April 10, 2011: Straight-line wind in Waukesha County

An outbreak of severe thunderstorms, caused by low pressure moving from southwest Minnesota across northwest Wisconsin, produced 10 tornadoes in Wisconsin, which tied a record for the largest number of tornadoes in one day in the month of April in the state. Southern Wisconsin was in the warm sector of the system for most of the day, with a capping inversion preventing thunderstorm development until early in the evening. The exit region of an upper jet helped break the cap, with severe super-cell thunderstorms rapidly developing in an unstable environment, with surface-based CAPE of 2000 J/kg and strong vertical shear. There was one tornado reported in the Milwaukee/Sullivan County Warning Area, an EF0 tornado that tracked across northeast Green Lake County just southeast of Berlin. Severe thunderstorms produced damaging winds in Waukesha and Milwaukee counties.