795
FXUS63 KARX 281724
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1224 PM CDT Thu Aug 28 2025

.KEY MESSAGES...

- Areas to widespread valley fog likely late Tonight and Friday
  Morning.

- With there being better model consensus, added a slight chance
  (15-25%) of showers and storms for Friday.

- Added 15-25% chances of showers and storms in northeast Iowa
  and southeast Minnesota for the Labor Day weekend as low
  pressure systems undercut a 500 mb high centered over western
  Ontario and southern Manitoba. High temperatures will be
  mainly in the lower and mid-70s.

&&

.DISCUSSION...
Issued at 330 AM CDT Thu Aug 28 2025

This Afternoon and Evening

There will be 2 weak boundaries located in the region. The first
will be located along or just north of Interstate 90 and the
second one located closer to Interstate 80. With diurnal
heating, 0-1 km ML CAPES will climb up 500 J/kg. However, there
is weak surface convergence, capping near 700 mb, and limited
moisture, so the potential for thunderstorms looks unlikely.
Even the threat for showers looks to be isolated at best.

High temperatures will range from the upper 60s to upper 70s.
The coolest temperatures will be located along and north of
Highway 29 in Wisconsin.

Late Tonight and Early Friday morning

Bufkit soundings show light winds up to 850 mb and some shallow
moisture trapped underneath a nocturnal inversion. This should
result in the formation of valley fog. It should be widespread
in the tributaries of the Mississippi River valley and in the
Wisconsin and Kickapoo river valleys.

Friday

A shortwave trough will move southeast through the area. With
the 0-1 km ML CAPES climbing up to 1000 J/kg and decent surface
moisture convergence, there should be enough instability for
showers and storms. With weak shear in the 0-3 and 0-6 km shear,
not anticipating any organized severe weather. High temperatures
will range from the mid-60s to mid-70s.

Labor Day Weekend

There is better consensus that the 585 mb high will be centered
over western Ontario and southern Manitoba. This will allow for the
opportunity of undercutting low pressure systems to potentially
bring scattered showers and storms to southeast Minnesota and
northeast Iowa. However, the better chances still look to be
west of Interstate 35.

High temperatures will be mainly in the lower and mid-70s. The
coolest temperatures will be west of the Mississippi River (due
to the potential of rain and more clouds) and north of
Interstate 94. This still looks to be the coolest Labor Day
weekend since 2011.

Wednesday night and Thursday night

The models are in general agreement that a strong 500 mb closed
low will move into the Upper Mississippi River Valley or Great
Lakes. This low will likely bring anomalous cold temperatures
with it, but there is plenty of uncertainty on where this will
occur. The NBM probabilistic viewer continues to show large
spreads (up to 20 degrees) in the maximum and minimum
temperatures from the 10th to 90th percentiles. As a result,
the confidence remains low in the temperatures for this time
period. Due to this, just stayed with NBM 50th percentile.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1224 PM CDT Thu Aug 28 2025

Main taf concern through the taf period is fog development in river
valleys tonight into Friday morning. Surface ridge provides light
winds and mostly clear skies for much of the area tonight.
However...there are hints the scattered clouds over central
Wisconsin will expand over the rest of the forecast area
tonight. This could limit or inhibit the development of fog in
river valleys tonight. Depending on how widespread the cloud
cover is or where skies are clear...will determine fog
development in river valleys. If fog forms before clouds
form...visibility will be reduce to LIFR. If clouds expand over
the area...RST/LSE taf sites could see MVFR/IFR conditions. For
now...expect fog to form in river valleys and to be IFR
at LSE taf site after 09z Friday. Have brought in broken clouds
after 15z Friday at both RST/LSE taf site. Have kept ceilings
above 3000 feet. Though we could see a brief period of MVFR
conditions Friday morning.

&&

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

&&

$$

DISCUSSION...Boyne
AVIATION...DTJ