729
FXUS63 KARX 292358
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
658 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- Fog potential increasing for tonight, with visibilities low
  enough to impact travel most likely along and north of
  Interstate 94. These impacts may expand southward and trends
  need to be monitored.

- Mostly dry conditions for Labor Day Weekend with low chances
  (10 to 30%) for showers and storms each afternoon. By midweek
  a better chance (25 to 50%) for more widespread showers and
  storms.

- Near-normal temperatures through Tuesday then below normal
  temperatures for midweek.

&&

.UPDATE...
Issued at 655 PM CDT Fri Aug 29 2025

It has been a challenging evening forecast given the influence
of the dense stratus that failed to clear out over west-central
Wisconsin today and is actually starting to expand
southwestward. This plays into the fog potential for later
tonight. Daytime high temperatures struggled to reach the
mid-60s over the bogs of western Wisconsin this afternoon,
resulting in RH values at 6:30pm already near 100 percent from
the Eau Claire to Black River Falls to Wisconsin Dells corridor.

A stratus deck continues to hold fast in these areas but is
clearing from the north with an influx of drier northerly air.
An extrapolation of this clearing has it reaching the I-94
corridor between 06-09Z, at which dense fog is most likely to
develop and then linger into the mid-morning. Further south and
west, confidence in the development and thickness of fog is far
less certain as the stratus has begun expanding westward and may
encompass much of the region by sunrise. Exactly how far west
the stratus advances is a wild card and will play into the fog
coverage and intensity in these locales.

May need to explore issuing a dense fog advisory for areas at
least along and north of I-94 later this evening if trends
continue, with the western and southern extents of the advisory
driven by immediate visibility trends.

&&

.DISCUSSION...
Issued at 137 PM CDT Fri Aug 29 2025

Today-Tuesday: Scattered Showers and Storms Today then Low Rain
Chances into midweek, Seasonable Temperatures

A shortwave trough continues to make its way through the Upper
Midwest bringing a small complex of showers and storms with more
scattered showers and storms behind it. This complex will move out
of the CWA early this afternoon. After this moves out, a narrow band
of scattered showers and storms lingers through the evening. All
rain chances diminish by midnight. While the complex of rain will
mostly be rain showers, instability builds in this afternoon with
values of 400 to 750 J/kg of MLCAPE. The shear will also be quite
weak as the better shear remains displaced from the convection. As a
result, no organized convection is expected and while a stronger
storm can not be ruled, severe weather is not expected. One thing to
add for the scattered showers and storms for this afternoon, they
will form along a weak surface boundary and as we had a couple
reports of funnel clouds in northeast Iowa from this same boundary,
this afternoon could be a similar story for southeast Minnesota and
northeast Iowa as the RAP non-supercell tornado parameter is
highlighting this same area again as with this weak boundary there
will be some surface vorticity to work with and increasing
instability to potentially lead to the formation of funnel clouds.

Heading into Labor Day weekend, a shortwave undercuts a ridge
located in southern Canada. This will bring increased chances of
rain for portions of the Central Plains and Upper Midwest. The best
precipitation chances remain west of I-35 while only a 10 to 30%
chance for showers and storms exists for portions of southeast
Minnesota and northeast Iowa during the afternoons on Saturday
through Monday. By Tuesday there is a little shortwave energy that
comes down from an approaching longwave trough. This will increase
shower and thunderstorm chances once again for Tuesday afternoon and
evening. Temperatures through Tuesday remain a few degrees below
normal with highs in the mid to upper 70s.

Midweek: Cooler and More Rain Chances

Guidance continues to be in agreement that a deep longwave trough
dips down into the Upper Midwest and Great Lakes regions. While this
trough will bring more chances of rain, the bigger story is the
potential for much cooler weather. The Grand Ensemble
(EPS/GEFS/CMCE) continues to show 850mb temperatures ranging from 3
to 7C for Wednesday into Thursday, with single digit 850mb
temperatures (Celsius) remaining through Saturday. EFI values for
Thursday are already between -0.8 and -0.9 indicating that
temperatures are on the lower side of the climatological normal.
Current NBM forecasted high temperatures for Thursday are in the
upper 50s to low 60s while the overnight lows are forecasted to be
in the upper 30s to mid 40s. While these are the forecasted
temperatures from the NBM, there is still some uncertainty of how
deep the trough gets. The deterministic ECMWF has a cooler and
deeper trough than the GFS. while this remains an area of
uncertainty, ensemble guidance continues to support below normal
temperatures from midweek through the end of the week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 655 PM CDT Fri Aug 29 2025

Widespread IFR to LIFR restrictions expand in coverage
overnight owing to either low stratus or fog developing, with
the fog lifting by 14Z and the stratus lifting/scattering out
from north to south during the late morning to mid-afternoon.
Winds will be light from the east around 5 kts.

&&

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

&&

$$

UPDATE...Skow
DISCUSSION...Cecava
AVIATION...Skow