textproduct: La Crosse

KEY MESSAGES

- Enhanced-risk of severe storms for much of the Upper Mississippi River from 3 pm and 9 pm. All severe weather threats will be possible.

- Dry weather from Tuesday through Saturday. Coldest day will be on Wednesday when high temperatures will be in the lower and mid-70s.

DISCUSSION

Issued at 1239 PM CDT Mon Jul 20 2026

This Afternoon and Evening

We are already seeing rapid recovery taking place in the wake of the mesoscale convective complex across north-central Iowa and south-central Minnesota. Temperatures are currently ranging from the mid-80s to lower 90s. Dew points are in the lower and mid-70s. This is resulting in surface-based CAPES of 3-4K. As the afternoon progresses, this air mass will spread into the Upper Mississippi River Valley ahead of a cold front extending from the Minnesota Arrowhead to the southwest tip of Minnesota. There is already scattered showers and storms along this front. These storms should impact the Upper Mississippi River Valley between 3 pm and 9 pm.

Further south, moderate to strong capping (10-12C 700 mb temperatures) has developed across western Iowa and far southern Minnesota. This should keep this sector relatively clean; thus, this instability reservoir should continue to be able feed storms this afternoon and early evening.

As a vigorous shortwave moves into the region this afternoon, the winds aloft will strengthen. This will result 0-6 km shear of 60-65 knots. As a result, initial storms will be likely supercells. The hodographs are exceptionally long from eastern portions or northeast Iowa northeast through central Wisconsin. If these storms can become orthogonal with the cold front, there could be a few tornadoes. SigTOR parameter is 8 in southwest Wisconsin.

In addition with large NCAPE and strong mid-level lapse, there could be some large hail with the earlier supercells. Over time as cold pools coalesce, damaging winds will become the primary threat. In addition, any surges along the line will have to be watched for the potential for a few QLCS tornadoes.

Tuesday through Saturday

High pressure will build across the area on Tuesday and then provide dry weather through Saturday. High temperatures will be primarily in the 70s and 80s. The coolest day will be on Wednesday when highs will be in the lower and mid-70s.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 615 PM CDT Mon Jul 20 2026

Despite storms having largely evaded the region through the afternoon, a cold front will continue moving eastward through the Upper Mississippi River Valley this evening. VFR to MVFR cumulus around 2.5-3.5kft along the front may give way to some showers and storms (20-30%), but will largely be confined north of I-90.

Behind the cold front, winds become northwesterly and skies clear for the overnight before an area of MVFR to possibly IFR (10-20%) stratus moves into the region Tuesday morning, most favorable along/north of I-90. This stratus deck breaks up and lifts slightly during the afternoon, resulting in SCT-BKN skies with cloud bases around 3-5kft. Breezy conditions are expected Tuesday, especially in the afternoon, as stronger low level winds are able to mix to the surface resulting in northwesterly gusts of 15-25KT, strongest west of the Mississippi River.

ARX WATCHES/WARNINGS/ADVISORIES

WI...None. MN...Heat Advisory until 7 PM CDT this evening for MNZ079-086-087- 094-095. IA...Heat Advisory until 7 PM CDT this evening for IAZ008-009-018- 019.