Storm: High Surf Expected At Palos Verdes, Los Angeles Beaches

RANCHO PALOS VERDES, CA — The National Weather Service has issued a high surf advisory as a wet and potentially damaging storm is expected to hit the Southland Thursday, bringing what forecasters call an "atmospheric river" of moisture that will persist into Friday.

The agency issued the high surf advisory through 10 a.m. Friday. Beachgoers are urged to use caution and be mindful of dangerous rip currents and sneaker waves.

"Swim near a lifeguard," the National Weather Service reported. "If caught in a rip current, relax and float. Don't swim against the current. If able, swim in a direction following the shoreline. If unable to escape, face the shore and call or wave for help."

Rain was falling Wednesday over San Luis Obispo County, where the system remained largely stalled.

"The front sags southward into Ventura and Los Angeles counties by Thursday afternoon into Friday," according to the National Weather Service. "Heaviest rainfall across the southern counties will occur Thursday night into Friday morning. Several inches of rain are expected with flooding concerns including recent burn areas. Several feet of high elevation mountain snow is also expected, along with moderate to strong winds."

The National Weather Service initially issued a winter storm watch for the Los Angeles County mountains, excluding the Santa Monica range, from Thursday afternoon through Friday afternoon, but the agency later upgraded it to a winter storm warning. The 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."

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."

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.

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.

Here's the forecast for the Palos Verdes Peninsula:

Thursday: Rain, mainly after 4 p.m. High near 60. Breezy, with a southeast wind 15 to 20 mph, with gusts as high as 25 mph. Chance of precipitation is 80%.

Thursday night: Rain and possibly a thunderstorm before 10 p.m., then showers and possibly a thunderstorm after 10 p.m. Low around 49. Breezy, with a south wind 15 to 20 mph, with gusts as high as 25 mph. Chance of precipitation is 100%.

Friday: Showers and possibly a thunderstorm. High near 57. West wind around 15 mph. Chance of precipitation is 90%.

Friday night: Partly cloudy, with a low around 46. West wind around 10 mph, with gusts as high as 15 mph.

Saturday: Sunny, with a high near 58. Northeast wind around 5 mph becoming southwest in the afternoon.

Saturday night: Mostly clear, with a low around 47.

Sunday: Partly sunny, with a high near 64.

Sunday night: Mostly cloudy, with a low around 51.

Monday: Cloudy, with a high near 62.

Monday night: Mostly cloudy, with a low around 50.

Tuesday: A slight chance of rain. Partly sunny, with a high near 60.

Tuesday night: A slight chance of rain. Partly cloudy, with a low around 48.

Wednesday: Sunny, with a high near 60. Breezy.

- City News Service and Patch Editor Nicole Charky contributed to this report.