textproduct: La Crosse

KEY MESSAGES

- Widespread thunderstorms likely this evening (75% to 95% chance), with moderate rainfall rates, and near-zero severe weather potential.

- Thunderstorms likely (50% to 80% chance) tomorrow late afternoon/evening in southwestern Wisconsin. - Probability increasing of major heat impacts (20% to 40% chance) starting on Sunday and lasting into next week.

DISCUSSION

Issued at 255 PM CDT Tue Jun 23 2026

This Afternoon and Tonight

At 2 pm this afternoon, there were thunderstorms over west-central to central Minnesota. These storms were not severe, and produced rainfall rates of around 0.25 to 0.5 inches per hour. These storms were associated with the leading edge of a somewhat vertically stacked area of low pressure that is slowly propagating eastward along the Canada/US Border over North Dakota.

Timing-wise, these storms are slated to reach the ARX CWA towards the end of peak heating from 6pm - 8pm. With instability waning, MUCAPE values will struggle to reach 500 J/KG, and 0-6km shear values struggle to reach 30 kts. In all, there are not the parameters present to support severe weather development, and the severe weather potential is near-zero. Several rounds of storms are likely to last into the overnight hours, with rainfall rates waning towards sunrise.

Rainfall rate-wise, there are actually some parameters that suggest moderate rainfall rates are possible with these storms. More specifically, there is around a 60% chance of rainfall rates reaching 1 inch per hour. Thus, have trended total expected rainfall upwards to closer to the 0.75 to 1 inch range. The large slug of moisture/saturation within the 0-6km layer moves east of the ARX CWA by 12z Wed, ending the most intense rainfall. Given the antecedent dry conditions and time of year, no flooding is expected at this time.

Wednesday

The core of the aforementioned low pressure pivots and meanders along Lake Superior Wednesday into Wednesday night, keeping thunderstorms in the forecast for Wednesday afternoon/evening. At this time, there is a 'marginal' risk for severe weather for the eastern tier our Wisconsin counties (Clark, Taylor, southward through Grant County)- that features a 5% chance of large hail, 5% chance of damaging winds, and a 2% chance of a tornado within 25 miles of a given point. Sporadic clearing may aid instability and support MUCAPE values nearing 1000 J/kg. A weak cold front passing through Wednesday evening with the accompanying low may be enough to get storms rooted a little closer to the surface and less purely elevated in nature... hence the 'marginal' severe risk. Will monitor overnight trends.

The overall heavy rainfall parameter space is not present. So am struggling to see mean precip values being much above the 0.1 inch to 0.2 inch range for Wednesday evening.

Thursday through Saturday

Zonal flow will be found across much of the northern US. Depending on the timing of shortwave troughs, there are small chances (10% to 15% chance) of showers and storms. High temperatures will be in the mid to upper 70s, to the low 80s on Saturday.

Sunday through Monday

Probability increasing of major heat impacts (20% to 40% chance) starting on Sunday and lasting into next week. As a longwave trough in the western US amplifies, an upper level ridge will build across the Upper Mississippi River Valley from Saturday through Monday. This pattern will be persistent through much of next week, making above-average temperatures likely (80%+ chance) into the July 4th weekend. By the middle of next week, there is a 60% to 80% chance of 'Moderate' heat risk impacts- impacts that will affect those who are sensitive to heat, especially those without cooling/hydration.

Depending on the position of this ridge, there may be periods of storms throughout the week (20% to 50% chance).

AVIATION /00Z TAFS THROUGH 00Z THURSDAY/

Issued at 630 PM CDT Tue Jun 23 2026

Showers and storms currently across south-central Minnesota into northwestern Wisconsin continue southeastward along a surface front through the evening and overnight hours (50-80%) bringing periods of MVFR/IFR ceilings and visibilities. Expectations are for these showers/storms to move out of our area around 10z Wednesday while MVFR/IFR stratus lingers for a few hours in their wake, most favorable for those north of I-94 per the 23.18z REFS (60-80% for ceilings <3kft). Skies begin to clear late Wednesday morning with additional showers and storms developing during the afternoon hours (40-70%), although expectations are these will be isolated to scattered in nature. The greatest potential for showers and storms exists across Wisconsin during this period. Outside of the showers/storms, south to southwest winds continue through the evening and overnight hours, slowly veering to the west and northwest behind the front.

ARX WATCHES/WARNINGS/ADVISORIES

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