DES MOINES, Iowa — Baseball-sized hail pummeled homes and cars in Nebraska and Iowa on Tuesday as powerful thunderstorms moved through a swath of Midwest states, also causing severe flooding and prompting reports of tornadoes.

The National Weather Service said reports of extensive hail damage and flooding trickled in as storms pushed into Nebraska and moved into neighboring Iowa, where winds of up to 85 mph were recorded. Up to 4 inches of rain was expected in parts those states, which were the hardest hit. The storm also tracked across parts of Kansas, Missouri, South Dakota and Illinois.

“This is one of these days we can’t let our guard down,” said Bill Bunting, forecast operations chief at the Storm Prediction Center in Norman, Oklahoma.

Bunting said several trained spotters reported tornadoes in central and southwest Iowa, and at least one report came in from southwest Kansas. Reports will not be confirmed until damage can be assessed Wednesday morning.

Becky Kern, a meteorologist with the National Weather Service in Valley, Nebraska, said the system has involved a “training” of thunderstorms, which involves a series of thunderstorms following one after another.