Wisconsin, while not in “Tornado Alley,” experiences a significant number of severe weather events, including confirmed tornadoes. The state’s position in the Upper Midwest means it regularly encounters the atmospheric conditions necessary for rotating thunderstorms. Understanding the timing and intensity of these events is a focus for weather observers and the general public. While powerful tornadoes are rare, the threat of a damaging storm remains a yearly concern. The most recent confirmed tornado provides a snapshot of this ongoing severe weather risk.
Details of the Last Confirmed Tornado
The last confirmed tornado in Wisconsin occurred on September 22, 2025, near Mt. Sterling in Crawford County. It was officially classified as an EF-0 on the Enhanced Fujita (EF) Scale, signifying estimated wind speeds between 65 and 85 miles per hour.
This tornado was a relatively weak and brief event, common for funnels that touch down in the state. An EF-0 typically causes light damage, such as peeling surface material from roofs, snapping small branches, or pushing over shallow-rooted trees. The National Weather Service assessment confirmed this damage pattern near Mt. Sterling.
The tornado was the 39th documented twister in Wisconsin for the 2025 season, significantly exceeding the state’s annual average. Earlier that year, the state experienced more destructive events, including two EF-2 tornadoes that struck Dodge County on May 15th. These stronger events, with wind speeds up to 135 mph, caused significant damage to homes and businesses in the Juneau and Mayville areas.
The late September timing for the last confirmed tornado is unusual, as the state’s severe weather season typically begins to wane. Tornadoes outside the peak summer months are often associated with strong, late-season low-pressure systems. The minimal damage near Mt. Sterling serves as a reminder that the threat of a tornado does not disappear until colder weather is established.
Seasonal Patterns of Wisconsin Tornadoes
Wisconsin averages approximately 23 confirmed tornadoes annually. The most active period for tornado formation is during the late spring and early summer months.
The peak tornado season stretches from May through August, with the highest frequency historically occurring in June and July. This timing corresponds to when the state experiences the optimal combination of warm, moist air from the Gulf of Mexico and dynamic weather systems from the west. These ingredients provide the necessary instability and wind shear for severe thunderstorm development.
Geographically, the southwestern third of the state is statistically the most prone to tornado activity. This area, including counties near the Mississippi River and the Driftless Area, averages roughly one day per year with a confirmed tornado. This frequency gradually decreases across the state, with the northern regions experiencing a lower overall risk.
How Tornado Events are Verified
The official classification of a tornado falls under the authority of the National Weather Service (NWS). A preliminary report from a trained spotter or emergency management is the first step, but official confirmation requires detailed analysis.
Meteorologists first examine Doppler radar data, which detects the characteristic rotation within a thunderstorm known as a mesocyclone. The radar can also identify a “debris ball,” indicating a vortex strong enough to loft material into the air. However, radar confirmation alone is not sufficient to assign a final rating.
NWS storm survey teams are dispatched to the affected area to conduct a ground assessment of the damage. These teams use the specific patterns of destruction to determine the tornado’s path, width, and its final rating on the Enhanced Fujita (EF) Scale. The EF-Scale rates a tornado from 0 to 5 based on estimated wind speeds derived from the degree of damage to 28 different types of structures and vegetation.
The EF-Scale is an improvement over the original Fujita Scale, using refined damage indicators and corresponding wind speed estimates for a more accurate classification. This ground survey ensures that an event is confirmed as a tornado and correctly categorized according to the severity of the winds it produced.