211
FXUS63 KARX 052357
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
557 PM CST Wed Feb 5 2025

.KEY MESSAGES...

- Wintry precipitation likely (50 to 90%) this afternoon through
  tonight. Accumulating snow for areas mostly along and north of
  I-90 with highest accumulations in north-central Wisconsin
  where 1 to 2 inches is forecast. A glaze of ice is possible
  along and south of I-90 with the best chance in portions of
  northeast Iowa and far southwestern Wisconsin (40 to 60%).

- Strong winds expected Thursday afternoon and evening.
  Sustained winds of 20-30 mph and wind gusts of 35-50 mph
  possible. Wind Advisory likely.

- Accumulating snow likely Friday night into Saturday night.
  Some areas could potentially see greater than 6 inches along
  and north of I-94. However, this depends on the track of the
  system. Details subject to change over the coming days.

&&

.DISCUSSION...
Issued at 226 PM CST Wed Feb 5 2025

This Afternoon Through Tonight: Light Wintry Precip Expected

A shortwave trough is currently moving through the Northern Plains
and is progged to move through our area later today and into the
overnight hours. As of 1:45 PM, we currently have a broad swath of
elevated snow showers moving east northeast across the area. None of
this looks to be reaching the ground as we are still dealing with a
very dry sub-cloud base, generally between 750-900 mb. Until we can
get this to saturate, which doesn`t look to happen until late this
afternoon into this evening according to 05.12 HREF soundings
(generally after 23Z), we don`t expect to see much in the way of
precipitation. We have generally lowered PoPs for this time frame
across the board with a gradual ramp up into this evening and
overnight tonight. The initial precip type looks to be light snow
with an elevated DGZ and ice in the upper levels. However, upper
level ice becomes less likely after 00-03Z. A warm nose in the
lower to mid levels, which seems to be a bit under-done in some
hi-res model soundings, will eventually help to melt some of
these ice crystals into super-cooled drops. Since we likely
won`t get cold enough (surface temperatures in the teens to
lower 20s) to completely refreeze into snow, freezing drizzle
looks to be the dominant precipitation type through much of the
overnight hours. Current observations downstream in Iowa confirm
that freezing drizzle seems to be the dominant precipitation
type and we expect this trend to continue. As you move north,
the warm nose seems to fall off with the dominant precipitation
type looking to stay as snow. That being said, significant snow
totals have been shifted north with the latest trends. Totals
have been capped at around 2 inches with most places likely only
seeing a trace to maybe an inch in the Chimney. Ice
accumulations across the area are generally capped to 0.03
inches with most places likely only seeing a light glaze. As an
occluded front moves through late overnight, this will shift
winds to the west/northwest which will significantly dry out the
layer, cutting off precipitation chances between 06-12Z. The
morning commute Thursday morning may be a bit slick, especially
on any untreated roads but significant icing is not expected.

Winds for Thursday afternoon and night

A subtle shortwave trough will move southeast through the area on
Thursday afternoon. In its wake, the pressure gradient will tighten
and the the 950-850 mb lapse rates will steepen. This will result in
the sustained winds will climb into the 20 to 30 mph range. BUFKIT
soundings show that the wind gusts in the mixed-layer will be mainly
in the 35 to 50 mph range. There may be a few higher gusts in the 50
to 55 mph range, but these probabilities look low (mainly up to 20
percent in the HREF and NBM). The strongest wind gusts will be
during the afternoon and evening. At this time, it looks like a Wind
Advisory will be likely needed for this time period. As far as when
would this be issued, thinking that this would be later tonight or
on Thursday morning.

Late Friday night through Saturday Evening

The models continue to show that the area will be likely affected by
a system in the northern and southern stream. As these systems move
east of the area, the models continue to show that these two systems
will likely phase. This results in an inverted trough or deformation
band snow moving east and southeast across the area. However, there
is plenty of uncertainty on where this will ultimately occur. In the
05.12z models, there was a shift south by 1 to 2 counties.

In addition to the placement of the inverted trough or deformation
band, there is also uncertainty on the snow to liquid ratios. This
is due to the likelihood for frontogenetic banding and where there
may be a deep layer (200-300 mb) of temperature profile in the
dendritic growth zone.

Looking at the LREF and NBM 10th-90th percentiles for snowfall,
there is a 3 to 5 inch spread in the models south of the Interstate
90 corridor and up to 5 inches across the remainder of the area. The
highest snowfall totals continue to be along and north of the
Interstate 94 corridor.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 553 PM CST Wed Feb 5 2025

Light snow and freezing drizzle remain the primary concerns this
evening as we head into the overnight hours. Expecting light
snow north of I-94 and freezing drizzle south of there. As such,
have opted to remove the mention of snow from the TAF sites.
Thinking wintry precipitation should start within the next hour
or two across the area, continuing into the overnight hours
before ending west to east Thursday morning.

Primarily MVFR conditions are expected overnight, but IFR
ceilings are possible along and south of I-90 overnight as the
drizzle continues moving northward, with the NBM beginning to
suggest higher probabilities of this occurrence (30-50%).
IFR/MVFR ceilings dissipate Thursday morning. Otherwise, winds
will turn to a westerly direction Thursday. Strong gusts of
25-35KT are possible across the area beginning Thursday morning,
continuing throughout the afternoon. Winds may allow for
blowing snow in north-central Wisconsin tomorrow, which would
lower visibilities across this region.

&&

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

&&

$$

DISCUSSION...Barendse/Boyne
AVIATION...Falkinham