When does tornado season start?

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When does tornado season start?
June, 2004 tornado near Madison, WI by i am your hero

Wisconsin has had tornadoes in every month of the year except February. We can have tornadoes almost anytime, although the chances of having one in winter are pretty small.

We typically define the tornado season for a particular area as the time of year when tornado occurrence there is at its peak. Tornado season peaks in March and April in the Southeast but not until late June or early July in the Upper Midwest. For the entire U.S., May is the month with the greatest number of tornadoes.

For a tornado to occur requires the right ingredients coming together in a particular place. Severe weather requires warm, moist air near the ground and a change in wind speed and direction, or wind shear, with height above the surface. Since springtime is when the lower atmosphere is warming up, that’s when we start hearing about tornadoes. This continues through summer. Because vertical wind shear is closely related to the presence of a jet stream, tornado season typically starts in the Southeast of the U.S. in early spring and moves northward as the jet stream moves north.

On average, Wisconsin averages 19 tornadoes a year. Since 1982, Dane County has recorded 33 tornadoes which caused 66 injuries and killed two people. While any tornado should be considered life threatening, most tornadoes that occur in Wisconsin are considered weak, with wind speeds less than 110 mph.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.