Strong winds and hail battered a swath of states through the Ohio Valley overnight, damaging cars, homes, knocking over trees and power lines, and spawning at least one tornado.
Tennessee and Pennsylvania appeared to bear the brunt of the bad weather, with reports of tornadoes in both states. But the storm hit portions of at least eight states, also including Indiana, Ohio, Kentucky, West Virginia, Virginia and North Carolina, according to a National Weather Service map.
The storm can be blamed on a competing mix of warm and cool temperatures across the Ohio Valley, said Paul Walker, senior meteorologist with AccuWeather.
"There was cold air clashing with the warm air, causing the atmosphere to be very unstable," he said.
A tornado touched down in southwestern Pennsylvania on Wednesday night, severely damaging dozens of homes and a high school auditorium where students were rehearsing a play, said Kurt Ferguson, manager of Westmoreland County's Hempfield Township.
About 40 houses in the area have been deemed uninhabitable, based on an initial damage assessment, he said. Some were essentially "blown apart," while others were badly damaged.
No serious injuries have been reported due to the tornado, which touched down shortly before 6 p.m. local time, according to Ferguson. The Red Cross has set up shelters, and the township plans to send emergency workers into the tornado-hit areas with food.
On one road, as many as 50 trees had been uprooted and power lines had fallen, Ferguson said.
"We couldn't even get to all the areas affected," he said.
About 100 students were rehearsing a play in an auditorium at Hempfield Area High School when the tornado struck, ripping off part of the roof, he said. They were evacuated from the building safely, Ferguson said.
Lee Hendricks, a meteorologist with the National Weather Service in Pittsburgh, said the service had dispatched a team to the area to assess the damage.
"At this point it appears it was a tornado," he said, though details such as its intensity and path have not yet been determined.
In Tennessee, there were reports of roof damage, broken car windows and a barn blown down east of Nashville.