textproduct: La Crosse

KEY MESSAGES

- Dangerous heat persists through Wednesday with heat indices in the mid 90s to low 100s. Oppressive temperatures/humidity lingers through late week.

- Periodic storms are in expected throughout the week, but timing/location remains uncertain. Storms that develop could become strong to severe.

- Seasonable temperatures for the holiday weekend, though shower/storm chances exist (40-60%).

DISCUSSION

Issued at 211 PM CDT Tue Jun 30 2026

This Afternoon - Wednesday Morning: Dangerous Heat and Storm Potential

Dangerous heat continues areawide this afternoon under a stout upper level ridge that remains situated overhead. Observed dewpoints in the mid to upper 70s combined with temperatures in the low to mid 90s has resulted in heat indices in the upper 90s to mid 100s already this afternoon. Little in the way of airmass change is expected during the overnight hours which will result in heat indices only falling into the low to mid 70s, leading to little relief from the heat.

Apart from the heat, a 700-500hPa shortwave trough and associated vorticity maximum moves northward along the western edge of the aforementioned upper ridge overnight atop a surface boundary that lays out across the Upper Mississippi River Valley. Showers and storms are expected to develop in response to this wave within an unstable environment as the 30.17z RAP suggests MUCAPE of 2000-3000 J/kg should be in place. 0-6km shear also increases during this period, mainly west of the Mississippi River as the 500hPa wind field strengthens. 0-6km bulk shear values are forecast to be 40- 45kts, but given an expected elevated nature to these storms, effective bulk shear may only reach 20-25kts. Regardless, strong to severe storms will be possible in this environment, most favorable west of the Mississippi River, with damaging winds the primary threat. Lower end potential for large hail does exist though it's tied mainly to any supercell activity given the warm antecedent conditions and WBZ heights around 12kft.

Wednesday Afternoon - Friday: Storm Potential and Lingering Hot/Humid Conditions

Hot and humid conditions continue through the next few days, although slightly tempered as compared to the last couple of days. Highs are expected to top out in the upper 80s to low 90s Wednesday with another day of heat indices in the mid 90s to low 100s given dewpoints remaining in the low to mid 70s. That said, high temperatures may be further moderated depending on how the morning convection Wednesday evolves, which would effect how high heat indices make it. Regardless, oppressive heat and humidity will continue over the next few days.

Additional storms are possible through the afternoon hours Wednesday (10-20%), but will largely be dependent on where any differential heating boundaries and/or outflow boundaries from the morning convection set-up as a lack of synoptic scale forcing will exist behind the morning's shortwave.

As we head into the late afternoon and evening hours Wednesday, another round of strong to severe storms appears favorable across the region as another shortwave impulse moves through the region. MUCAPE values in excess of 2500 J/kg are forecast across the region with 0-6km shear values of 40-50kts, strongest along and north of I- 0. Timing/location variations amongst the CAMs leads to somewhat low confidence in when/where storms will develop but the favorable thermodynamic and kinematic factors has led to a level 3/5 enhanced risk to be issued over portions of our area. Damaging winds are again expected to be the primary hazard, but large hail and a couple tornadoes cannot be ruled out.

Additional periods of showers/storms are possible Thursday (30-60%) and Friday (40-70%) as the upper level ridge begins to shift eastward and the persistent ridging pattern breaks down.

Holiday Weekend - Early Next Weekend: Seasonable Temperatures Return With Additional Shower/Storm Potential

As the upper level pattern becomes more zonal as we head into the holiday weekend, several shortwave impulses are depicted to traverse the mean flow by the deterministic global models. These waves should result a reprieve from this week's heat as they usher in cooler air, slightly cooling temperatures towards the mid 80s, more seasonable for this time of year. Outside of the more seasonable temperatures, there is the potential for showers and storms throughout the weekend (40-60%).

AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/

Issued at 1235 PM CDT Tue Jun 30 2026

Minimal impacts to aviation are expected through the afternoon hours for much of the region. A surface boundary generally along a line from KMDZ-KAUM currently is expected to spark some isolated showers and storms through the afternoon (10-30%), primarily north of I-90 after 20z-21z. Storms that do develop could be strong to severe with strong wind gusts the main hazard. Otherwise, winds this afternoon will be generally from the south to southwest around 10-15KT with gusts of 20-25KT, strongest west of the Mississippi River. Looking towards early Wednesday morning, greater shower/storm potential exists across the region (50-70%) which may bring MVFR ceilings/visibilities to the region along with additional strong/severe potential.

ARX WATCHES/WARNINGS/ADVISORIES

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