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Storm Set-up

Two rounds of severe weather struck the region on August 13, 2010: one during the early morning hours and the other in the afternoon and early evening.  Damaging wind gusts and  heavy rain inducing flash flooding were the main severe weather impacts, with a tornado also touching down in southeast Minnesota. There was some hail, but generally small and isolated in nature.

There was ample moist and unstable air for the storms to tap into as a tropical-like airmass had been entrenched across the Upper Mississippi River Valley for about 2 weeks. As a result, any thunderstorm would be capable of producing very heavy rain with hourly rainfall rates of 1 to 2 inches. Prior to the severe weather of this day, the high humidity coupled with temperatures in the upper 80s to lower 90s produced dangerous heat. Heat advisories had been in effect for parts of the region for several days leading up to August 13.  

Early morning

Severe thunderstorms were moving across much of Minnesota Thursday evening, the 12th. The storms started to push into southeast Minnesota and western Wisconsin during the overnight hours. The storms developed bowing segments, bringing winds in excess of 60 mph. One of these bows traveled east across southeast Minnesota, near Stewartville, but weakened as it reached the Mississippi River. The other bowing segment tracked from Wabasha County into western Wisconsin, moving from near Oak Center, MN to Modena, WI and then east southeast in the vicinity of Interstate 94. 

There were many reports of trees and power lines down due to the strong wind gusts.  

 Afternoon and early evening

The clouds and rain lingered in the late morning, but sunshine to the west destabilized the atmosphere. Again, a very moist air mass helped fuel more thunderstorm development. The main focus for this batch of severe weather was a west to east surface boundary across southeast Minnesota into southern Wisconsin.

Radar animation of tornado near Hayfield, MN on August 13, 2010
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