textproduct: La Crosse

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 /12Z TAFS THROUGH 12Z MONDAY/

Issued at 535 AM CDT Sun Jul 12 2026

VFR conditions are expected throughout the TAF period with clear skies. Winds will remain around 5 kts from the southeast for much of the local area.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...None. IA...None.