Minnesota has seen 48 preliminary tornadoes so far this year, topping its average of 46 annually between 1991 and 2010. Tornadoes generally occur from May through September, and from 2 p.m. to 9 p.m.

If you've been hearing more about tornadoes this spring than recent years, there's a reason for that: So far this year, the U.S. has seen more twisters reported by early May than in any year since ...