April 10 2011 will go down as the biggest daily April tornado outbreak (in terms of total tornadoes) in Wisconsin history. The other big April tornado outbreak was on April 27 1984, when 10 tornadoes occurred, of which 6 were considered at least strong. This included the violent Wales Tornado in Waukesha County, rated an F4, and another F4 tornado in Winnebago and Outagamie Counties.
The EF3 tornado on April 10, 2011 occurred near Merrill in Lincoln County. EF2 tornadoes were also documented in Adams County, Forest County, and Brown County (see table and graphic below for locations).
These are the first strong tornadoes in 17 years for the month of April in Wisconsin (the last being April 26 1994 in NW Wisconsin). They are also the first strong tornadoes in 27 years in the month of April for central or southern WI (April 27 1984).
Damage assessment continues, which means more tornadoes may be found and recorded in the next few days. Below is a rough plot of the tornado locations and EF-rating.
Below is a listing of the April 10th tornadoes in Wisconsin...subject to change as new information becomes available.