The damage from the storm included two collapsed buildings in Baltimore and a police cruiser that was crushed under a tree limb.

About 11:45 p.m., a tree fell on a police vehicle in the 4600 block of Charles St. The female officer was taken to a nearby medical center and is in good condition, police said. A second officer was struck in the arm and also taken for treatment.

Sgt. Anthony Smith said a three-story building at 1901 E. 31st St., the site of a construction zone, collapsed, as well as a three-story vacant building at 1934 Wilkens Ave. Smith said the areas are closed to pedestrian traffic; no injuries were reported.

Alessandro Vitale witnessed a tractor-trailer accident on the Bay Bridge late Friday as winds approached 80 mph. Vitale watched the accident through his windshield as he was driving east across the bridge, shortly after winds shook his own Ford F350 truck side to side near the middle of the span.

"All of a sudden I felt my truck moving," he said by phone. "I look to my right. There is a tractor-trailer that starts swaying. I slow down and watch this tractor-trailer completely get knocked over."

"It's resting on the concrete barrier — almost falling off the bridge," he said.

Vitale, who runs business operations at the Harbor East restaurant Chazz: A Bronx Original, was driving to Ocean City. The driver of the tractor-trailer suffered non-life-threatening injuries and was taken to a nearby hospital, according to Sgt. Kirk Perez of the Maryland Transportation Authority Police.

Officials were prepared to close the Bay Bridge if any storms Saturday night were severe.

Ken Mallette, director of Maryland Emergency Management Agency, said residents should use extreme caution when driving. Traffic lights across the state are out because of power outages, he said. Drivers should also be alert for downed wires and first responders and utility crews working on the roadsides.

Meanwhile, three Baltimore City fire companies that had been slated to permanently close Sunday will remain open for four more days due to the weather, said department spokesman Chief Kevin Cartwright. Fire officials have decided to keep the three companies open until Thursday morning to help clean up from the storm and aid those suffering from heat-related health problems, he said.

Firefighters have been helping with downed wires and caring for people afflicted with heat exhaustion or heat stroke — particularly elderly and home-bound people who have lost power, Cartwright said.

Three companies — East Baltimore's Truck 15, West Baltimore's Truck 10 and Southeast Baltimore's Engine 11 — had been set to close Sunday morning as a cost-cutting measure.

The closures have been postponed until 7 a.m. Thursday, Cartwright said.

In Northwest Baltimore and Baltimore County, residents were asked to conserve water as tanks were expected to refill overnight after a loss of power at pumping stations. That resulted in areas, including Reisterstown and Owings Mills, being without water.

Baltimore residents are asked to continue to conserve water during the heat wave so it is available for vital services, such as hospitals and senior citizen complexes. To help, residents could defer household chores, such as laundry and dishes, until evening hours.

Francie and Jared Spahn said they feel lucky, even though a huge sugar maple tree limb fell on their Guilford home, near their son's bedroom around midnight Saturday.

"It looked like daylight outside; there was so much lightning," Francie Spahn said. "And the thunder was so strong, it was rattling the windows.

"And then I hear something crunch, and Jared comes and gets me and goes, 'Don't scream or you'll wake the kids, but come here and look at something.' It hit every window or glass door that we have, and we were just very thankful that nothing shattered. It could have been much worse. We were one of the lucky ones."

Baltimore Sun reporters Childs Walker, Scott Calvert, Andy Rosen, Julie Scharper and Jessica Anderson and Reuters contributed to this article.