At 3:20 p.m., the warning area moved into Baltimore and Baltimore County. The storm was barreling northeast toward Woodlawn, Pikesville and Towson, where schools were about to dismiss for the day.
Officials at three Baltimore County elementaries -- Franklin in Reisterstown, Hillcrest in Catonsville and Wellwood International in Pikesville -- held their children inside until the brunt of the storm passed by.
"They just wanted to be sure they didn't put any buses on the road and in harm's way," said school system spokesman Charles A. Herndon.
No damage was reported at any of the county's more than 160 schools. But hail from 3/4 inch to 1 3/4 inches in diameter was reported in northern Baltimore and White Marsh.
Downtown Baltimore saw brief but torrential rains. Marble-sized hail pelted Bolton Hill and the rains flooded the intersection of Mount Royal and North avenues with about a foot of water.
The storm cell crossed the city and moved up the western shore of the Chesapeake Bay.
A severe thunderstorm warning was issued at 4:35 p.m. for Harford County and northern Maryland as the storm charged on to the northeast at 50 mph.
Instruments at the Aberdeen Proving Ground recorded a wind gust of 47 mph, according to the National Weather Service. One-inch hail was reported at Edgewood.
Cecil County emergency management officials reported half-inch hail and numerous trees toppled in Chesapeake City at 4:35 p.m.
Tornado watches were later issued for southeastern Pennsylvania counties.
More severe thunderstorm warnings were issued for Frederick County last night as a storm moved across the state at 55 mph, with damaging winds as high as 75 mph.
Sun staff writers Johnathon E. Briggs, Stephanie Desmon, Tim Craig, Sheridan Lyons, Jason Song and Julie Bykowicz contributed to this article.