LOS ANGELES (CNS) - After dropping "epic" amounts of rain in San Luis Obsipo County, a storm front was moving slowly toward the Southland today, and forecasters warned of potentially damaging mud and debris flows from what could be an intense night of downpours.
Forecasters said the "atmospheric river event" had already dropped nearly 14 inches of rain in some parts of San Luis Obispo County over the past 36 hours. The storm was driving slowly south, with rain expected to fall in Ventura County by early evening, reaching Los Angeles County around roughly 6 p.m.
"As the storm shifts south later today and tonight, heavy rain is expected to spread into the recent burn scars in Los Angeles County, including the Lake, Bobcat and Ranch 2 burn scars," according to the National Weather Service.
A winter storm warning will be in effect from 3 p.m. Thursday to 3 p.m. Friday, with 1 to 3 feet of snow potentially accumulating at elevations above 6,000 feet.
A flash flood watch will be in effect Thursday afternoon through late Thursday night for the mountains and the Antelope, Santa Clarita and San Gabriel valleys, mainly affecting areas near the Lake, Bobcat and Ranch 2 burn areas. Forecasters said the areas could see rain rates of 0.75 inches per hour, potentially leading to "significant mud and debris flows."
"Residents in or below the recently burned areas are urged to take the steps necessary to protect their property," according to the NWS. "Persons in the watch area should remain alert and follow directions of emergency-preparedness officials. Avoid hiking and camping in canyons and near creeks."
A flood watch will be in effect for most of Orange County from Thursday afternoon through Friday afternoon. Forecasters said the heaviest rain there is anticipated to begin before midnight Thursday night, continuing through Friday morning, including a chance of thunderstorms and rain rates topping a half-inch per hour.
The Orange County Sheriff's Department on Thursday morning issued voluntary evacuation warnings for residents in Silverado, Williams and Modjeska canyons, noting the potential for "heavy rain, subsequent flooding and debris flows" in the recent Bond Fire burn area.
Santiago Canyon road was opened only to residents east of the 241/261 interchange, and north of Ridgeline Road.
The Red Cross was expected to open a "temporary evacuation point" at 2 p.m. at El Modena High School, 3920 E. Spring St. in Orange, to offer resources to evacuees, such as snacks and information on available hotels and lodging. The evacuation point will not be operated as a shelter.
Winds in mountain areas will blow at 20 to 30 mph, with gusts ranging up to 50 mph. A wind advisory will be in effect for Los Angeles County mountains until 3 p.m. Thursday. Forecasters said the strongest winds are likely in the San Gabriel Peaks and the Grapevine area, making "driving difficult, especially for high-profile vehicles."
According to the NWS, the low-pressure system was gathering strength off the Oregon coast, and will likely remain mostly stationary through Thursday.
"This will create a steady and nearly persistent stream of moist southwest flow, known as an atmospheric river, focused over San Luis Obispo and Santa Barbara counties ... lasting through at least Thursday with two to three days of nearly constant rain," according to the weather service.
Forecasters said Los Angeles County could see 1.5 to 3.5 inches of rain, with 2 to 5 inches possible in the foothills and mountains, although the largest rainfall totals are likely to occur in Ventura County.
Whenever persistent rain is in the forecast, fears are raised about possible mudslides.
"With the potential of this event, the area may approach critical thresholds for mud and debris flows in and around the recent burn areas," according to the NWS.
Los Angeles County health officials have issued a cold weather alert through Thursday for the mountains and Antelope Valley, and through Tuesday for the Santa Monica Mountains and the Santa Clarita Valley.