852
FXUS63 KARX 251104
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
604 AM CDT Sat Jul 25 2026

.KEY MESSAGES...

- Dangerous heat this weekend and Monday with daytime heat
  indices over 100 degrees expected across much of the local
  area, particularly on Sunday.

- Storm chances this weekend with the potential for some storms
  to become strong to severe. Damaging wind gusts and large
  hail would be the primary threats with any severe storms.

&&

.DISCUSSION...
Issued at 409 AM CDT Sat Jul 25 2026

Heat Building Today & Storm Potential:

A warmer and moisture laden airmass has begun to push into the
region overnight, a result of a slight eastward progression to
the fairly pronounced upper-level ridge into the region.
Consequently, expecting temperatures to respond accordingly with
mean apparent temperatures in the NBM reaching around 100
degrees for portions of southeast MN where a Heat Advisory
remains in effect. In addition to the heat, there are some low-
end potential for isolated storms generally near and north of
I-90 in Wisconsin where the thermal ridge is less prevalent and
daytime heating may allow for the capping inversion, that
resulted from the aforementioned warm advection, to break. If
convection can manifest late this afternoon and into the
evening, very favorable shear profiles noted by the elongated
mid-level hodographs would suggest any isolated storms could
trend supercellular, especially with around 2000-2500 J/kg of
MUCAPE to work with. In this environment, large hail and
damaging wind gusts would be possible with the aforementioned
shear and instability accompanied with relatively steep low-
level lapse rates and impressive DCAPE values to around 1500
J/kg due to a profound dry layer between 500-700mb (which may
work to inhibit convection as well).

Heat & Storm Potential Increasing Sunday:

Continued south to southwesterly surface flow will continue to
push a warmer airmass into the region through the weekend. As a
result, there are high probabilities (60-80%) in the grand
ensemble (GEFS/EC/Canadian ensemble) for heat indices to exceed
100 degrees with even some spots seeing heat indices nearing 105
degrees for Sunday. Given the confidence and in collaboration
with neighboring forecast offices, have converted Extreme Heat
Watch to an Extreme Heat Warning. The one caveat to this will
be exactly how convection evolves on Sunday as this ridge
nears...

Overall, convective evolution on Sunday appears fairly low
confidence with pronounced capping in place across many of the
model soundings and uncertainty on when various shortwave
perturbations would traverse the area. The main concern comes
later into the afternoon and evening as more favorable 500mb
flow moves into northern WI with stronger forcing for ascent,
however there remains uncertainty on how far east the ridge has
progressed. There remains a very possible scenario that the
ridge has pushed too far east through the local area that much
of the evening convection would keep north and east of the area,
however there are just as many solutions that would keep
convection in play across the local area. In this scenario, an
MCS trekking through the local area with a damaging wind gust
risk would be of highest concern. Overall, it`s inherently an inversely
proportional relationship: if the ridge pushes further east,
the confidence for dangerous heat indices (105F or greater)
increases further and storm chances decrease; if the ridge
struggles to push east, confidence for storms increases and
dangerous heat decreases.

Heat Confidence Decreases Into Monday:

By the time Monday rolls around, the upper-level ridge hardly shifts
much keeping our region in southwesterly surface flow to start the
day on Monday. Consequently, expecting highs to yet again reach into
the 90s for much of the local area with heat indices approaching 100
to 105 degrees south of I-90. As we head later into the day on
Monday, guidance generally agrees on pushing a weak front
through the area during the afternoon and evening. While
confidence is fairly low (under 15% chance) for anything to
develop along this front on Monday afternoon and evening at this
point due to the lack of convergence along it and a pronounce
dry layer in model soundings aloft, there remains respectable
instability and shear in place in the event thermal profiles do
become uncapped and forcing trends more favorably for
convection. Have continued the previous Extreme Heat Watch
Sunday night through Monday in collaboration with neighboring
forecast offices given current apparent temperature forecasts
only flirting near Warning criteria on Monday.

All said, confidence is fairly high for impactful heat through
Monday with some questions how any convection many affect
temperatures over this period. Convective trends are a bit lower
confidence due to the ridge and its resultant capping not clearly
defined across the area in model guidance. Shear profiles seem
consistently sufficient for the development for severe storms during
this period with elongated hodographs from a strong and persistent
250-500mb jet streak. But again, whether these can be utilized are
heavily dependent on how much the ridge builds into the region.

Tuesday - Friday: Staying Warm with Some Storm Chances

As we head into the rest of the upcoming work week, northwesterly
flow will allow temperatures to cool down just a hair but more
importantly will lower our dewpoints to keep heat indices out of the
100 degree territory. With northwesterly flow returning during this
period, will have to watch for any potential ridge-running
shortwaves as the aforementioned upper-level ridge retrogrades
slightly to the west. However, ensemble and deterministic guidance
do not highlight any specific features at this point, but the
pattern overall is favorable for these features to manifest.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 603 AM CDT Sat Jul 25 2026

Ongoing IFR to MVFR ceilings continue through the early morning.
Eventual daytime mixing with increasing diurnal heating will
ameliorate impacts through the morning hours.

Low chance of thunder through the daytime hours increases
through Sunday. Exact location, timing, and strength remain low
confidence (<20%) as overall forcing remains meager.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Extreme Heat Warning from noon to 9 PM CDT Sunday for
     WIZ032>034-041-042-053>055-061.
     Extreme Heat Watch from Sunday evening through Monday morning
     for WIZ053>055-061.
     Heat Advisory from noon to 9 PM CDT Sunday for WIZ029.
MN...Heat Advisory from noon today to 8 PM CDT this evening for
     MNZ079-086-087-094.
     Extreme Heat Warning from noon to 9 PM CDT Sunday for MNZ079-
     086>088-094>096.
IA...Heat Advisory from noon today to 8 PM CDT this evening for
     IAZ008-018.
     Extreme Heat Warning from noon to 9 PM CDT Sunday for
     IAZ008>011-018-019-029-030.
     Extreme Heat Watch from Sunday evening through Monday morning
     for IAZ008>011-018-019-029-030.

&&

$$

DISCUSSION...Naylor
AVIATION...JAR