190
FXUS63 KARX 120525
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1225 AM CDT Sun Jul 12 2026

.KEY MESSAGES...

- Building heat today through Tuesday with an increasing
  likelihood that a portion of our area may need heat headlines.

- Staying dry until later this week, with only small rain
  chances (20-30%) returning Thursday into Saturday.

&&

.DISCUSSION...
Issued at 1225 AM CDT Sun Jul 12 2026

This Morning: Small Chance for a Sneaky Shower/Storm North of I-94

A weak shortwave dropping south will interact with some instability
and PWATs near 1.5" over northern Wisconsin this morning. This may
allow for remnants of overnight convection from western Ontario to
hold together into northern Wisconsin. However, convective allowing
models differ quite a bit with how quickly they kill the incoming
showers/storms, and at most they suggest the activity would just
graze Taylor County.

Building Heat Today Through Tuesday

A stout upper ridge (+3 standardized anomaly) will amplify over the
Northern Plains today with heights building to ~600 dam over the
Dakotas by evening. Strong warm air advection will surge northward
into southern Manitoba and southwest Ontario through early Monday
before the 500mb high gradually drifts southeast and flattens out
either overhead or just to our west by Tuesday. This will cause the
toasty 850mb airmass to our north to sag southward into our area
Monday into Tuesday, moderating a bit as it does so. Latest
deterministic and ensemble guidance has trended a smidge warmer, now
bringing 850mb temps of 24 to 26C into our area.

Oppressive humidity was a major contributor to our most recent heat
headline event at the end of June, when dewpoints climbed in the
upper 70s to near 80. That will not be the case with this mini heat
wave, with dewpoints likely to max out in the low to maybe middle
70s. Combining the GEFS/ENS/GEPS ensemble datasets, dewpoints in the
upper 70s would be in the 90th percentile and higher, so those
readings are less likely this go around.

Consequently, the GEFS/ENS/GEPS has lesser confidence (10-30%) on
increasing apparent temperatures to 100F or higher for Monday and
Tuesday afternoon at this point. That being said, the aforementioned
850mb temperature increase may support higher confidence for
headline criteria heat indices than what ensemble probabilities may
suggest. In collaboration with neighboring offices, not planning on
issuing a Heat Advisory for portions of the area for Monday and
Tuesday at this current moment. However, if confidence
increases for heat indices near 100F or greater with new model
guidance, a Heat Advisory will likely be needed for portions of
the area in subsequent forecast updates.

Mid to Late Week: Still Rather Warm, Small Rain Chances Returning

By midweek the upper ridge flattens and retrogrades to over the
Central Plains. That puts the Upper Midwest in a northwest flow
pattern aloft Wednesday into Thursday, opening the door to periodic
weak ridge runner shortwave activity. A ribbon of modest
precipitable water looks to sag southward into the area with the
ridge flattening into Thursday. Despite the reintroduced moisture,
there is low confidence in timing and likelihood of rain chances
toward the end of the week given the weak forcing and uncertainty in
how much instability will be in play. Ensemble members would suggest
a low probability for rain perhaps returning as early as Wednesday
evening, but chances look to be a bit more focused (20-30%) between
Thursday afternoon into Saturday, particularly east of the
Mississippi River.

While the worst of our heat will subside by midweek, it does look to
remain rather warm into next weekend with the upper ridge still
holding over the central CONUS. The NBM carries high temperatures in
the mid 80s to lower 90s from Wednesday through Saturday across the
area.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1225 AM CDT Sun Jul 12 2026

VFR conditions with south to southeast winds at 5-10 kts are
expected for much of the TAF period. The only caveat to this is the
potential for valley fog on the Mississippi River at KLSE early this
morning with clear skies and light winds in place. Currently, the
most recent runs of the RAP/HRRR/RRFS show increasing winds just off
the deck between 08z to 10z this morning which lowers confidence (5-
10% chance) for 1/4SM fog when also considering dewpoint depression
trends at KLSE over the past few hours. That being said, cannot rule
out a period of IFR to LIFR fog or low-stratus for a period at KLSE
given the other favorable conditions.

&&

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

&&

$$

DISCUSSION...Kurz/Naylor
AVIATION...Naylor