439
FXUS63 KARX 222339
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
539 PM CST Sat Feb 22 2025

.KEY MESSAGES...

- Intermittent light precipitation chances (20-50%) throughout
  next week. While rain will be the more common precipitation
  type early in the week, some snow may mix in at times.

- Seasonably mild temperatures throughout much of the upcoming
  week with highs in the upper 30s to 40s areawide.

&&

.DISCUSSION...
Issued at 217 PM CST Sat Feb 22 2025

Overview:

The latest water vapor satellite imagery and 500mb heights showed
northwest flow aloft across the northwest quarter of the u>S with a
500mb trough embedded in the flow across the Ohio River Valley and
another area of troughing over TX/NM.  A weak shortwave trough was
located over MT/WY.  Weak embedded shortwave trough energy moving
through norther MN and northern WI were producing some patchy light
snow.  At 19Z, skies were clear to partly sunny with increasing mid
and high level cloudiness across parts of MN.  Temperatures were in
the 20s to around 30 degrees with southwest winds mostly 5 to 15 mph.

Tonight and Sunday:

An embedded shortwave is forecast to move across the Dakotas tonight
and into the Upper Mississippi Valley Sunday.  Forecast soundings
show increasing moisture above 10kft tonight with some lower
ceilings 5-10kft Sunday with dry air below.  The main forecast
problems for tonight into Sunday are the low temperatures tonight,
maximum temperatures for Sunday, and if/where flurries can reach the
ground.  The rise in temperatures continued today with highs in the
20s to lower 30s, but temperatures have been slow to warm. We still
have 1 to 6+ inches of snow across the forecast area and are looking
for clouds to move in for Sunday. Between tonight and Sunday
afternoon, we see westerly flow continue with a 3 deg warm up in our
850mb temperatures. Temperatures are forecast to remain about 10
degrees warmer tonight in the teens. Did back off on the highs for
Sunday and went more with our 50th percentile of NBM which has highs
in the 30s and spotty 40s where snow cover is lacking. The HREF has
some small chances for flurries 0 to 10% . Forecast soundings are a
bit dry below 5-kft. Due to the lower confidence/dry air, did not
include flurries south of I94, but did mention north of I94 for a
few hours in the morning.

Monday - Tuesday: Mild with Some Precipitation Chances

As we start the work week, some upper-level ridging ahead of an
incoming shortwave trough will instigate some warming with 850mb
temperatures in the 22.12z GFS/EC warming to around 6-8C. As a
result, the recent grand ensemble (GEFS/EC/Canadian ensemble)
has median high temperatures in the 40s areawide. Some members
would suggest river valley locations may top 50 degrees in some
spots, however with the snow cover likely still in place would
think this is more unlikely. Certainly quite the warm up though
from where we have been over the past week! These milder
temperatures will likely persist into Tuesday, but maybe ever so
slightly cooler with some cooling in 850mb temperatures to
around 2-4 C. Regardless, median temperatures in the grand
ensemble for Tuesday and through much of the work week for that
matter remain in the 40s.

As far as precipitation chances go for Monday night, the
aforementioned shortwave trough moves into the local area and
increases our precipitation chances (15-30%) during the late evening
on Monday. Based on the 22.12z NAM soundings, thinking that in most
spots rain will be the predominant precipitation type as the near-
surface freezing layer keeps between 2-3kft which should keep
hydrometeors in the liquid variety at the surface. However, would
not rule out some spots where snow mixes in on ridgetops or
typically colder spots in north-central Wisconsin as complete
saturation into the dendritic growth zone is present along with a
slightly shallower surface warm layer. Regardless, ensemble guidance
does not paint much for QPF with this system as the current grand
ensemble (GEFS/EC/Canadian ensemble) has medium probabilities (40-
60%) for even seeing measurable precipitation and low probabilities
(10-30%) for seeing 0.1" of QPF with this Monday night wave.

Wednesday - Friday: Remaining Seasonably Mild With Additional
Precipitation Chances

Looking towards the pre-dawn hours Wednesday morning, a secondary
shortwave trough will move through the region in northwesterly flow
yet again increasing our precipitation chances (20-40%) across the
area. Overall looks to be yet again a predominantly rain p-type with
an above freezing surface layer to around 2-3kft for most of the
area. However, this lowers a bit across portions of north-central
Wisconsin where some snow may yet again mix in but with no
accumulations currently expected. With this Wednesday system, the
QPF story is fairly similar with decent probabilities (50-70%) for
measurable precipitation in the grand ensemble but low probabilities
(10-30%) for amounts over 0.1" through Wednesday afternoon.

Thursday features another quick lobe of shortwave energy that swings
down into the area within the northwesterly flow. Would expect some
residual cloud cover with maybe a couple isolated showers for the
local area with diurnal mixing, some very minimal instability (under
10 J/kg) in spots and low-level saturation shown in the 22.12z GFS
soundings. The question would really be if the saturation is deep
enough in conjunction with the wave to support any precipitation
production. As a result, decided to hold with the no precipitation
mention in the NBM for now due to the lower confidence.
Additionally, thinking that temperatures for Thursday could be
marginally cooler with some cloud cover overhead for peak heating
hours. However, very likely would remain milder than normal with
highs still in the 40s for most.

Upper-level ridging briefly returns for Friday ahead of a more
robust upper-level trough and corresponding developing surface low
that swings out of western Ontario by Friday night. At this point
there appears to be a bit more spread in ensemble guidance on the
timing of a cold frontal passage going into the weekend with the
10th to 90th spread of high temperatures in the 22.13z NBM at La
Crosse being anywhere from 33 to 61 degrees for Friday and similar
larger spread in the grand ensemble as well. Looks like decent
probabilities (40-70%) in the grand ensemble for some measurable
precipitation during this period, however this will likely be
contingent on how much moisture this system has access to which
currently appears to be minimal. As a result, probabilities for
amounts of 0.1" or greater in the grand ensemble are low
(10-20%).

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 535 PM CST Sat Feb 22 2025

VFR conditions are forecast for the TAF period with light
southwest winds of 5-10 kts. Looking ahead to Sunday night and
Monday morning, there is a 30-50% chance of seeing at least MVFR
visibilities due to fog west of the Mississippi River, but
confidence is low on the degree of aviation restrictions.

&&

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

&&

$$

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