366
FXUS63 KARX 262340
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
640 PM CDT Sun Jul 26 2026

.KEY MESSAGES...

- Dangerous heat today across much of the area with heat indices
  reaching 105-115 degrees south of I-94. Heat will likely
  continue into Monday with increased probabilities (50-70%) for
  heat indices over 100 degrees south of I-90.

- Increasing confidence for storms this evening and overnight
  with highest probabilities (40-60% chance) east of the
  Mississippi River. Some storms may be severe with damaging
  wind gusts and large hail being the primary threats.

&&

.DISCUSSION...
Issued at 200 PM CDT Sun Jul 26 2026

Today and Tonight: Dangerous Heat and Severe Storms

Low clouds have finally mixed out across much of the region with
some mid/high clouds rounding the crest of the ridge. Even with
these high clouds, many locations are already seeing early afternoon
heat indices in the high 90s to around 105 with continued climbing
expected through the duration of the afternoon. Dew points in the
low to mid 80s have been observed over portions of Central Iowa this
afternoon and southwest winds are slowly advecting this excessive
moisture into Northeast Iowa and beyond. The Extreme Heat Warning
will be in effect for most of the area until 9PM as dew points in
the 70s to low 80s areawide will keep heat indices over the century
mark well into the evening hours.

Given the very warm and unstable airmass in place over the region,
storms are expected to fire across portions of Northern
Minnesota/Wisconsin in the vicinity of Lake Superior later today as
a shortwave impulse rounds the ridge and starts to make its way
southeast into the Upper Midwest/Great Lakes region. This looks to
be the main focus for thunderstorm development but other weaker
impulses across the Dakotas/Central Minnesota could set some storms
off later this afternoon - though confidence in this scenario is
lower given convective debris from residual storms out west for
areas along the Minnesota/Iowa border. Forecast soundings across
Central Wisconsin show ample instability with 2000+ J/kg of MUCAPE
and 35-50 kts of effective shear just outside the periphery of the
ridge. Initial supercells across Northern MN/WI are expected to grow
upscale into more of an MCS type feature. Initial supercells would
pose an all-hazards risk, though primarily large hail and damaging
winds as 0-1 km shear and helicity is not looking overly
favorable for tornadoes. Steep lapse rates aloft around 8 deg
C/km would favor large hail growth but warm temperatures aloft
might temper this risk overall. Winds look to be the main threat
with forecast DCAPE values between 1000-1500 J/kg. As we move
through time and storms congeal into more of a cluster, wind
will become the prevailing threat, especially as this looks to
be happening into the evening/overnight hours where the
inversion will start to set up and storms will start to become
more elevated in nature. This cluster is expected to work its
way south/southeast through Wisconsin into the overnight hours
before moving off towards the Lake Michigan coastline.

Monday and Monday Night: Heat Risk Continues and Storm Potential

Skies will start to clear out behind the remnants of the morning
system and with dew points still in the 70s to low 80s across the
region, heat indices are once again expected to climb to between 100-
110 for many tomorrow, with the warmest conditions expected across
Northeast Iowa and Southwest Wisconsin. Locations further north and
west across Southeast Minnesota will start to see a slight reprieve
by the end of the day as a cold front starts to move through the
region, shifting winds to the northwest around noon. Though ambient
temperatures will still climb into the 90s for many, this will allow
some slightly drier air to start to mix in from the northwest, which
will start to fend off some of those upper 70s dew points, helping
to lower those across Southeast Minnesota. The rest of us will
unfortunately not feel the reprieve until Tuesday when temperatures
are in the 80s and dew points are back in the 60s.

Lingering activity from the overnight hours across West Central and
Southwest Wisconsin could pose a marginal severe risk as it will be
in an area of warm advection. The better lift will have passed with
the shortwave impulse earlier but enough lingering instability will
allow for a marginal hail and wind risk to persist into the morning
hours for our far eastern zones. Overall concern later in the day
tends to shift to the east as the upper trough and shortwave
impulses take aim more at the Great Lakes/Michigan than western
Wisconsin though some spotty showers and storms could pop up across
Central/Southwestern Wisconsin tomorrow afternoon on the periphery
of the ridge. Confidence in activity this far west tomorrow is much
lower (around 20%) with most likely staying dry.

Tuesday - Saturday: Warm Temperatures Continue with Storm Chances

The ridge shifts westward just enough and northwest flow remains in
place. Both of these will mean temperatures cool down slightly, into
the mid to upper 80s but it also means that the 70F dewpoints would
be less likely to occur. Heat indices will also stay in the 80s to
around 90F. With this flow pattern, ensemble guidance has low
precipitation chances through midweek with better chances as we head
towards the weekend. Another thing to note is that given the
northwest flow pattern, we will have to watch for any waves that
ride around the ridge as these would impact portions of the Upper
Midwest.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 640 PM CDT Sun Jul 26 2026

VFR conditions are expected through the TAF period with the
potential for storms east of the Mississippi River late this evening
and into the overnight. Overall confidence has been decreasing for
overnight storms reaching the Mississippi River, however have opted
to maintain a prob30 at KLSE as some CAMs still suggest this
possibility. If any storms do manage to reach the TAF site, strong
wind gusts may occur, however the highest probabilities for storms
overnight are currently north and east of I-94. Otherwise, a frontal
passage during the afternoon on Monday will switch winds from
southerly to northwesterly and will increase to around 10-15 kts.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Extreme Heat Warning until 9 PM CDT Monday for WIZ041-042-
     053>055-061.
     Extreme Heat Warning until 9 PM CDT this evening for
     WIZ032>034.
     Heat Advisory until 9 PM CDT Monday for WIZ032>034.
     Heat Advisory until 9 PM CDT this evening for WIZ017-029.
     Heat Advisory until 9 PM CDT Monday for WIZ043-044.
MN...Extreme Heat Warning until 9 PM CDT Monday for MNZ096.
     Extreme Heat Warning until 9 PM CDT this evening for MNZ079-
     086>088-094-095.
     Heat Advisory until 9 PM CDT Monday for MNZ079-086>088-094-095.
IA...Extreme Heat Warning until 9 PM CDT Monday for IAZ008>011-018-
     019-029-030.

&&

$$

DISCUSSION...Barendse/Naylor
AVIATION...Naylor