670
FXUS63 KARX 300902
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
402 AM CDT Sat Aug 30 2025

.KEY MESSAGES...

- Fog and low stratus continue through the mid-morning hours.
  Visibilities are lowest over north-central Wisconsin and
  portions of northeast Iowa. Fog could be dense at times.

- Mostly dry conditions through the Labor Day weekend with low
  probabilities (< 20%) for showers and storms each afternoon in
  northeast Iowa. More widespread showers and storms possible by
  midweek (40-60%).

- Near-normal temperatures through Tuesday, then below normal
  temperatures through the end of the week.

&&

.DISCUSSION...
Issued at 400 AM CDT Sat Aug 30 2025

Today and Sunday

Patchy fog has developed across portions of north-central
Wisconsin and northeast Iowa this morning where skies remained
clearer overnight but have since become cloudy. Fog across these
areas could become dense at times, but visibilities are expected
to largely stay at 1 mile or greater. Elsewhere, low stratus
has largely hindered fog development. Fog and low stratus will
begin to mix out this morning with partly to mostly cloudy skies
taking hold through the afternoon.

The weak surface boundary that`s been stalled over portions of
southeast Minnesota and northeast Iowa the past few days has
shifted southwest towards central Iowa. There is some
uncertainty in just how far southwest the boundary has shifted,
so have kept low probabilities for a shower or two to scrape a
few of our Iowa counties this afternoon (< 20%), but confidence
is high that the vast majority of the region will remain dry. If
a shower is able to develop this afternoon, a rumble of thunder
can`t be ruled out as MLCAPE of 250-500 J/kg builds into our
area, although better instability lies to the southwest.

Given the influence of high pressure continuing into Sunday,
conditions would suggest fog is possible again tonight into
Sunday morning. Uncertain in how widespread fog would become,
but the typical low lying areas and river valleys are the
favored locations for fog development tonight.

Shower/Storm Probabilities Midweek

Tuesday into Wednesday, a closed 500hPa low dives southward out
of Canada into the Great Lakes region, forcing a cold front
through the Upper Mississippi River Valley. Showers and storms
become more probable along this front (40-60%), although current
timing suggests the front moves through the region late Tuesday
into Wednesday which would decrease instability and hinder
convective development. PWATs ahead of the front are expected to
be between 0.8-1 inch, so QPF associated with these showers and
storms should be fairly light. The 29.12z LREF highlights the
probability of 24hr QPF greater than 1/2 inch is 20-30%, with
higher probabilities over northern Wisconsin.

Near Normal Then Cooler

Through the Labor Day weekend, expect high and low temperatures
to be near normal under high pressure and little in the way of
airmass change. Towards midweek behind the cold front, ensemble
guidance strongly favors below normal temperatures being ushered
into the Upper Mississippi River Valley. Dependence on how cold
temperatures get remains on depth of the 500hPa low as
variations in heights remains evident amongst the 30.00z
GEFS/EPS/GEPS. However, 80-90% of the 29.12z ECMWF EFI members
indicate anomalous cold in the wake of the front, with the
30.01z NBM depicting temperatures generally 10 to 15 degrees
below normal by the end of the week.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1237 AM CDT Sat Aug 30 2025

The main concern overnight is how widespread the dense fog will
become. With light winds up to 800 mb, mostly clear skies, and
a nocturnal inversion trapping low level moisture, conditions
will be favorable for this dense fog to expand. We will continue
to monitor and adjust accordingly. This fog and dense fog should
dissipate around 30.14z.

&&

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

&&

$$

DISCUSSION...Falkinham
AVIATION...Boyne