106
FXUS63 KARX 300148
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
848 PM CDT Mon Jun 29 2026

.KEY MESSAGES...

- Dangerous heat persists through at least Wednesday, but
  oppressive temperatures/humidity linger through late week. An
  Excessive Heat Warning remains in effect for most of the
  region while a Heat Advisory remains in effect for Taylor
  County in Wisconsin.

- Periodic storms are possible this week (20-40%), but
  timing/location remains uncertain. Storms that develop could
  become strong to severe.

&&

.UPDATE...
Issued at 819 PM CDT Mon Jun 29 2026

Increasing, Albeit Still Low Confidence Storm Threat Tonight:

Recent high resolution forecast model solutions have increased
agreement for storms initiating from far northeast Nebraska
through the MN/SD border to impact the local forecast area
tonight. While current radar imagery exhibits limited separation
between storms and storm motion, eventual interaction and
potentially collision between northern and southern storm
streams raises local concerns while limiting overall confidence
after midnight. While instability will be ample from steep mid
level lapse rates, overall shear values remain higher northwest
of the local forecast area outside of 0-1km.

The currently (30.0145Z) disjointed linear storm mode along the
MN/SD border, tied to the surface frontal boundary and a
phasing appendage of the synoptic low on upper level water
vapor imagery, is expected to take a more easterly progression
through the late evening hours as the storms exiting far
northeast NE on radar imagery remain tied to enhancement of the
nocturnal low level jet on Central Plains VWPs, resulting in a
more northeasterly progression into tonight.

Should the linear storm mode progress east through the local
forecast area before the northeasterly multicellular storms
reach the local area, a cooler and more stable airmass would
limit storm strength. Where the storms do eventually collide,
currently forecasted over southeast Minnesota at 30.09Z in most
recent HRRR (30.00Z), a temporary spike in storm strength
remains concerning. Main severe hazard would be damaging winds
as warm cloud depths thicken as storms near the forecast area
with the 40k Donovan height isohyet situated from northwest
Iowa through northwest Wisconsin.

&&

.DISCUSSION...
Issued at 139 PM CDT Mon Jun 29 2026

This Afternoon - Tuesday: Dangerous Heat and Storm Potential

Dangerous heat is expected areawide over the next 24-36 hours.
A very moist airmass remains in place this afternoon with
dewpoints in the mid to upper 70s across much of the area which
is expected to remain in place throughout the day Tuesday. Overall
expectations are for temperatures to climb into the low to mid
90s given 850hPa temperatures of 20-22C, resulting in heat
indices around 75F tonight and in the upper 90s to mid 100s
during the day Tuesday.

There is some concern for strong/severe storms tonight, mainly
northwest of a line from Charles City, IA to Wausau, WI
(10-30%) though expectations are for most of (if not all of)
these storms to miss our area due to strong capping in place
given 700hPa temperatures of 12+C. However, there are some CAM
solutions suggesting a line of convection moves west-east
through the region after midnight on the nose of an
strengthening nocturnal low level jet and 850hPa moisture
transport. Confidence is low in which scenario will win out, but
currently leaning towards most storm activity remaining out of
our area as this has the greatest consensus amongst model
guidance. Regardless, if storms do affect the area tonight, the
primary hazard will be damaging winds.

Additional concern for strong/severe storms comes Tuesday
afternoon, mainly north of I-94 (20-30%). The expected heat and
humidity Tuesday will continue to support the volatile
atmosphere in place with MUCAPE values exceeding 3000 J/kg in
most model solutions along with effective bulk shear of
30-35kts. Within this environment, a surface boundary associated
with the surface low over southern Canada lays out and stalls
from northeast to southwest from northern Wisconsin to northern
Iowa with the favorable atmosphere in place ahead of it. Above
the surface features, a ribbon of 700hPa positive vorticity and
divergence associated with the right entrance region of a nearby
jet core could support storm development, although the overall
QG forcing is fairly weak and nebulous.

The biggest question is if convective initiation can even occur
in this environment. 700hPa temperatures remaining around 12C
may make it challenging for convection to develop, especially
given the nebulous forcing. Many CAM solutions do suggest the
bulk of development remains across northern Wisconsin. There is
also the issue of how the storms overnight evolve and their
influence on where mesoscale boundaries set-up which would also
influence convective initiation. All of this said, if
convection is able to develop, expectations are for damaging
winds to be the primary threat. The aforementioned warm
temperatures aloft make large hail unfavorable as WBZ heights
are forecast to be above 10kft, but certainly can`t rule out
some smaller stones up to 1 inch given the ample instability.

Wednesday - Friday: Hot/Humid Conditions Continue and Storm Chances

Wednesday morning brings additional strong/severe storm
potential (50-70%) along the aforementioned stationary boundary
as it lays out west-east across the region. A subtle shortwave
lifts northward atop this feature with ample moisture remaining
in place. MUCAPE of 2500+ J/kg will exist along the boundary
with 30-35kts of effective bulk shear. Damaging winds and hail
up to 1 inch again seem possible with storms that develop during
this period.

Slightly cooler temperatures are depicted in ensemble suites
Wednesday through Friday as the upper ridge begins to shift ever
slowly eastward although temperatures still remain in the upper
80s to low 90s. The evolution of any possible convection may
also act to further temper afternoon highs. However, dewpoints
remain in the low to mid 70s and with little temperature relief
overnight, confidence is high in heat impacts lingering through
at least Wednesday.

Holiday Weekend - Early Next Week: Seasonable, Additional Showers
and Storms

As we head into the holiday weekend, the upper level pattern
becomes more zonal as compared to today/Tuesday allowing various
shortwaves to traverse the mean 500hPa flow. These shortwaves
will tend to knock down temperatures aloft as well as at the
surface with an overall cooling trend noted in the 29.00z LREF.
Surface highs fall into the low to mid 80s, near normal for this
time of year, although there is a fair degree of uncertainty in
exact temperature values as the 25th-75th percentile spread is
around 5-10 degrees with some outliers still suggesting the 90s
could be in play. Additional shower and storm chances also exist
over the holiday weekend with the 29.13z NBM currently
suggesting 30-60% probabilities for measurable rainfall, but
there is still plenty of variation to work out over the coming
days.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 642 PM CDT Mon Jun 29 2026

Mostly VFR conditions with sct to bkn low-level clouds will give way
to some storm potential tonight as a convective system treks
eastward into the local area. Currently, confidence is not overly
high (20-40%) that storms will reach either TAF site tonight,
however given the latest trends in the CAMs have opted to
include a prob30 for both KLSE and KRST with the potential for
IFR vsbys if storms do occur. Storms that do occur may be strong
to severe with hail and gusty winds. Otherwise, some LLWS is
possible with an increasing low-level jet overnight to around
50 kts with decreasing sfc winds. Winds will begin the TAF
period at around 15-20 kts with gusts up to 30 kts before
diminishing to around 10 kts overnight.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Extreme Heat Warning until 9 PM CDT Tuesday for WIZ029-032>034-
     041>044-053>055-061.
     Heat Advisory until 9 PM CDT Tuesday for WIZ017.
MN...Extreme Heat Warning until 9 PM CDT Tuesday for MNZ079-086>088-
     094>096.
IA...Extreme Heat Warning until 9 PM CDT Tuesday for IAZ008>011-018-
     019-029-030.

&&

$$

UPDATE...JAR
DISCUSSION...Falkinham
AVIATION...Naylor