Why do Minnesota and Wisconsin experience so many damaging thunderstorms, considering how far north they are?

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Dear Tom,
Why do Minnesota and Wisconsin experience so many damaging thunderstorms, considering how far north they are?
— Margaret Robertson, Chicago
Dear Margaret,
Severe thunderstorms can occur anywhere, given the necessary meteorological conditions of warmth, moisture, instability, converging low-level winds and diverging winds aloft. The upper Midwest gets its fair share of severe weather, with the time of highest incidence from midsummer through early fall. The region is prone to derechos, a long-lasting high wind event in which down burst winds, at times in excess of 100 mph, plow out of a line of fast-moving thunderstorms, producing swaths of damage that extend for hundreds or even thousands of miles. Iowa meteorologist Gustavus Hinrichs coined the term “derecho” in the 1880s, a Spanish word meaning “straight ahead.”

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