Besides reports of damaging winds and preliminary tornado sightings, the weather service has received reports of hail at least an inch in diameter in locations stretching from southeast Minnesota to Virginia, he said.
In Ohio, storms with swift, straight-line winds soaked parts of the state, knocking down trees and barns and leaving many without power Thursday as commuters dodged fallen branches on roads and faced backups at intersections where traffic lights were out.
Straight-line winds topping 70 mph were reported and more than two dozen tornado warnings were issued as two rounds of storms pummeled the state, but no twisters have been confirmed, said Phillip Johnson, who was part of the team monitoring developments for the Ohio Emergency Management Agency.
Play was suspended at the U.S. Open at Merion Golf Club outside Philadelphia less than two hours after the start of the first round and resumed about three hours later before another brief delay in the evening.
In New Jersey, officials opened the state's Emergency Operations Center on Thursday morning to monitor the storm's progress. The weather service issued a flood watch for most of the state. Forecasters predicted 1 to 2 inches of rain will fall on swollen rivers and streams. As thunderstorms rumbled across the southern and central parts of the state, thousands of residents were left without power.
In northern New York, rain sent rivers and streams over their banks, leading to evacuations and road closures.
Early Thursday morning, thunderstorms that punched through northern Illinois caused significant wind damage, mainly in rural areas west and south of Chicago. The city was largely spared. The weather service said intense winds estimated to have reached 70-80 mph in some areas snapped large trees at their trunks or uprooted them entirely.
Whether the storms were a derecho will take time to determine, forecasters said. A derecho is a storm of strong straight-line winds spanning at least 240 miles. The systems are distinctive and take on a comma or bow shape, and usually have a large area of very cold cloud tops not typically seen in an ordinary thunderstorm.
"A derecho is based more on research," said Evan Bentley, a meteorologist at the weather service office for northern Indiana. "How much damage, how widespread it was." It could take days to determine whether the storms met the criteria, he said.
Even if the storm wasn't a derecho, it still brought several tornadoes, large hail and flooding that did some damage Wednesday.
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 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.
Nearly a year ago, a derecho led to two dozen deaths, caused at least $1 billion in damage from Chicago to Washington, and left more than 4 million customers without power. Winds reached nearly 100 mph in some places.
Associated Press writers David Dishneau in Baltimore; Sarah Brumfield and Seth Borenstein in Washington; Bob Lewis in Richmond; Carla K. Johnson in Chicago; Malcolm Ritter in New York; Charles Wilson in Indianapolis; and Barbara Rodriguez in Des Moines, Iowa contributed to this report.