108
FXUS63 KARX 201037
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
537 AM CDT Thu Aug 20 2026

.KEY MESSAGES...

- Showers and storm potential later this afternoon through the
  overnight with the highest chance for storms (40 to 70%) in
  western Wisconsin.

- Seasonal temperatures in the 70s to lower 80s are forecast
  each afternoon into early next week.

&&

.DISCUSSION...
Issued at 1200 AM CDT Thu Aug 20 2026

Today - Friday: Dry This Morning, Showers and Storms During the
Afternoon and through the Overnight

A cooler and drier air mass remains in place into the early
afternoon. Temperatures this morning will fall into the mid 40s
(along and north of I-94) to mid 50s. With light and variable winds
combining with clear skies, river valley fog is expected across many
river valleys this morning. This fog should lift by the mid-morning.
Heading into the afternoon shortwave trough and associated surface
low begins to move across northern Minnesota and far southwestern
Ontario. Ahead of this low, moisture advection increases helping to
kickoff a line of showers that may make it into our northwestern CWA
by the mid-afternoon, however with these showers fighting drier sub-
cloud layer air, it will be difficult for these showers to make it
any further. During the evening, a little instability builds into
(generally less than 1000 J/kg of MLCAPE) the CWA, still ahead of a
cold front that will eventually make its way through the forecast
area on Friday. CAMs have supported a second line of clusters of
storms forming behind the initial line of showers. With the limited
instability and weaker shear expected, there is a low chance for
organized severe weather to happen. These storms look to outrun the
instability gradient as the early morning progresses. One thing that
has been a little development with some of the more recent CAMs is
highlighting another area of storm development along the theta-e
gradient as it moves through the region. This particular area would
have greater instability so some stronger storms may be possible for
portions of northeast Iowa and far southwest Wisconsin during the
early afternoon. While the better severe potential remains off to
our west for this evening and to our southwest (better shear across
Central Plains) for Friday, some gusty winds and small hail may be
possible with some of the storms that impact our CWA.

This Weekend into Early Next Week: Seasonal and Mostly Dry Conditions

Forecast guidance remains consistent in building a ridge off to our
west and having it gradually weaken over our area during the
weekend. This would lead to mostly dry conditions as the wave paths
would be to our north through Sunday. A weak wave moves from the
northern Plains into the central Plains on Monday which could give a
small chance of showers and storms but the better potential looks to
be on Tuesday. Ensemble and deterministic guidance continues to
favor a low coming down into the Upper Midwest and an associated
cold front potentially providing a line of storms to pass through
the area. We will continue to monitor as there are quite a number of
details to work out before next Tuesday, such as how does the
previous day`s precipitation impact Tuesday`s chances. One thing
that is of higher confidence is the temperatures as our area would
remain under the influence of a trough that will keep temperatures
seasonable. Highs are looking like they will be in the low 70s to
low 80s from Saturday through Monday.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 537 AM CDT Thu Aug 20 2026

Valley fog has developed on the mainstem of the Mississippi River
and is on the doorstep of KLSE this morning. While daybreak will
shortly aid in mixing fog out in the coming hours, the prevailing
southeast drainage wind at KLSE may be enough to push fog into the
terminal prior to it lifting resulting in vsby reductions.
Consequently, have maintained a tempo for IFR reductions at
KLSE to address this potential through 13z. Otherwise, VFR
conditions are expected throughout much of the daytime hours
with south to southwesterly winds at around 8-12 kts. Shower and
storm chances increase later tonight as much of the CAMs bring
some convection near and north of I-90 after 00z with an
approaching disturbance. As a result, have added a prob30 at
KLSE to address the potential for category reductions during the
late evening and overnight hours.

&&

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

&&

$$

DISCUSSION...Cecava
AVIATION...Naylor