797
FXUS63 KARX 051748
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1148 AM 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 3 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%).

- Snow chances return Saturday (80 to 100%). Probabilities for
  at least 1 inch of snow are 50 to 90% with higher
  probabilities along and north of I-90. There is also a low
  signal (20 to 40%) for at least 4 inches to occur along and
  north of I-90. Details on this storm will be better as the
  weekend gets closer.

- Colder air returns early next week with wind chills mainly
  between -5 and -15 degrees.

&&

.DISCUSSION...
Issued at 405 AM CST Wed Feb 5 2025

Today-Thursday: Wintry Mix Precipitation for Today, Gusty Winds
Thursday:

Weak shortwave ridging continues to be in place over the area.
During the afternoon, a shortwave trough will move into the region
and bring a wintry mix of precipitation to the Upper Midwest. This
will shift winds to the southeast and eventually the southwest. Warm
air advection in the low levels, ~925mb, will help to warm
temperatures above freezing at this level while surface temperatures
remain at or below freezing. Initially a dry sub cloud layer will
exist, however as this warm air advection and moisture advection
kicks in during the afternoon and evening, the low levels should
saturate and precipitation will then form. The first precipitation
type is expected to be snow, however as ice is removed from the
upper levels, snow will become less likely. The previously mentioned
warm nose of air around 925mb will help to melt any frozen
precipitation and turn it into a liquid. Due to the surface
temperatures being in the upper 20s to near freezing for most areas
south of I-94 in the afternoon and evening, these liquid particles
are not expected to refreeze. With no ice present aloft, a good warm
nose at the low levels, and low level lift, freezing drizzle is
expected to mix in with light snow. The further north you go towards
I-90, the warm nose looks less impressive and light snow may be the
dominant precipitation type. The best area for freezing drizzle to
occur and potentially be the dominant precipitation type is portions
of northeast Iowa and far southwestern Wisconsin. This is also shown
in the NBM probabilities where a 40 to 60% chance for a glaze of ice
is possible for portions of northeast Iowa and far southwestern
Wisconsin. Outside of this area, where the warm nose looks less
impressive, along and south of I-90, the probabilities of a glaze of
ice are much less, 10 to 30%. The main ingredient of this storm
system that will impact the precipitation type is how strong the
warm nose actually is. If it is stronger than freezing drizzle will
be more likely to occur and the droplets could reach the surface. If
it is cooler, than a light snow would likely occur instead.

For areas north of I-94, snow will be the dominant precipitation
type. Soundings in north-central Wisconsin are starting to show signs
of ice leaving the upper levels, which means there`s a chance (20 to
40%) where freezing drizzle could occur, especially in Clark and
Taylor counties. With the snow being the main precipitation type,
these two counties are expected to see 1 to 3 inches of snow with
the higher totals in Taylor county. Precipitation is expected to end
by sunrise for our northern counties, however the surface low
associated with the trough will pass our area to the north. As a
result, strong west to northwest winds will be present. Current
forecast has sustained winds of 15 to 20kts with gusts mostly
ranging from 30 to 35kts. This will play a role in north central
Wisconsin, where the most snow will fall. Due to the strong winds,
blowing snow will be possible in this area during the morning and
afternoon. The gusty winds will subside during the evening as the
low gets further way from the area.

Friday-Weekend: Next System Looks to Bring Snow for Most:

Shortwave ridging moves into the region following the storm on
Wednesday to give way for a dry Friday. High temperatures are
generally forecasted to be in the upper teens to upper 20s. Heading
into Saturday, all ensemble members support a wave moving across the
Intermountain West and into the Upper Midwest. This will help give
the area a chance at some precipitation. With the surface storm
system displaced from the upper-level system, our region is expected
to stay on the cool side and thus keep precipitation type as snow.
Surface temperatures are mostly in the 20s across the area. When
looking at soundings for the weekend, a couple things stand out when
comparing this storm to Wednesday`s storm. One item to suggest we
stay as all snow is that the mid to lower levels does not have a
strong warm nose to help warm and melt the ice particles from aloft.
Another item is that ice looks to be present throughout much of the
mid and upper levels. Both of these points aid in precipitation type
being all snow. Snow ratios continue to range from 15 to 18:1 for
most areas south of I-94 with a 18 to 20:1 snow ratio for areas
north of I-94. When looking at possible snow totals, the GEFS mean
continues to show lower probabilities compared to the GEPS/ENS
means. Another thing to note is compared to recent forecasts, the
LREF probabilities for greater than 4 inches has increased across
much of the area, with a general 20 to 40% chance along and north of
I-90 with the highest probabilities north of I-94. Similarly the
probabilities for greater than 1 inch of snow is roughly 50 to 90%
across the entire forecast area with the highest probabilities again
north of I-94. We will continue to monitor this trend, as well as
changes to the forecasted track of the storm system, and see if it
continues on with future forecasts as we get closer to the weekend.

Colder for Early Next Week:

The Upper Midwest remains in northwest flow aloft as we are on the
southern end of a longwave trough. Cold air will funnel southward
early next week lowering our highs to the teens to low 20s. Our low
temperatures are forecasted to be single digits above and below
zero. With some light wind present, the feels like temperatures are
expected to mostly range from -5 to -15 degrees with some areas
getting closer to -20 degrees.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1146 AM CST Wed Feb 5 2025

A small patch of MVFR CIGS are starting to erode across central
portions of the CWA with KRST back at SCT VFR. It may take
another hour for CIGS to erode back to VFR for LST so have
accounted for that in this package. Have also upped winds at
KRST and added gusts for portions of this afternoon.

The main story continues to be the chances for light snow and
freezing drizzle across the area this evening and into the overnight
hours. Both terminals will see CIGs drop to MVFR with some guidance
indicating a low (20%) chance of CIGs dropping to IFR. Have
added -FZDZSN to the prevailing groups as confidence remains
high that light wintry precipitation will be falling across the
area tonight as a system moves through. Precipitation chances
will gradually end from west/southwest to northeast late
overnight as a front moves through. This will also cause
south/southeasterly winds to veer to the west and become gusty,
especially by the early/mid morning hours. With the gusty winds,
areas that see more snowfall (Clark and Taylor counties) could
see some blowing snow which may impact visibilities through the
day tomorrow. MVFR CIGs look to scatter out by mid morning with
VFR conditions expected for most of the area.

&&

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

&&

$$

DISCUSSION...Cecava/Zapotocny
AVIATION...Barendse