715
FXUS63 KARX 220548
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1248 AM CDT Fri Aug 22 2025

.KEY MESSAGES...

- Quiet conditions are expected this afternoon and evening. Fog
  may develop again Friday morning, primarily in the fog prone
  valleys and across southwest Wisconsin.

- Showers and storms are possible Friday afternoon and overnight
  (20-40%). Some storms could possibly become strong, primarily
  in southeast Minnesota and north-central Wisconsin, but the
  overall severe threat is low.

- Below normal high temperatures are expected this weekend into
  early next week. Highs in the mid to upper 60s and lows in the
  mid 40s are expected. Some showers could develop Saturday and
  Sunday, primarily in north-central Wisconsin.

&&

.DISCUSSION...
Issued at 152 PM CDT Thu Aug 21 2025

This Afternoon and Friday Morning

With the dissipation of the fog this morning, diurnal cumulus
has developed across much of the region under high pressure and
mid to upper level ridging. Quiet conditions are expected into
the overnight hours with skies clearing as daytime heating
wanes.

Fog is on the docket again for Friday morning as high pressure
lingers across the Upper Midwest. Highest confidence in fog
formation is within the typical river valleys and southwest
Wisconsin where the lowest dewpoint depressions and lightest
winds are expected to coincide. The primary factor against fog
development is the introduction of high to mid cloud cover
associated with convection across northern Minnesota moving
southward into the region, which will likely hinder fog
development over southeast Minnesota into western Wisconsin. If
they`re able to move in early enough, these clouds could also
hinder development further southeast.

Showers and Storms Friday

500hPa longwave troughing noted over southern Canada this
afternoon continues to deepen and move eastward with time, which
will ultimately drag a cold front through the Upper Midwest
Friday night. Preceding the front, a surface trough is expected
to develop in association with weak mid-level shortwave energy
which may allow for some cloud and possibly shower/storm
development during the late morning to early afternoon. These
showers/storms could limit the instability that is able to
develop over our area through the remainder of the afternoon
ahead of the cold front. The primary instability axis during
this time is currently expected to build from southern Minnesota
into northern Wisconsin, with MLCAPE values of around 1000 J/kg
just nudging into southeast Minnesota (up to 1500 J/kg for the
most unstable parcel), a well agreed upon solution by the short-
term guidance. Stronger forcing associated with the initial
boundary is generally situated north of our area into northern
Wisconsin which is where the CAMs are trending the bulk of
precipitation. Low level capping may also limiting convective
potential across northeast Iowa into southern Wisconsin noted in
model soundings.

As the cold front moves southeast through the region overnight
behind the initial wave, a few elevated storms may be able to
develop along it despite weak convergence and the aforementioned
low level capping. Instability isn`t expected to be overly
impressive along the front given the overnight timing and
influence from the afternoon convection with skinny profiles of
500-1000 J/kg MLCAPE, waning with southeastward extent. Wind
shear overnight is also expected to be on the weaker side as the
strongest winds reside further northwest behind the cold front,
although 25-35kts of 0-6km bulk shear is depicted, in the
unlikely scenario parcels are able to become surface based.
However, elongation in the hodographs could support a stronger
updraft despite a weaker effective shear.

Areas in southeast Minnesota to north-central Wisconsin appear
to be the most favorable locations for a stronger storm, but the
overall strong to marginal severe threat is low. The SPC has
maintained a Marginal Risk (Level 1 out of 5) across portions of
our area.

Below Normal Temperatures and Shower Probabilities

Cold air advects into the Upper Midwest behind the cold front,
bringing Fall like conditions to the region for the weekend and
early next week. Current forecast highs sit in the mid 60s
across the region which is 10 to 15 degrees below normal for
this time of year. Lows will generally bottom out in the mid
40s. The current expectation is mostly clear skies during the
overnight hours, which would lead to lows falling lower. Tuesday
morning is currently the most favorable time to see lows in the
upper 30s across northern and central Wisconsin as the 21.13z
NBM indicates a 20-40% probability for temperatures < 40F, a
consistent solution over the past several runs.

Showers are possible Saturday and Sunday under steep low level
lapse rates associated with the cold air advection cyclonic flow
of the longwave trough situated over the Great Lakes, and ample
moisture through the 900-800hPa layer. The 21.13z NBM continues
with it`s low PoP bias this afternoon during this time period,
suggesting probabilities less than 20% whereas the 21.00z LREF
provides a better picture of the expectation of showers as
40-70% of the members depict this solution. Breezy conditions
will accompany the showers. Drier conditions are expected by
early next week as the upper trough and surface low begin to
migrate eastward, with surface high pressure building in behind
them.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1248 AM CDT Fri Aug 22 2025

VFR conditions expected for most locations through the TAF
period. A BKN deck of high level clouds has moved into the area
and is expected to linger through the night, inhibiting any
chances at fog to occur in the Mississippi River valley. There
is also an increase in low level winds right off the surface
that is playing against any fog developing along the valley.
Despite the high level clouds, some patchy fog will be possible
in portions of northeast Iowa and southwest Wisconsin. Shower
and thunderstorm chances increase (30 to 45%) during the
afternoon and evening as a boundary moves through ahead of a
cold front that will move through early Saturday morning. Light
south winds will gradually shift to southwest winds this
morning.



&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...Cecava