textproduct: La Crosse

KEY MESSAGES

- Hazardous heat continues this afternoon with the heat index rising to near 100. Temperatures will moderate slightly over the coming days and triple digit heat index values, present this afternoon, will likely be in the rear view mirror outside of some river valley locations.

- Smoke from Canadian and northern Minnesota wildfires will affect at least part of the area over the next couple days. Locations north/east of I-94 will be most affected and could see visibility below 1 mile and very unhealthy (level 5 out of 6) to hazardous (level 6 out of 6) air quality.

- Largely diurnal potential (10-40%) for showers and thunderstorms Thursday through Saturday.

DISCUSSION

Issued at 155 PM CDT Wed Jul 15 2026

Heat continues, but moderates after this afternoon

Strong upper ridge is present over an axis extending from over Sioux Falls to the Tidewater region. This, combined with the slight increase in moisture over the past few days, has led to heat index values finally reaching the triple digits more than sporadically for the first time through our ongoing Heat Advisory. Moving ahead to tomorrow, heights aloft continue to fall with the drop in air temperatures leading to the heat index remaining below 100. Given this, the struggle to reach 100 in previous days, and nighttime temperatures that dropped into the 60s Monday and Tuesday nights, and potential for smoke to prevent some heating tomorrow - more on that below - will refrain from extending the Heat Advisory beyond this evening.

Smoke and hazardous air quality ahead

Areas of wildfires in northern Minnesota and western Ontario have continued over the past several days. Smoke from these fires has spread over Lake Superior given northwesterly flow through much of the column. Winds around 850mb have turned to out of the north/northeast, bringing some of this smoke into Clark/Taylor Counties with visibility down to around 1 mile at MDZ. 15.12z HRRR and 15.15z RAP smoke output suggest this area of smoke will at least spread to closer to I-94 with the RAP bringing it near to the Mississippi. Latest indications from MN/WI state air quality outlooks are that level 5 (very unhealthy) to 6 (hazardous) conditions will be present where smoke is thickest, mainly along and north/east of I-94. 15.15z RAP suggests near surface smoke will begin to improve Thursday afternoon into Friday as southerly flow near the surface ramps up due to a lee surface trough developing in the central High Plains.

Thunderstorm potential returns

Return of northwesterly flow aloft will also bring chances (10-40%) for thunderstorms Thursday through Saturday during the afternoon/evening hours. Each day should (70-90% for 1000 J/kg per 15.00z LREF) have sufficient instability for strong thunderstorms but shear needed for convective organization appears to be lacking, save for Saturday - but then the upper disturbance needed for thunderstorms to initiate may eject southeast several hours before peak heating. In summary, those with outdoor plans will need to remain alert for potential lightning starting Thursday, but severe storm concerns remain very low at this time.

AVIATION /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 622 PM CDT Wed Jul 15 2026

Both smoke and fog are the main concerns through Thursday. Dense Canadian wild fire smoke will gradually work south into the Interstate 90 corridor overnight. This smoke will then persist through the day along and north of Interstate 94.

With light winds up to 10K feet tonight, we will likely see valley fog develop. Dense fog is expected at KLSE from 06.10z through 06.14z.

ARX WATCHES/WARNINGS/ADVISORIES

WI...Heat Advisory until 8 PM CDT this evening for WIZ029-032>034- 041>044-053>055-061. MN...Heat Advisory until 8 PM CDT this evening for MNZ079-086>088- 094>096. IA...Heat Advisory until 8 PM CDT this evening for IAZ010-011-030.