670
FXUS63 KARX 222058
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
258 PM CST Wed Jan 22 2025

.KEY MESSAGES...

- Off and on flurries/snow showers will continue into the
  overnight hours. Minimal additional accumulations are
  expected, however visibilities could be reduced for a time
  with the cold front medium probabilities ((30-60%) for
  visibilities under 1 mile this evening.


- Temperatures fluctuate over the next few days with highs in
  the teens for Thursday and moderating into the 20s and 30s to
  start the weekend (60 to 100% probability that temperatures
  remain below 30 deg F through Friday).

- Light snow showers again possible Friday through Saturday
  night, 40 to 80% for measurable (0.1" or more) with higher
  probabilities north of I94.

&&

.DISCUSSION...
Issued at 242 PM CST Wed Jan 22 2025

Rest of Today - Tonight: Scattered Flurries and Snow Showers:

Current water vapor imagery and 22.18z RAP 500mb heights depict a
shortwave trough with a cold frontal boundary across north-central
Minnesota. Further southwest, a secondary wave and vorticity lobe is
aiding the instigation of precipitation across southern portions of
the area in southwestern WI and northeast IA. As this wave continues
to pivot east, thinking this initial axis of precipitation will
slowly shift east of the local area over the rest of the afternoon
and into the evening. Attention then turns towards the
aforementioned cold front as it sweeps through the area this
evening. Fairly solid agreement amongst the CAMs that low-level
frontogenesis and steeper 0-2km lapse rates will instigate a broken
line of snow showers. While minimal accumulations are anticipated
with these, brief visibility reductions to a mile or lower may be
possible as indicated in the 22.12z HREF with medium probabilities
(30-60%) for visibilities under 1 mile this evening with some
increase in wind gusts to 20-30 mph behind the front. Given their
remains some steeper low-level lapse rates into the overnight hours
in the recent RAP/HRRR, held onto some flurries through midnight
where this environment is more favorable east of the Mississippi
River.

Tomorrow: Briefly Cooling Down:

As we head towards sunrise tomorrow, the aforementioned trough axis
moves overhead with 850mb temperatures of -17C to -19C overhead in
the 22.15z RAP. As a result, guidance continues to reflect overnight
lows falling below normal with the median low temperatures in the
national blend in the single digits, perhaps some areas below zero
in southeast MN and north-central WI with lingering cloud cover
posing some questions as to how far we will drop. With some breezy
winds still in place behind the front, wind chills will bottom out
in the teens to around 20 below zero overnight, outside of advisory
criteria but will still feel unpleasant. As high pressure moves into
the region for late morning and afternoon, expecting clouds to
diminish albeit still remaining colder than normal with highs
generally in the upper single digits to teens for the afternoon on
Thursday.

Below normal through Friday with moderation into the weekend.  Light
snow showers possible for parts of the area Friday through
Saturday night:

Thursday night, a large area of cold high pressure is forecast to be
over the region with -20 deg C 850mb isotherm stretching from the
U.P. of Michigan into Ontario and Quebec Canada. The thermal trough
shifts to the east with light northwest surface flow becoming
southwest, then westerly into Saturday.  Some moderation in
temperatures is forecast for Friday, however the westerly winds
Saturday should boost readings to above normal levels for the
weekend. Normals are still in the 20s for highs and single digits
for lows.

Once again, a broad trough aloft with drag a cold front through
the area. Depending on the thermal/moisture/lift fields, some
light snow may try to develop over parts of the forecast area
Friday afternoon into Friday and then with the cold front later
Saturday afternoon into Saturday night. The organized light snow
is currently forecast north of the forecast area, however with
the push warm air advection followed by the cold air, some
flurries or snow showers could extend southwestward into the
forecast area. We have added snow chances to this period,
however as we refine the timing, the POPs will likely increase.
Relatively warmer air is already moving in Saturday night and
Sunday, thus seasonable temperatures are forecast. We`ll need to
monitor this wave as the 22.12Z NAM snow squall parameter was
highlighting some steep lapse rates over the area with low
values of CAPE Saturday afternoon.

Although the broad trough over Canada expand Sunday into Monday, we
are far enough to the west where a more westerly/relatively milder
airflow is expected and the storm track remains over the Upper
Great Lakes region. Above normal highs in the 20s and 30s for
Monday and Tuesday continue to warm with 30s to around 40
possible for Wednesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1150 AM CST Wed Jan 22 2025

MVFR cigs and snow showers will be the primary aviation concerns
through the TAF period. Currently, low-VFR stratus prevails across
much of the area with low-level saturation in place. Weak pieces of
lift show in the CAMs continue to propagate snow shower
activity, with a band of light snow located near I-90 from just
east of Rochester and into La Crosse. As we head through the
afternoon, a brief lull in snow shower activity is expected
before a cold front approaches the area switching winds to
northwesterly and increasing them to around 10-15 kts. As the
front moves through the area, snow shower chances (20-40%)
return east of the Mississippi River this evening. As a result,
have included a prob30 group at KLSE to cover this potential.
With the passage of the front low-stratus will note a slight
reduction in cigs to MVFR levels with little improvement noted
in guidance until around 18z.

&&

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

&&

$$

DISCUSSION...Naylor/Zapotocny
AVIATION...Naylor