The storm roared into the area around 6 p.m., cutting a swath through the Halfway and Wesel boulevards-area to Hagerstown's West and North Ends.
Some of the hardest hit areas were Carroll Heights, Haven Road and Outer Drive, Hagerstown Fire Chief Gary Hawbaker said.
Officials in Berkeley and Jefferson counties in West Virginia reported severe damage in some areas.
A tornado warning had been issued for Jefferson County and Washington County before the storm hit.
The National Weather Service received unconfirmed reports of tornadoes touching down in the southwestern portion of Jefferson County and western Shepherdstown, said meteorologist Dewey Walston.
Authorities in the Shepherdstown area said that area had not sustained serious storm damage.
Severe lightning struck just feet from a Martinsburg, W.Va., home, blowing mud through the siding and lawn chairs off the porch.
'Like a bomb'
"It was like a bomb went off," said Janice Hayes, of 2102 Street of Dreams, surveying the damage the lightning caused. "Everything in the back of the house was blown out. Medicine from the medicine cabinet was blown onto the floor."
Lightning apparently hit the trunk of a tree in the back yard shortly after the heavy rains ended at around 7:30 p.m. The force yanked plants out of the ground, hurtled mud at the back of the home hard enough to leave holes and blew out electrical appliances.
Berkeley County Emergency Services reported a tree had fallen on a home, a transformer fire and a field on fire shortly after 6 p.m.
Fire companies and the West Virginia Division of Highways in Martinsburg reported trees down throughout the county.
The storm grazed the southern portion of Franklin County, but only minor damage was reported in Waynesboro, Pa.
Shoppers were evacuated from Valley Mall in Hagerstown as strong winds took off portions of the roof and smashed at least one window.
It was unclear Tuesday night whether the mall would be open today.
A commuter flight from Pittsburgh that was to land at Washington County Airport at about the time the storm hit was sent to another airport, said Airport Manager Carolyn Motz.
It was still sunny when Jake-the-dog ran into the shed behind his owner's Columbia Road house in Hagerstown. Jake developed an uncanny ability to predict storms when his doghouse was overturned in a storm several years ago, and now he hightails it into the shed at the first sign of one, said his owner Sharon Kronawetter.
"I saw the tail end of him go into the shed, and I said, 'God, it's coming,'" Kronawetter said.
Soon afterward, a 60-foot tree landed on her house.
By the time the storm ended, the back fence was flattened and the porch was damaged, she said.
"We can't even get out our back door," Kronawetter said.
Firefighters, rescuers and police, along with telephone, electric and cable television crews worked into the night responding to storm-related emergency calls.
Some cars were trapped briefly at intersections when the storm flooded some streets, Hawbaker said.
The northbound lane of Interstate 81 was shut down for a few minutes across from the Washington County Detention Center when a tree fell, blocking a portion of the right lane, according to Maryland State Police.
Virginia Avenue from Halfway Boulevard to Governor Lane Boulevard was also closed, among other roads throughout the area, police said.
Staff Writers Don Aines, Steven T. Dennis, Julie E. Greene, Sheila Hotchkin, and Amy Wallauer contributed to this story.