Southern California's weather turned from dangerously dry to dangerously wet Friday as a traffic-snarling rainstorm brought the threat of mudslides and flash floods in areas burned by recent wildfires, triggering evacuations in two fire-scarred canyons.

Residents were ordered to leave 200 homes in Orange County's Modjeska and Williams canyons, while voluntary evacuations were urged in Silverado Canyon, said Battalion Chief Kris Concepcion of the county Fire Authority.

The two mandatory evacuation orders were lifted by 9 p.m. Friday night.

The National Weather Service said that some flash-flooding and debris flows were reported in the Modjeska Canyon area at midafternoon.

Authorities were also watching nearby Trabuco Canyon but had not issued any orders there, Concepcion said.

Sheriff's deputies went door-to-door to alert residents to the risk and an emergency shelter was set up at an area high school.

Flash flood warnings and watches were issued throughout Southern California, where wildfires have stripped vegetation from thousands of acres of land, leaving it susceptible to excessive runoff and erosion.

In north-central San Diego County, more than 2 inches of rain fell in the vicinity of vast areas burned by the Poomacha and Rice wildfires of late October, the weather service said, prompting a flash flood warning late Friday.

Firefighters and residents also kept an eye on Malibu, where the most recent blaze fanned by powerful, dry Santa Ana winds scorched 4,900 acres on slopes and in canyons of the Santa Monica Mountains.

The rain was expected to clear out overnight.

Downtown Los Angeles had a half-inch of rain by evening -- not much by normal standards but relatively significant in the course of the West's long dry spell. Just 3.21 inches were recorded there in the rain-year that ended June 30. Average annual rainfall is 15.14 inches

The rain also turned commuting into a mess, with numerous traffic accidents on rainy roads.

A tractor-trailer rig went out of control before dawn on Interstate 5 in Orange County and all lanes were blocked for hours as firefighters worked to rescue the driver of a pickup truck that became wedged under the trailer. Traffic backed up for miles on the major route.

In San Diego County, a vehicle ran off Interstate 8 and landed upside down, killing one woman and injuring two people, authorities said.

The California Highway Patrol said there were 283 accidents in the San Diego area between midnight and 4 p.m., compared to 50 to 75 on a normal day.

"It is probably one of the worst commutes I've seen in a very, very long time," CHP Officer Alicia Contreras told the San Diego Union-Tribune.

Authorities were also investigating a fatal accident in Duarte, east of Los Angeles, in which a vehicle skidded off Interstate 605 and overturned in a ravine. The driver died at the scene, said Los Angeles County fire Inspector Sam Padilla.

High in the San Bernardino Mountains east of Los Angeles, Highway 18 was shut down between Arrowbear Lake and Big Bear Lake after rocks slid down slopes and hit the road.