilities (10-
30%) for 0.5", would not expect much for any accumulations at this
time. Otherwise, with the fairly progressive upper-level pattern, a
secondary upper-level trough will amplify across the central CONUS
Wednesday and into Thursday. However, much of deterministic guidance
keeps any associated precipitation further south of the region. As a
result, have held with the precipitation chances within the national
blend for now.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 550 PM CST Fri Feb 7 2025

VFR conditions continue into the overnight hours. MVFR ceilings
begin to move in from west to east late tonight and into
Saturday morning, generally around 2-3kft. There is a band of
snow moving eastward across central Minnesota currently, and
would reduce visibilities in north-central Wisconsin if it
holds together.

The main round of snow moves in Saturday morning, moving west to
east with time. Lower ceilings, MVFR to possibly IFR in some
areas, as well as MVFR to IFR visibilities are expected as the
snow moves into the area. The heaviest snowfall is expected
along and north of I90, especially north of I94, but snowfall
is possible across the entire area (40-90%). Lower
ceilings/visibilities will be associated with areas of heavier
snowfall. Winds will be variable overnight, but generally shift
counter-clockwise from the southeast to the northwest through
the TAF period.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 4 AM to 6 PM CST Saturday for
     WIZ032>034.
     Winter Weather Advisory from midnight tonight to 6 PM CST
     Saturday for WIZ017-029.
     Winter Weather Advisory from 9 AM to 6 PM CST Saturday for
     WIZ043-044.
MN...Winter Weather Advisory from 4 AM to 6 PM CST Saturday for
     MNZ079-086-087.
IA...None.

&&

$$

DISCUSSION...Naylor/JAW
AVIATION...Falkinham