Tornadoes strike somewhere in Wisconsin every summer. The state averages 21 tornadoes annually, with a record 62 in 2005; there were 18 confirmed tornadoes in 2007.

The earliest mention of one is by Jonathan Carver, who visited the state in 1766 and noted the effects of a tornado in the vicinity of the present city of Chippewa Falls. The state's deadliest tornado destroyed the St. Croix Co. town of New Richmond in 1899. The single day on which the most tornadoes hit Wisconsin was Aug. 18, 2005.

For a through examination of tornadoes in Wisconsin history, see "Tornadoes in Wisconsin," Wisconsin Magazine of History 73:4 (1989-1990): 242-273, which includes a lengthy table listing the worst tornadoes, 1865-1984. Some of the worst tornadoes to hit the state since then are:

1984, April 26-27: an outbreak of tornadoes covered all but extreme northeast Wisconsin. 11 tornadoes were spawned by 2 squall lines that crossed the state. The first entered western Wisconsin the night of April 26th, and produced one tornado in Polk county and another in Wood county. The second squall line moved into western Wisconsin late in the morning of April 27th. This line produced 9 additional tornadoes, responsible for all the deaths and most of the injuries. The 2 strongest tornadoes, both rated F4, hit near Wales in Waukesha county, killing 1 and injuring 14, and in the St. Germain area on the border between Vilas and Oneida counties, killing 1 and injuring 8. Overall, the storms killed 3 and injured over 40 people. An estimated $28 million dollars in damage was done by the two squall lines.

1984, June 6-07: the Barneveld tornado in western Dane Co., rated F5, left 9 dead, 200 injured, and $40 million in damages.

1993, June: the month with the most recorded tornadoes in the state - 28 tornadoes

1996, July 18: the costliest tornado this century struck Oakfield. 12 people were injured and $40.4 million in damage was caused; F5 rating. This was part of a tornado outbreak that produced 12 tornadoes across the state, 10 in southern Wisconsin.

1998, Aug. 28: a Door County tornado produced a waterspout over the Bay of Green Bay which moved onshore southwest of Egg Harbor. It injured two people and carved a damage path more than a quarter mile wide; $7 million dollars in damage; F3 rating.

2005, Aug. 18: 27 tornadoes were documented that day in Wisconsin, making it the most confirmed tornadoes that have ever occurred in the state in a single day (breaking the previous record of 24 tornadoes set on May 8, 1988). By far the most significant tornado of the day developed at 6:15 PM near Fitchburg, about 5 miles south of Madison. This F3 tornado travelled about 20.0 miles into Jefferson County from Dane County, passing through Stoughton with maximum intensity and a width of one-half mile. In that community it destroyed or damaged 240 houses, left property damage of $44 million, killed one person and injured 23 more. Debris from the Stoughton area was found as far as two counties to the east. The storm frequently changed size and form, finally lifting near Busseyvillle after traveling 20 miles in 53 minutes of continuous track. Numerous other tornadoes occurred the same day, during and after this one; Fort Atkinson was struck three times by three different tornadoes on Aug. 18th.

National Weather Service; Milwaukee Sentinel March 20, 1978; Wikipedia; WHS Library reference file; Wisconsin State Journal July 20, 2008.

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