Severe Thunderstorm Warning and Heat Advisory Issued Across Wisconsin as Two Storm Systems Develop

A severe thunderstorm warning has been issued across portions of Wisconsin as rapidly developing storm systems move eastward, bringing the threat of damaging winds up to 70 mph, large hail, and isolated tornadoes. Simultaneously, a heat advisory remains in effect for southeastern Wisconsin, with heat index values expected to surpass 100 degrees due to extreme humidity levels.

Rapidly Developing Storm Activity

A line of intense storms materialized across western counties in late morning, developing within just 30 minutes and moving toward Lake Michigan. The storms formed through a meteorological phenomenon known as gravity waves—cloud formations that push air upward and allow systems to tap into atmospheric energy created by heat and humidity. This rapid development caught forecasters off guard, as weather models had not predicted the activity.

Multiple severe thunderstorm warnings were issued for Jefferson and Waukesha Counties until 11:00 a.m., with a tornado warning extending across parts of southeast Wisconsin. Earlier tornado warnings that included northwest Oconto County have expired. The primary hazards include damaging winds, large hail, and heavy rainfall, with wind gusts potentially reaching 70 miles per hour.

Two Expected Storm Rounds and Extreme Heat

Forecasters are monitoring two separate rounds of severe weather activity. The first round brought immediate threats during late morning hours. A second round is expected to develop this afternoon between approximately 2:00 p.m. and 6:00 p.m., again along a cold front with potential for scattered severe thunderstorms and isolated tornadoes.

The heat situation compounds the weather threat. With delayed morning storm development, temperatures are climbing toward the low 90s across many locations. Combined with dew point values in the upper 70s, heat index readings are forecast to exceed 100 degrees for most of southeast Wisconsin. A Heat Advisory originally issued for western counties has been expanded to cover all of southeast Wisconsin and remains in effect until 9:00 p.m.

Forecast Outlook

Conditions are expected to improve significantly by the following day, with sunny skies and reduced humidity returning. High temperatures should reach near 80 degrees with more comfortable atmospheric conditions. Residents are advised to monitor local weather alerts and take shelter immediately if warnings are issued in their area.