National Weather Service United States Department of Commerce


A strong, early spring storm moved across the region on the 9th and 10th of April 2011. On Saturday (April 9th), a warm front was the focus for severe thunderstorm development, and resulted in several tornadoes over northwest Iowa along with large hail and damaging winds.

On Sunday, April 10th, the warm front pushed north across northern Wisconsin. The severe weather focus shifted to a low pressure area and associated cold front that would eventually push through the region. The atmosphere was unstable ahead of the front with favorable winds for storm organization, which included Supercells capable of tornadoes.

Storms started to rapidly develop around 3 p.m. with many producing severe weather within 20 to 30 minutes of initiation. The storm movement was very fast - nearly 70 mph at times.

The severe thunderstorms produced very large hail, damaging winds, and a few tornadoes. Storm surveys confirmed two tornadoes in central Wisconsin (Adams / Waushara Counties) and wind damage in parts of Houston County, MN (near Caledonia) and around Osseo, WI. Hail up to 3 inches in diameter pelted the southern sections of La Crosse as well as neighboring areas in Minnesota. Car, roof, and siding damage was common. Golf ball sized hail fell at the NWS La Crosse office for a brief period.

There were 15 tornadoes in Wisconsin on Sunday, April 10th, which set a new record for the most ever for an April day in Wisconsin. The previous record was set on April 27, 1984, when 10 tornadoes occurred, with 3 fatalities and 42 injuries. That day in 1984 had two F4 intensity tornadoes which have winds of 207-260 mph. On Sunday, the strongest tornado surveyed was EF3 intensity (which has winds around 150 mph). For more information on the Wisconsin tornadoes, see the NWS Milwaukee summary, or the write up from .

Radar loop showing animation of rotation between 6:10-6:35 p.m.
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