Kimberly Griffith, 45, of Plum, Penn., and her daughters, Brenna, 12, and Mikaela, 8, became trapped in their car as the water rose to as high as 9 feet in some places, The Pittsburgh Tribune-Review reported.
"The bottom of the boat didn't even scrape against the top of the car," Raymond DeMichiei, deputy director of the city Office of Emergency Management, told the Associated Press.
Rescuers lob a life vest to Bob Bailey, 79, who climbed on the roof of his car after being caught in a flash flood (Chris Langer/AP)
A pair of storms drenched the Pittsburgh region with more than 4 inches of rain on Friday, sending floodwaters surging through Washington Boulevard near its intersection with Allegheny River Boulevard.
Police said 18 cars were trapped in the flooding and 11 people were rescued. The water pinned their vehicle to a tree and they were unable to escape, authorities said earlier.
Rescue workers also recovered a body from the Allegheny River believed to be that of an older woman reported missing during the flood, Raymond DeMichiei, the city's deputy director of emergency management, said on Saturday.
During the flood, more than a dozen cars were stranded along the road, local media reports said, and paramedics in boats went from car to car to rescue drivers and passengers. Flash floods submerged more than a dozen vehicles in Pittsburgh, killing killed two women and two children, and forcing others to swim to safety or scramble onto the roofs of their cars.
Suddenly, in the Highland Park section water started rising.
Within minutes, Washington Boulevard was a nine-foot-deep raging river - a river with 18 cars in it, reports CBS News correspondent Dave Browde.
"Water was rushing so fast, it kind of just dragged me right out," one woman said. 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.
Rescuers intent on rescuing a man from a tree floated over the car without knowing it was below.
Police Chief Nate Harper said 18 vehicles were stranded in the high water and 11 people were rescued. One woman required hospital treatment.
People were clinging to trees, poles and car roofs, KDKA-TV reported. The water receded Friday evening, but the mud-caked road remained closed Saturday as emergency crews work to clear the stranded cars.
The flash floods hit an area that saw serious flooding last month. Rushing water from a July 18 storm stranded motorists and caused a section of Washington Boulevard to buckle.
DeMichiei said emergency officials will discuss steps to avoid future tragedies from flooding at the site.