Heavy snow blanketed parts of Iowa and Minnesota on Friday, closing and delaying some schools.

Northern Iowa got up to 9 inches of snow, while Mankato, in southern Minnesota, reported 7 inches. Severe thunderstorms in eastern Iowa produced dime- and nickel-sized hail.

In the northeastern Iowa town of Emmetsburg, the snowfall came along with thunder and lightning, in a phenomenon called thundersnow, said Craig Cogil, a meteorologist with the National Weather Service in Johnston.

"We checked in up there and they had 3 1/2 inches, and an hour later they had 7," he said.

The heavy snow was expected to begin breaking up by afternoon, Cogil said, but some area schools closed for the day or opened late because of the weather.

In Emmetsburg, residents were still busy, said Connie Boone, manager of a Casey's General Store.

"People are just as active because now they have to get out and shovel," she said.

Meanwhile, storms brought heavy rain, strong winds and lightning to northeastern Illinois, where a flooded viaduct was blamed for an accident that killed a Chicago bus driver.

The storms also caused long delays for travelers.

A lightning strike damaged the signal system along a commuter train line, stalling about 20 trains between Chicago and Auroro for up to two hours during rush hour, Metra spokeswoman Judy Pardonnet said.

And all flights at O'Hare and Midway airports were delayed and many were canceled, said Wendy Abrams, a spokeswoman for Chicago's Department of Aviation.