A torrential rainstorm thrashed the Washington area yesterday, spawning swirling floods that submerged dozens of area roads, closed Prince William schools early and contributed to the death of a woman crossing an intersection, authorities said.

So much rain fell between 7 a.m. and noon yesterday that the Potomac River swelled to about 10 times its average flow for October and Dulles International Airport collected about as much rain -- three inches -- as it normally would all month.

The worst of the rain was concentrated in Fairfax and Prince William counties. In Montgomery County, police closed 13 roads, most of which were in Gaithersburg and Rockville. Loudoun County closed 10 roads, mostly in the rural western end, because of flooding.

It was the second straight week that a major storm made life miserable for area commuters. Last week's windstorms hit late in the afternoon, felling trees and making the evening rush hour even more wearing than usual. Yesterday's storm began pouring down in the morning, snarling many of Northern Virginia's curving two-lane roads.

Fairfax County, where 32 roads were closed and 18 others were inundated in at least six inches of water, was particularly hard hit. Commuters cursed at officers who prevented them from entering flooded streets, police said, and in some cases the most stubborn commuters ignored police warnings altogether.

"There were three cars where people decided to go around the barricades we set up and were swept off the road," said Capt. Ron Miner, commander of the Traffic Division for Fairfax police. "We told them it was too deep and they said, 'Oh, I think I can make it.' "

All were able to leave their cars without injury, Miner said.

Flooding also sealed off the entrance to a small business area near Alexandria, forcing police to escort about 50 people past six-foot floodwaters, through woods and up an embankment to the Capital Beltway near Van Dorn Street yesterday afternoon. There, they were loaded onto two buses and a van to take them to their cars.

"It's disgusting," said J.D. Blevins, a 60-year-old mechanic, as he surveyed a freshly formed pond that blocked him from getting to his job yesterday afternoon. "I was supposed to work tonight . . . . It's a pain."

"Usually when it's this bad, it's been a hurricane or tropical storm," said Suzanne Malone, looking over a small lake that once was Woodburn Road in Fairfax County. The water had poured over the banks of Accotink Creek, submerging shrubs, toppling traffic signs and flooding nearby Prosperity Avenue.

According to the National Weather Service, Malone's analysis was correct. Yesterday's bullet-hard rainfall was "the caliber of rain you'd get with a tropical system," said Edwin Danaher, a Weather Service forecaster.

Danaher said the downpour was similar to that of tropical storm Marco, which pelted mountainous western Virginia with about four inches of rain last week.

"This was not really a tropical system," Danaher said. "It's the sort of thing you'd actually see every couple of years."

"All the conditions for heavy rain fell into place" yesterday, Danaher said. He said a slow-moving cold front drifting east over the mountains and easterly winds off the ocean brought moisture. He said a low-pressure system at higher levels in the atmosphere "brought in enough energy to produce all this rain."

In Prince William County, the school system's 42,000 students were sent home two hours early because of concern that school buses leaving later would be unable to traverse some of the more than 12 roads in the county made impassable by flooding.

Elizabeth Robins was hit and killed about 6 a.m. as she walked across an intersection in Woodbridge, said Prince William County police spokeswoman Kim D. Chinn. Chinn said weather is believed to have been a factor in the accident, which remains under investigation. "It was 6 a.m., it was dark, raining, visibility was probably bad," she said, adding that no charges have been filed against the motorist.

One lane of Interstate 66 was flooded near Arlington, and Virginia State Police reported 26 accidents on the four local interstates and the toll road, including one in which a man was injured when his Suzuki Samurai hydroplaned and overturned on the outer loop of the Beltway south of Braddock Road, according to Lucy Caldwell, State Police spokeswoman.

"The drainpipes in Northern Virginia simply aren't built to handle the type of rain we've been having since 4 this morning," said Mary Anne Reynolds, regional spokeswoman for the Virginia Department of Transportation.

She said work crews were out at 7 a.m. yesterday throughout Northern Virginia, trying to pump water off the roads. "In some cases, the pumps couldn't keep up with the rain," Reynolds said.

The storm also forced many District commuters to take unaccustomed routes home after sporadic flooding closed Beach Drive about 5 p.m. Rock Creek itself, fed by the daylong rains, continued to rise through the afternoon and early evening, and some lanes were shut along Rock Creek Parkway.

The heavy rains knocked out power briefly at Metro's Foggy Bottom station during the afternoon, affecting elevators and escalators. Service was not affected, and auxiliary power provided lighting to the station until full power was restored, a spokeswoman said.

As of 2 p.m. yesteray, rainfall at Dulles International Airport was 2.92 inches compared with the 3.01 inches that is average for all of October, Danaher said. About 1.15 inches of rain fell at Washington National Airport, compared with the normal rainfall of 2.9 inches in October.

Despite the heavy rain, this year has been only slightly wetter than normal. Since January, 33.94 inches of rain fell at National Airport, 1.66 inches above normal, the Weather Service said.

The forecast for today is for partly sunny skies and temperatures in the low 70s, Danaher said.

Staff writers Gabriel Escobar, Veronica T. Jennings, Maria Koklanaris, Pierre Thomas, Avis Thomas-Lester and Michael Ybarra contributed to this report.