Powerful Storm Triggers Floods : Weather: Helicopter rescue crews pluck stranded, terrified drivers from car roofs and treetops. Mudslides and lightning strikes add to the problems.

A powerful Pacific storm pounded Southern California on Monday, triggering mudslides and floods that stranded motorists and forced helicopter rescue crews to pluck terrorized drivers from car roofs and treetops.

The deluge caused the swollen Los Angeles River to overflow in the Sepulveda Dam Basin in Van Nuys, sending a torrent of water onto Burbank Boulevard and nearly submerging dozens of vehicles.

Rescue crews launched rubber boats to save several people who had scrambled up trees to escape their flooded cars while Fire Department helicopters used winches to rescue other stranded motorists. Dramatic television footage showed a helicopter hoisting out two people, and then one of them falling back into the water below.

“We’ve got some major problems out here,” Sgt. Gary Thornton of the Los Angeles County Sheriff’s Department said shortly after heavy rains began to fall in the early afternoon.

The rescue efforts were further hampered by lightning strikes that knocked out power to more than 100,000 residents in Los Angeles County, according to Department of Water and Power officials.

Downed wires and mudslides and rockslides were reported in Malibu and the west San Fernando Valley, where numerous residents in Westlake Village and Agoura Hills reported homes flooded by the downpour.

The deluge caused major commuting headaches and nearly enveloped some smaller vehicles during the evening rush hour. Flooding forced the closure of the Ventura Freeway at the Interstate 405 interchange and California Highway Patrol closed the southbound I-5 at the Hollywood Freeway as well as the 210 Freeway near La Tuna Canyon.

Heavy snow forced the closure of the Grapevine along I-5 for several hours. The CHP closed the highway shortly before noon but the lanes were reopened about 3 p.m. Snow was dusting the mountains at the 4,000-foot level.

Sudden flooding forced national park rangers to close a film production set at Paramount Ranch in Agoura Hills. The film crew had to backtrack around Mulholland Drive to get to safety.

“All of a sudden a ton of water came up the creek and the rangers told us we had to leave for our own safety,” said Tim Johnson, an associate producer with the Sullivan Co. “Things like that don’t happen too often here.”

Although the rain was expected to taper off by today, weather officials said another storm is due to blanket Southern California by Wednesday, bringing with it several more inches of rain. Scattered heavy showers are expected to last throughout the week, according to forecasters.

“Skiers are going to be loving this weather but it’s not going to be good for commuters for the rest of the week,” said Marty McKewon, a meteorologist with WeatherData Inc., which provides forecasts for The Times. “This is a major storm and it’s going to be sticking around for a while.”

Monday’s downpour brought more than three inches of rain in some areas, but even continued rainfall will have little effect on the drought, officials said. Monday’s rains dropped up to a foot of snow in the Sierra, but state water officials said it would take nearly three inches of rain a week for the next two months to bring an end to the water shortage.

“It would take a tremendous, unusual event to pull us out,” said Dee Davis, a spokesman with the state Department of Water Resources Drought Center.

Drought conditions were not on the minds of commuters, who had to cope with flash floods and treacherous road conditions throughout the Southland.

A Los Angeles Fire Department spokesman said a van overturned in Santa Clarita near Soledad Canyon and Bouquet Canyon boulevards, but that everyone in it had been accounted for, despite earlier reports that a woman had been swept away by raging water.

Burbank police declared all major arteries leading to the Burbank-Glendale Airport impassable about 2 p.m. because of heavy flooding. Department spokesman Sgt. Don Goldberg said that several residents reported collapsed roofs because of the downpour.

The drama in the Sepulveda Dam Basin unfolded at Woodley Avenue and Burbank Boulevard, just a few hundred yards west of the San Diego Freeway, about 1 p.m.

John Mittendorf, a battalion fire chief, told reporters that when the river went outside its banks, “numerous people were suddenly caught . . . in their cars.” He said firefighters who tried to rescue them from the ground also were trapped, forcing helicopter teams into action.

