PITTSBURGH -- A pair of storms that pounded Pittsburgh on Friday cut electricity to hospitals and universities and submerged more than a dozen vehicles in a flash flood that killed a woman and two children and left another person missing and presumed dead.

Officials said drivers were overwhelmed as water rose up to 9 feet in some places along Washington Boulevard, a main road that parallels the Allegheny River in the city's Highland Park section.

The area received 2.1 inches of rain in an hour, said Rihaan Gangat, a meteorologist for the National Weather Service. But an earlier storm meant the region was drenched by 3 to 4 inches of rain overall Friday.

The three victims, whose names were not released, were unable to escape their vehicle, which was completely submerged and pinned to a tree, Pittsburgh public safety director Michael Huss said at a news conference.

Rescuers floated over the car without knowing it was below.

"The bottom of the boat didn't even scrape against the top of the car," said Raymond DeMichiei, deputy director of the city Office of Emergency Management.

A fourth person, a 70-year-old woman, was missing and presumed dead, police chief Nate Harper said.

Harper said 18 vehicles were stranded in the high water and 11 people were rescued. One of the rescued women required hospital treatment.

The water had receded by Friday evening, but the mud-caked road will remain closed through Saturday as emergency crews work to clear all the stranded cars.

Tara Howes, 34, of Gibsonia, told the Tribune-Review that "manhole covers started popping up and it looked like the road exploded and the waters came up really fast. I saw people swimming on the sides of the road. It was pretty scary."

The flash floods hit an area that experienced serious flooding last month. Washington Boulevard is situated in a valley. Rushing water from a July 18 storm stranded motorists and caused a section of the road to buckle.

Claudia Gallagher, 55, of West Mifflin, was driving north on Washington Boulevard at the height of the rainfall Friday and tried to get off the road as the water rose.

"We tried to drive up onto the curb, but the water had other ideas," she told the Post-Gazette.

Her car began to float, and she opened her window and climbed onto the roof. Many other drivers nearby were sitting atop their cars, too, she said.

Earlier Friday, another storm caused power outages that led the University of Pittsburgh to close for the day. Parts of Carlow and Carnegie Mellon universities also lost electricity.

Flights at Pittsburgh International Airport were grounded because of lightning just after 3 p.m., spokeswoman JoAnn Jenny said.

Two hospitals operated on emergency power after rains flooded a substation in the city's Oakland neighborhood.