Strong thunderstorms that swept across metro Atlanta Thursday evening downed trees and sparked several house fires, and forecasters are warning of another round of potentially severe storms later today.

The National Weather Service has issued a severe thundestorm watch for 28 northwest Georgia counties, including Bartow, Carroll, Cherokee, Clayton, Cobb, Coweta, Douglas, Fayette and Fulton counties in metro Atlanta.

The watch, which means conditions will be favorable for the development of severe storms, is in effect until 8 p.m.

At 1:30 p.m., weather radar showed a large area of strong storms moving into the northwest corner of the state, with smaller storms popping up across Cobb and Paulding counties.

In Gwinnett County, firefighters were busy battling three house fires between 9 and 10 p.m. that were caused by lightning, according to Gwinnett fire Capt. Tommy Rutledge. The storms also brought trees down onto utility lines and roadways in several areas, Rutledge said.

In southwest Atlanta, one of several downed trees crashed through the roof of Rodney and Dorothy Holmes’ house on Laurelmont Drive.

“I was on my PC and playing with my dogs, and I heard this loud popping and cracking sound,” Rodney Holmes told The Atlanta Journal-Constitution. “Next thing I know, I heard the tree fall.”

He said the tree, an oak more than 100 years old, split in half. One side crashed onto the house he has lived in since 1970 and the other half fell onto power lines and into the road.

Trees were also reported down in Forsyth, Polk, Gordon and Floyd counties, according to the National Weather Service. Hail 1.5 inches in diameter was reported in Baldwin County in middle Georgia.

In downtown Atlanta, Forsyth Street was closed from Martin Luther King Jr. Drive to Alabama Street Friday morning while crews worked to repair storm damage at the Nunn Federal Building, according to Atlanta police spokeswoman Kim Jones.

The storm apparently loosened architectural panels on the underside of a pedestrian bridge across Forsyth Street.

The Weather Service said damaging straight-line winds and frequent lightning will be the main threats as another round of thunderstorms fires up across metro Atlanta later today.

“The showers and storms will start to fire up around 3 o’clock and on into the evening hours,” Channel 2 meteorologist Karen Minton said. “They’ll be with us through the afternoon rush hour.”

The chance of rain later today is 40 percent, and that pattern will continue into the weekend, Minton said.

She put the chance of rain at 30 percent Saturday, 40 percent Sunday and 30 percent Monday and Tuesday.

Highs through the weekend will top out in the upper 80s, with morning lows around 70 degrees.