A bruising storm system raced through the heart of Montgomery County and counties to the east Thursday afternoon, generating at least one tornado and downing trees and power lines.

There were no reports of injuries in the immediate aftermath of the tornado, which touched down near Colesville and Olney. Montgomery fire officials responded to reports of downed trees and wires across the county, with Bethesda, Colesville and Rockville hit the hardest.

“It seemed to come all at once, fast and furious,” said Lynn Steeley, a mother of two in Olney who was working at home when the rain began. Then the phone rang; it was a robo-call saying dismissal at her son’s elementary school would be postponed until the weather cleared.

She had braced for worse. “I was honestly expecting it to rain until 7 tonight,” she said. “It was less severe and shorter than expected.”

Two Montgomery County schools, Sligo Middle School and Blair Ewing Center, were without power Friday morning and will be closed for the day, officials said. All other public schools in the county are open.

District residents captured images of the ominous clouds and fat rain drops that inundated Washington as part of a storm Thursday. (Sarah Parnass/The Washington Post)

Thursday’s storm was but a faint echo of last year’s derecho, one of the most destructive thunderstorms to hit the Washington region in recent memory. That June 29 storm had winds of 60 to 80 mph, uprooted hundreds of trees and left more than 1 million area residents without power.

The storm Thursday carried just a hint of that menace.

Financial adviser Robert Hausman said he took refuge in a stairwell at his 17th-floor office in Rockville shortly before 4 p.m. as the windows shook and the sky darkened. “You could see the Tysons Corner buildings, and then you saw this black cloud and Tysons disappeared under the cloud,” he said. “It was like a smoke cloud. Everything was gone. You could not see out the window.”

During the morning’s first band of thunderstorms, a zoo employee was struck by lightning in northeast Maryland, fire officials said. The 19-year-old woman had been feeding animals at Plumpton Park Zoo in Rising Sun. The woman was taken to a hospital north of Baltimore, and details about her condition were not available.

In West Laurel, at least one home was heavily damaged by a falling tree in the afternoon. Minutes before the storm roared into the Prince George’s County town, Zita Bowley, 85, told her daughter, Yvonne, to get her clothes and other essentials. A newscaster had just reported that a tornado might be headed to their area.

Within minutes, they heard what Susan Sumner, a neighbor, described as a “magnificent crash.” A huge poplar tree had been uprooted and had slammed into the rear of the blue rambler, creating a gaping hole in the bedroom and hallway.

“I’m very thankful,” Bowley said as tears welled in her eyes. “I thought that was it. . . . It is as if the ground shifted beneath my feet, and in a way it has.”

The house, where Bowley has lived for 59 years, is uninhabitable. She and her daughter, who has Down syndrome, were staying Thursday with Sumner. “We’re just fortunate that no one was injured,” Sumner said. “Things can be fixed.”

As police officers and adjusters walked around the property, Lt. David Parker of the Prince George’s police department retrieved World War II medals from Bowley’s bedroom. They were earned by Bowley’s late husband, Joseph.

“She’s very, very lucky,” Parker said. “They were probably about five feet away. . . . The roof is caved in like a V.”

Most of the power outages reported in the region were in Montgomery, where about 7,100 people were still without electricity at 11:30 p.m.

Hours earlier, Pepco linemen Mark McGuire and Ryan Lemay were hunting for the cause of a 350-house outage along Eldwick Way in Potomac.

Lemay went up in the bucket to carefully touch his detector to the 13,000-volt lines, and he found one of the overhead lines was dead. The two would slowly backtrack to the next working transformer until they found the faulty line.

Resident David Erickson said he was happy to hear McGuire’s estimate that power would be restored in an hour.

“I have a generator, but I don’t [want] to start it if I don’t have to,” he said, with darkness coming on. “Everybody hates the noise.”

Rockville resident Patricia Udovich was prepared for the storm. When she and her boys got home from school, the sky got very dark and the wind picked up.

And then, “it just exploded with rain,” Udovich said.

She took her sons into the lower level of their home, and Udovich watched the storm through the window. “It almost looked like clouds were going across my lawn,” Udovich said.

When the storm was over, tree limbs covered her yard, and when the electricity went out, she retreated to a friend’s house for pizza.

Elena Torbenko and Dennis Sanders weren’t as fortunate. They closed on their home on Bauer Drive in Rockville on May 24 and haven’t even moved in yet. On Thursday, the roof was badly damaged when trees fell on both ends of the house. Now, with repairs ahead, they have to wait even longer to move in.

“I knew about this storm,’’ Torbenko said. “I was in one of the bedrooms. I closed all the windows, and I heard a boom, and I ran to hide in the basement.” When the storm passed, she ran to the house of a neighbor, whom she had not yet met.

High winds caused long delays at the region’s three major airports. At Reagan National Airport, the arrival and departure board reflected the impact of the morning storm, with delays and cancellations for destinations ranging from Buffalo to Detroit.

Brian Magee’s 8 a.m. flight out of John F. Kennedy International Airport in New York was delayed two hours, and then the plane flew at 5,000 feet for the entire 55-minute trip, he said. The ride? Incredibly bumpy.

“I’ve never been on a flight like that, and I fly a lot,” said Magee, 27, who is a pilot. “It was rough.’’

And car traffic in the region wasn’t much better as the storm bore down Thursday afternoon.

“On the highway, you could see two to three feet [ahead], tops,” said Anuj Mehta, who was trying to get from his home in Germantown to the shopping center where he works in the Olney area. “I was one of the brave ones to stick it out on the road. I was still an hour late; there were so many downed trees.”

Lori Aratani, Mark Berman, Lynh Bui, Nicole Chavez, Aaron C. Davis, Caitlin Gibson, Steve Hendrix, Justin Jouvenal, Katherine Shaver, Susan Svrluga, Ovetta Wiggins, Clarence Williams and Julie Zauzmer contributed to this report.