CHICAGO (AP) - An unusually massive line of storms packing hail, lightning and tree-toppling winds was rolling through the Midwest on Wednesday and could affect more than one in five Americans from Iowa to Maryland.
Meteorologists were even warning about the possibility of a weather event called a derecho, which is a storm of strong straight-line winds spanning at least 240 miles. The storms are also likely to generate tornadoes and cause power outages that will be followed by oppressive heat, said Russell Schneider, director of the National Weather Service's Storm Prediction Center in Norman, Okla.
The weather service said two tornadoes touched down in northern Iowa late Wednesday afternoon. In Illinois, emergency officials in Winnebago County reported several small tornadoes touched down briefly. No damage was reported.
For the first time this year, the center was using its highest alert level for parts of Iowa, Illinois, Indiana and Ohio. In Chicago, Wednesday night's White Sox game against the Toronto Blue Jays was postponed in anticipation of bad weather and airlines canceled more than 120 flights at O'Hare International Airport.
Northwestern University canceled classes and finals scheduled for Wednesday night on its Chicago and Evanston campuses, and a symphony concert at the city's downtown Millennium Park was also canceled. The Metra commuter rail service announced on its website that it had halted all inbound and outbound trains from Chicago because of the storm.
The storms were expected to push into northwest Indiana later. The Northern Indiana Public Service Co., the region's largest utility, said it was increasing staff at its customer call center and scheduling extra work crews to handle any outages.
Tornadoes and a derecho can happen at the same time, but at any given place Wednesday the straight-line winds are probably more likely. Straight-line winds lack the rotation that twisters have, but they can still cause considerable damage as they blow down trees and other objects.