Schools shuttered early and cities warned of probable power outages, as potentially dangerous thunderstorms threatened the Upper Midwest late Monday afternoon.

In northeast Iowa, southeast Minnesota and western Wisconsin, residents were bracing for storms that could bring high winds, tornadoes and hail the size of Ping-Pong balls. The Upper Midwest is accustomed to severe weather, but the high level of risk for very large hail and strong tornadoes caused alarm for state and local officials, who activated emergency operations centers and closed nonemergency city buildings.

“We always have severe weather, I guess, in Iowa,” said Superintendent Joe Carter of the Algona Community School District, about two hours north of Des Moines. “I think the difference with this one is the threat of really, really strong stuff, such as tornadoes, and with a Category 4 ranking of severity.”

A large area that includes Minneapolis and St. Paul is under a relatively high risk (Level 4 out of 5) for severe weather, according to the National Weather Service’s Storm Prediction Center.

At least five school districts across north central Iowa announced early closings on Monday afternoon. The Algona Community School District let out classes at 2 p.m. and canceled afterschool track and golf meets so that buses could get students home throughout the 500-square-mile district before storms descended by early evening.

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