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Storm weakens but rains are on their way as mountain areas prepare for slides

October 13, 2009 |  3:12 pm

Weakened after dousing Northern California with heavy rains this morning, the first storm of the season is expected to move into Southern California this evening, bringing high winds and at least a half-inch of rain to the Los Angeles area and keeping mountain communities on guard against potential floods and mudslides.

"It's raining itself out," said Jamie Stern, a spokeswoman for the National Weather Service's Oxnard office.

Southern Californians in valleys and coastal areas should expect less than an inch of rain, she said, but a stronger downpour of up to 4 inches is possible in the mountains. "At this point we still have the rain moving down toward us, although it has weakened," she said.

A flash-flood watch issued for the burn areas from Santa Barbara to San Bernardino counties will remain in effect through Wednesday, the weather service said.

Slick roads and the threat of mudslides have prompted the closure of several mountain roads in the area burned by the massive Station fire.

Officials said residents in burn areas should prepare for possible mudslides, rock slides and debris flows "even during periods with little or no rain falling."

"Across Los Angeles County, the threat of heavy rain is greatest late tonight and Wednesday morning," according to a weather service statement. "Flash flooding and debris flows will be a particular threat in and below the recent burn areas."

The powerful winter storm battered Northern California today, causing power outages and flooding in the Bay Area, and prompting officials in the Santa Cruz area to order evacuations of homes in the mountains, where summer wildfires have made terrain prone to mudslides.

The unusual fall storm is the product of a collision of a storm from Alaska with the subtropical moisture of the remnants of a typhoon from the western Pacific.

Flood watches extend to land charred by the Sheep fire near Wrightwood as well as areas burned by the Sayre and Marek fires last year in the San Fernando Valley area.

A high-wind warning is in effect for all L.A. County mountain areas, excluding the Santa Monica Mountains, until Wednesday morning, with winds of 35-40 mph, with gusts up to 60 mph, predicted.

The storm system is wetter than normal for October, when the average rainfall for the entire month is about half an inch, weather officials said. The rains are being driven by strong winds blowing from the south, intensifying rainfall on south-facing mountain slopes that burned from Altadena to Acton during the 250-square-mile Station fire that broke out in August.

The U.S. Geological Survey released a grim forecast last week for communities hit by the Station fire, saying major mudslides are likely during the winter rainy season. The locations most at risk for mudslides are La Cañada Flintridge, La Crescenta and a few areas of Pasadena against the San Gabriel Mountains, geologists said.

The California Highway Patrol has closed some mountain roads because of the coming rains, said Officer Francisco Villalobos, a spokesman for the agency. Big Tujunga Canyon Road is closed 1 1/2 miles north of Mount Gleason Avenue to Angeles Forest Highway. Aliso Canyon Road was closed in the Angeles National Forest.

Authorities reported an increase in the number of accidents this morning, with about 140 collisions on Los Angeles County highways between 6 and 9 a.m. compared with 60 during that period last week.

Weather and traffic officials advised drivers to watch out for slippery conditions during the evening commute.

"It's the first significant rainfall of the season," said Rich Thompson, a weather service meteorologist. "So the roads can be slicker than you might expect because of all the oil coming up."

-- Tony Barboza