The Washington, D.C., area was being hit by storms and the National Weather Service issued severe thunderstorm watches and warnings for much of the region. Forecasters warned that the storms could produce damaging winds and large hail, and the the threat would run into at least early evening Thursday. A flash flood watch was in effect.
In Maryland and Delaware, officials reported trees down, roads closed, and tens of thousands of power outages after a line of heavy thunderstorms moved through. In the afternoon, the weather service said a tornado was reported near Colesville or Olney, just north of Washington, but there have been no reports of serious damage.
Federal agencies in the area were open but workers were allowed to take unscheduled leave or work from home. In Delaware, thousands were without power, and a 19-year-old woman who works at Plumpton Park Zoo in Rising Sun, Md., was struck by lightning and sent to the hospital.
Lightning from a fast-moving storm may have sparked a fire that killed a western Pennsylvania man early Thursday, the state fire marshal said. The fire happened in New Brighton, about 25 miles northwest of Pittsburgh.
In southern West Virginia, the Roane County 911 center has been evacuated and roads in the Spencer area were closed because of flash flooding.
Still, overall, the storms appear to have caused less wind damage than was feared through early Thursday, said Bill Bunting of the National Weather Service's Storm Prediction Center in Norman, Okla. Whether they were as bad as anticipated "depends on where you live," he said.
He said thunderstorms took longer than expected to merge into a large line that could cause widespread damage. The merger also happened farther east than expected, which limited the potential for widespread damage in Illinois and Indiana, though those states still had pockets of severe weather.
Even before merging, the individual storms remained powerful, Bunting said.
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.
And morning rush-hour commuters tried to get to work through torrential downpours and dark skies that made it look like nighttime.
In New Jersey, officials opened the soaked 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.
Overnight, 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.
By early Thursday, though, the derecho that had been forecast hadn't developed.
"With each hour that goes by, it's less likely," said Greg Carbin of the storm prediction center.
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.
While the Midwest dodged a derecho, several tornadoes, large hail and flooding 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.
Last year, a derecho caused at least $1 billion in damage from Chicago to Washington, killing 13 people and leaving more than 4 million people without power, according to the weather service. Winds reached nearly 100 mph in some places. In addition to the people killed in the storm, 34 more died from the heat wave that followed in areas without power.
Associated Press writers Carla K. Johnson in Chicago; Malcolm Ritter in New York; Charles Wilson in Indianapolis; Barbara Rodriguez in Des Moines, Iowa; and Seth Borenstein in Washington, D.C., contributed to this report.