Assault barrels head to California; Evacuation warnings issued in SoCal

Evacuation warnings were issued for burn scars across Los Angeles County — including Palisades, Altadena, Sylmar and Hollywood Hills — as a winter storm began sweeping through the state Monday, bringing the first big dump of snow of the season to the Sierra.

The storm, which is expected to bring rain to Southern California by nightfall, was already hitting Northern California Monday afternoon, causing hundreds of flight delays at the San Francisco airport and flood advisories in San Francisco, Oakland and Napa. Web cameras at Mammoth Mountain Resort and Bear Valley Resort showed the storm rolling in and covering the slopes in white.

At 3:30 p.m., the National Weather Service announced that the risk of large and damaging debris flows in burn scars in the Los Angeles area had increased and urged residents to pay attention to guidance from law enforcement. The storm is expected to bring four to six hours of rain, powerful wind gusts and potential thunderstorm and tornado activity, according to the weather service.

Here’s what forecasters are predicting, although they warn that the situation is evolving and is subject to change.

Monday to Tuesday

Isolated showers began hitting the Bay Area Monday morning, with precipitation intensifying around noon and accumulating a half-inch to an inch around 4:30 p.m., according to weather service meteorologist David Gomberg.

The core of the storm, which is expected to have the most devastating impacts, is expected to reach San Luis Obispo and Santa Barbara counties Monday evening, as well as Los Angeles County between midnight and 2 a.m., Gomberg said. These areas may experience light showers before and after the passage of the core.

“We could see strong, even locally severe thunderstorms, which means you can have wind gusts up to 60 miles per hour. … They can take down trees and power lines,” Gomberg said. “There is even the possibility of a few isolated downpours and tornado activity across the county.”

Evacuation warnings are in place near burn scars from the Palisades and Eaton fires, as well as the Hurst fire in Sylmar and the Sunset fire in the Hollywood Hills.

“Residents in these areas are urged to remain vigilant, monitor official weather updates and avoid unnecessary travel during the storm, especially if they have been informed of potential mudslide hazards in their neighborhood,” the Los Angeles County Sheriff’s Department said.

Los Angeles Mayor Karen Bass urged residents to sign up for emergency alerts at NotifyLA.org and said the city was preparing for possible flooding and mudslides.

“The city has reinforced hillsides and vulnerable areas against possible debris flows in recent burn areas – these resources remain in place,” Bass said in a statement. “Today, we deployed resources strategically to the Palisades and throughout the city, including response teams, rescue teams and helicopters.”

Peak rain rates of 0.25 to 0.5 inches of rain per hour are possible, with total accumulations of 0.75 to 1.5 inches for coastal areas and valleys and 1.5 to 3 inches in the mountains, according to the weather service.

As of 8 p.m. Monday, a flood watch is in effect for areas in and near recent burn scars in southern and central California. The scars come from the Gifford, Madre, Lake, Apache, Mountain, Post, King, Canyon, Hughes, Hurst, Kenneth, Franklin, Palisades, Sunset, Lidia, Hawk, Eaton and Bridge fires that burned over the past two years. A flood watch is in effect until 3 p.m. Tuesday. Debris flows are also possible.

Flooding could also occur in urban areas, poorly drained areas and crossings with low water levels, forecasters said.

The National Weather Service also issued a flood alert for burn scars in the San Bernardino County Mountains, Santa Ana Mountains, foothills and inland areas of Orange County from Monday evening through Tuesday afternoon. The burn scars include those caused by the Bridge, Line, Apple, El Dorado and Airport fires that burned over the past five years.

Forecasters predict precipitation rates of 0.3 to 0.7 inches per hour in these areas.

For much of the high desert, including Apple Valley and Lucerne Valley, San Gorgonio Pass near Banning, Antelope Valley and the Morongo Basin, a wind advisory is in effect until 11 p.m. Tuesday, with gusts of up to 45 mph expected.

Farther north, along the Central Coast and in the Central Sierra, the strongest part of the storm is expected to hit between 11 p.m. Monday and 5 a.m. Tuesday, said Emily Wilson, a meteorologist with the National Weather Service in Hanford.

Snow levels are expected to drop to 6,000 feet, with accumulations of 4 to 8 inches from 7,000 to 8,000 feet and 1 to 2 feet above 9,000 feet. At lower elevations, hourly rain rates could range from 0.2 to 0.3 inches per hour, she said.

A Flood Watch is in effect from Monday at 5 p.m. through Tuesday afternoon for rural and mountainous areas including Camp Nelson, Coarsegold, Oakhurst, Kernville, Fish Camp, Lake Isabella, North Fork, Auberry, Bass Lake and Yosemite Valley. A winter storm warning is in effect until 5 p.m. Wednesday for some communities near Yosemite National Park and Sequoia and Kings Canyon national parks, as well as on the eastern slopes of the Sierra.

Tuesday to Wednesday

Showers may persist, but by Tuesday afternoon the most damaging impacts of the storms should be over.

Cooler temperatures are expected to persist across the state through Thursday, followed by a warming trend.

The first frost of fall is expected in the Owens Valley, with overnight lows between 27 and 32 degrees. A Freeze Watch is in effect until Wednesday morning for Bishop, Independence, Lone Pine and Olancha.