County firefighters used ropes to rescue stranded motorists whose vehicles were nearly submerged by water on Sand Canyon Road in the Santa Clarita Valley, and officials eventually closed a four-mile stretch of the low-lying road lined by small ranches, said Inspector Robert Lockett of the Los Angeles County Fire Department.

“They saw the road was flooded and figured they could get by anyway, but they learned their lesson,” Lockett said of the motorists.

More than six miles of streets, including parts of Sand Canyon, Placerita Canyon and Newhall Ranch roads, were closed by midafternoon in Santa Clarita because of flooding, authorities said.

Officials said the roads would be reopened to allow only residents to make their way home once the rain let up.

Topanga Canyon Boulevard was shut down and declared impassable about 2 p.m. because of rockslides and mudslides and flooding, authorities said.

Lightning and rain knocked out power in several parts of the county. About 80,000 DWP customers in the northeastern San Fernando Valley lost power about 2 p.m. when lightning struck a generating station at 9430 San Fernando Road.

The Daily News newspaper and several other companies clustered in Warner Center in Woodland Hills, including Kaiser Foundation Hospital and Litton Industries, lost electricity about 11:30 a.m. when lightning struck a high-voltage power line in the area.

Power was restored within an hour to all but the Daily News, whose electrical wiring was directly hit, said Dorothy Jensen, a DWP spokeswoman.

Flooding problems also forced California State University, Northridge, and Pierce College in Woodland Hills to close for the day. Five branches of the Los Angeles Library in the San Fernando Valley were closed by midafternoon because of flooding and power outages, said spokesman Bob Reagan. The branches were in Sun Valley, Panorama City, North Hollywood, Pacoima and Sunland-Tujunga.

In Malibu, a woman and her two small children narrowly escaped disaster when their car stalled while crossing a rain-swollen creek in an exclusive area of Malibu.

Lisa Hilton, 35, her son, Christian, 4, and her 4-month-old daughter, Fiona, managed, with the help of a neighbor, to get out of the car seconds before the surging water swept their BMW sedan half a mile downstream, where it was submerged in six feet of water, eyewitnesses said.

“The car was like a boat going down the creek,” said actor Nick Nolte, who, along with Frank Capra Jr., was among the first people to arrive at the scene.

Witnesses said that a neighbor waded onto the flat-water bridge and carried the children to safety and that Lisa Hilton managed to swim to shore after being swept under by the surging stream.

“She was extremely lucky,” said her husband, Steve Hilton, a grandson of the late hotel scion Conrad Hilton.

The creek, which feeds into the Pacific Ocean at the mouth of Bonsall Canyon, flooded several expensive houses. The floodwaters left at least two houses on Bonsall Drive marooned, including that of rock singer Pat Benatar.

The storm buffeted the eastern half of Ventura County with more than four inches in eight hours, flooding streets and homes, causing dozens of accidents and causing the county’s flood control channel to breach its banks.

By midafternoon, Moorpark had received 5.09 inches of rain in the 36 hours since 8 a.m. Sunday morning.

“I don’t think we’ve ever seen that before in Ventura County,” said Dolores Taylor, county hydrologist.

The storm caused dozens of minor injury accidents, closed numerous county and city streets and sent mudslides oozing onto area highways, closing California 33 above the tiny resort community of Ojai.

The National Weather Service issued an urban and small-stream flood advisory, urging motorists to use caution and not try to cross flooded streets.

In Orange County, officials reported only minor problems, citing last week’s storm as the reason.

“Maybe people learned how to drive in the rain,” mused CHP Officer Angel Johnson. “They’ve had some practice recently, I guess.”

Times staff writers Leslie Berger, Richard Lee Colvin, Ashley Dunn and Tracey Kaplan reported from Los Angeles; Ron Russell from Malibu; Joanna M. Miller from Ventura County; David Reyes from Orange County and Lisa Omphroy from San Diego.