Massive storm system that battered Midwest surges toward Mid-Atlantic CHICAGO - A massive line of storms packing hail, lightning and tree-toppling winds began rolling through the Midwest Wednesday evening and could affect more than one in five Americans from Iowa to Maryland before subsiding. In the small town of Belmond, Iowa, about 90 miles north of Des Moines, Duwayne Abel, owner of Cattleman's Steaks Provisions restaurant, said a tornado swooped through his business' parking lot and demolished part of the building. No one was in the restaurant at the time. "I was, oh, eight miles west of town and I looked toward town and I could see a funnel cloud, having no idea it was exactly where our restaurant was," Abel said. His wife and an employee were able to get out of the restaurant and sought shelter in a basement. Other small tornadoes were also reported in other parts of Iowa and in Illinois. More than 1,200 customers in northern Iowa have lost power. In addition to tornadoes, lightning and large hail, meteorologists were 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 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. Flash flooding was also a concern in some areas. 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 and a symphony concert at the city's downtown Millennium Park was canceled. The Metra commuter rail service halted all inbound and outbound trains, and Northwestern University canceled classes and finals at its campuses in Chicago and suburban Evanston. Airlines canceled more than 120 flights at O'Hare International Airport. The warnings prompted the Northern Indiana Public Service Co. to increase staff at its customer call center and scheduling extra work crews to handle any power outages. Pennsylvania Emergency Management Agency spokesman Cory Angell said a standby worker was added at the emergency operations center in Harrisburg and officials had ensured two National Guard helicopters were ready if needed for water rescues. All told, the area the weather service considered to be under heightened risk of dangerous weather included 74.7 million people in 19 states. Winds reached nearly 100 mph in some places and in addition to the 13 people who died from downed trees, an additional 34 people died from the heat wave that followed in areas without power. Tornadoes and a derecho can happen at the same time. Straight-line winds lack the rotation that twisters have, but they can still cause considerable damage as they blow down trees and other objects. The term derecho was coined in 1888, said Ken Pryor, a research meteorologist at the Center for Satellite Applications and Research at the National Oceanic and Atmospheric Administration in College Park, Md. The word is Spanish for "straight ahead" or "direct," Pryor said. The structure of a derecho-producing storm looks distinctive in radar and satellite imagery, Pryor said. "The systems are very large and have signatures that are very extreme," he said. You get large areas of very cold cloud tops that you typically wouldn't see with an ordinary thunderstorm complex. The storms take on a comma or a bow shape that's very distinctive.