CHICAGO (AP) — The National Weather Service is upgrading the risk of storms to its highest alert level for parts of Iowa, Illinois, Indiana and Ohio.

The agency's Storm Prediction Center in Norman, Okla., says there's a high risk that damaging winds will strike in extreme eastern Iowa into northern portions of Illinois and Indiana and northwest portions of Ohio.

Storm Prediction Center Director Russell Schneider says it's the first time this year that the center has used its highest alert level. Wednesday's storms are likely to generate tornadoes and cause power outages.

The storms could affect more than one in five Americans on Wednesday as they rumble from Iowa to Maryland packing hail, lightning and tree-toppling winds.

Schneider says the storm could hit Chicago around rush hour.