Luis Rosa, a National Weather Service meteorologist, said Friday that the heaviest rainfall was over Bel Air, which received nearly 5 inches.
He said 3 to 4 inches fell in areas such as Fallston, Darlington, Hickory and Pleasant Hill.
Rosa said radar images at the NWS' Baltimore-Washington Forecast Office in Sterling, Va. showed much of the rain falling north of I-95 between Fallston and the east bank of the Susquehanna River.
"It was a localized event, really," he said. "Baltimore County didn't have that much rain compared to Harford County.
Rosa reported several road closures caused by flash flooding, including Route 543 and Chestnut Hill Road in Hickory, Winters Run Road and Singer Road north of Joppa and East Wheel Road and Patterson Mill Road south of Bel Air.