448
FXUS63 KARX 310801
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
200 AM CST Fri Jan 31 2025

.KEY MESSAGES...

- Snow north of I-94 Sat afternoon/night with 1 to 3" currently
expected. Snow to a wintry mix possible south of there with
generally minimal accumulation.

- Mild through the weekend and could flirt with 50 degrees
along/south of I-90 Sunday. Colder, but more seasonable for the new
work week.

&&

.DISCUSSION...
Issued at 200 AM CST Fri Jan 31 2025

BOTTOM-LINE UPFRONT: confidence high for snow north of I-94 Sat
afternoon/night. Accums currently progged from 1 to 3". Some
potential for winter wx headlines. South of there a blend of snow to
wintry mix to drizzle all possible - and confidence much lower in
how that plays out.


WEEKEND: accumulating snow chiefly north of I-94 Sat, smattering of
pcpn chances and ptypes elsewhere. Staying mild - but not nearly as
warm as Thursday.

A mish-mash of forcing mechanisms for the weekend: elongated bits of
shortwave energy sprinting west-east in the quick moving upper level
flow, QG convergence through the layers, Fgen sfc/aloft with various
boundaries, strong low level thermodynamics (at times), etc. The key
is how much saturation, where and when, will this forcing have to
work on?

And that is the challenge to this forecast - how the saturation
profile will look...ice in the cloud, deep enough to foster pcpn
production, seeder-feeder process, etc. Looking at forecast
soundings and time/height x-sections, saturation is on the increase
from the west across northern parts of the region Sat, deeper north
of I-94. South of there, some mixed signals in the models on whether
an increase in the near sfc moisture would start of if its mainly a
mid deck of clouds. Implications on pcpn chances as strong low level
thermodynamics are kicking in by then. Moving into Saturday night,
the deeper saturation continues to the north but could/would spread
southward. Medium range guidance then suggests there could be a
shallowing of the layer from top down - enough to lose ice in the
cloud for late evening/overnight. How much forcing is available for
pcpn production is debatable, moreso south of I-90.

Again, it`s a messy scenario with a lot of moving parts. At this
time, confidence remains highest on the likelihood of snow along and
north of I-94 for Sat afternoon through the night. Latest Grand
Ensemble run paints 60-80% chances for 1+" in this area, with a 10
to 40% for 3+" (the higher chcs lie north of hwy 10 in WI).

Moving south of there the confidence drops off with how pcpn types
will manifest. Current favored scenario suggest snow would be the
main ptype for Sat afternoon, but transition to drizzle (freezing
drizzle?) moving into the evening/overnight. Temps currently progged
to hold above freezing, but awfully close. That said, The NBM holds
with mostly snow for Sat night. Will opt to stick with this for now.
Again, confidence in how the moisture profile in the vertical will
flesh out is low.

After this first push of pcpn chances exits east Sun morning another
ripple in the upper level flow is slated to track east across
northern parts of the region Sunday aft/evening (farther north than
the first system). Chiefly snow chances would result - north of I-94
for now. Any additional accumulation looks minimal.

For temps - 10 to 15 degrees cooler today, but still well above
normal. Saturday will be tempered even more by clouds/pcpn. Bump in
the low level temperature profile/warm air advection for Sunday and
50 could again be reached along/south of I-90.


NEXT WEEK: the long range guidance continues to hold onto quick
moving, quasi-zonal flow a loft. The stronger ridging that brought
the warmth of the past several days (and this weekend) flattens,
replaced by periods of troughing and lesser amplitude ridging. Temps
will drop back to more seasonable levels - colder than normal at
times. The GEFS and EPS still showing some differences in how
quickly these ridge-trough periods switch out. However, they are
both adamant that the flow will usher in various bits of shortwave
energy, some elongated and/or in series. Period of pcpn (more likely
snow given the colder temps) will result. Questions on
timing/location though. Will continue to ride the model blend for
temps/pcpn chances for the new work week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 940 PM CST Thu Jan 30 2025

IFR to LIFR ceilings/visibilities move as far north as an HPT
to LNR line after 06Z before sinking back to the south around
12Z. VFR conditions are forecast for the remainder of the
period. Winds will be from the north around 5-10 kts through the
day, gusting up to 15-20 kts from midday to mid-afternoon.
Winds back more to the east after sunset.

&&

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

&&

$$

DISCUSSION...Rieck
AVIATION.....Skow