Southern California’s strongest storm of the winter is here: ‘High risk of flooding, debris flow’
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• The peak of the storm is forecast for Thursday.
• Flood watch for burn scars in L.A. and Ventura counties starts Thursday afternoon.
The first wave of the strongest storm of the winter began hitting Southern California on Wednesday, but the most damaging rains are expected Thursday.
“The event has started,” the National Weather Service said in a Wednesday morning forecast update. “As forecast a blob of moisture has raced out in front of the main storm, which is still on track to arrive Thursday.”
Los Angeles County officials said they are focusing their resources on the area’s burn scars, which are just weeks removed from one of the most destructive fire seasons in California history. The National Weather Service warned of the “high risk of flooding, debris flow [and] damaging winds.”
Storms will be hitting virtually all parts of California this week, from the Bay Area to San Diego County.
“Time for a little wet weather,” the National Weather Service’s San Diego office shared on X. “Showers will move through much of the area for your Wednesday.”
A worst-case scenario for L.A. County in this storm could involve heavy rainfall over recently burned areas that dissolves soil into flows of debris barreling down hillsides at speeds of up to 35 mph, covering cars and homes with thick muck and putting them at risk of being struck by boulders.
“Thursday is the time of most concern, when the winds and the rain will be the strongest,” said Ryan Kittell, a meteorologist with the weather service’s office in Oxnard. Most areas of Southern California should see light rain sometime on Wednesday, and there’s likely to be a break before more widespread rain starts to develop again starting later that night or Thursday morning.
The highest risk for debris flows and road flooding in Los Angeles and Ventura counties is between midday Thursday and 6 a.m. Friday. For Santa Barbara and San Luis Obispo counties, the peak risk is from 6 a.m. Thursday through midnight Friday.
After blistering criticism that Southern California officials weren’t prepared ahead of the historic firestorms, government authorities say they have worked to reduce the risk of flooding impacts. Crews have rushed to clear out basins designed to catch mud, rocks and other debris from tumbling into neighborhoods and installed thousands of sandbags and compost filter socks — a type of berm — to keep debris from flowing into storm drains.
In Southern California this week, Kittell said the most likely outcome was “shallow” debris flows in burn scars, covering roads with mud. Thicker mudflows might be capable of immersing parked cars in mud.
“There’s also a risk for more significant debris flows, where it starts to impact a few vulnerable structures,” Kittell said. “While that isn’t the most likely outcome, the risk is there,” spurring widespread flood watches.
Flood watches, in effect for all recent burn areas in Los Angeles and Ventura counties, are set to take effect starting Thursday at 1 p.m. and lasting through 4 a.m. Friday. A flood watch for Santa Barbara County’s Lake fire burn scar will be in effect from Thursday at 10 a.m. through Friday at midnight.
And all of San Luis Obispo County will be under a flood watch from Thursday at 4 a.m. through Friday at noon.
A flood watch is also expected for a wide swath of San Diego and Orange counties and the Inland Empire beginning Thursday morning and lasting through late Thursday night.
The highest risk of excessive rainfall — the type that could produce flash flooding — will be in downtown L.A., South L.A., the Westside, the San Gabriel and San Fernando valleys, and large swaths of Ventura and Santa Barbara counties.
The threat from this storm extends across California.
By Thursday morning, soils around the San Francisco Bay Area may be sufficiently saturated that there may be “widespread shallow landslides” in the wettest areas, the weather service office in Monterey said, adding that strong winds could lead to damaged trees and power outages.
Meteorologists were closely watching for potential flooding of Sonoma County’s Russian River near Guerneville and Mark West Creek, and the San Lorenzo River, which travels through the heart of Santa Cruz County.
Flood watches are expected in San Francisco, San Mateo, Santa Cruz, Monterey, Sonoma and Marin counties from 10 p.m. Wednesday to 10 p.m. Saturday. From Wednesday night through Friday, a flood watch is also expected for the Sierra foothills east of the San Joaquin Valley.
Heavy snow was expected in the Sierra Nevada, with 2 to 4 feet expected along the Sierra crest near Lake Tahoe, and 10 to 18 inches at lake level. In Mono County, home to Mammoth Mountain, 4 to 5 feet of snow could fall along the Sierra crest.
In Southern California, burn areas most at risk are those scorched in the Palisades and Franklin fires in Pacific Palisades and Malibu; the Eaton fire in the Altadena area; and the Bridge fire in the San Gabriel Mountains, west and southwest of Wrightwood.
“They’re in areas which tend to get enhanced rainfall amounts and rates,” Kittell said. But all fresh burn scars have some risk of debris flows.
Over the three-day storm, the Palisades scar is expected to receive 3.35 inches of rain; the Eaton scar, 4.53 inches; and the Bridge scar, 4.95 inches. Downtown Los Angeles could get 2.09 inches of rain; Long Beach, 2.22 inches; Santa Barbara, 3.02 inches; San Luis Obispo, 3.82 inches; and Cambria, 4.88 inches.
The last time downtown L.A. received that much rain was the 2024 Easter weekend storm, from March 29 to 31, when 2.1 inches fell. The difference with that storm, however, is that it came following two consecutive wet winters, and did not follow severe wildfires.
By Friday, Palm Springs could get seven-tenths of an inch of rain; San Diego, up to 1.5 inches; Riverside, Irvine, Oceanside, Escondido and San Clemente, up to 2 inches; San Bernardino and Riverside, up to 2.5 inches.
For San Diego and Orange counties and the Inland Empire, the storm is expected to be neither a washout nor “the worst storm we’ve ever seen,” said Alex Tardy, meteorologist with the National Weather Service office in San Diego.
Although “not catastrophic,” he said, “we are going to see some locally heavy rainfall, and that could cause some flooding, especially mud and debris on our burn scars, and then your normal urban flooding.”
As forecasters watch the burn scars, they’ll be paying particular attention to rainfall rates. The risk for debris flow in recently burned areas start at around half an inch per hour.
“With our burn scars, intensity trumps total accumulations,” Kittell said. “So it’s not how much rain falls over a long period of time, but how much rain falls in a short period of time.”
Los Angeles, Ventura, Santa Barbara and San Luis Obispo counties could see intense rainfall rates of between half an inch to 1 inch per hour during the peak of the storm.
“Enhanced cells,” he said, could bring short bursts of precipitation — “30 to 60 minutes of pretty intense rainfall.”
The risk of thunderstorms has increased and is now estimated to be 10% to 20% on Thursday, up from 5% to 10%, Kittell said.
Significant wind gusts from the south are expected. Covina could see a peak wind gust of 21 mph; downtown L.A., 23 mph; Long Beach, 26 mph; Redondo Beach and Santa Barbara, 30 mph; Canoga Park and Santa Clarita, 32 mph; Thousand Oaks, 35 mph; Pyramid Lake, 37 mph; San Luis Obispo, 44 mph; Santa Maria, 45 mph; Lancaster, 52 mph; and Acton, 53 mph.
“These are some pretty high numbers, especially if you look at the Central Coast,” Kittell said. Areas of the Central Coast, including around Cambria, are at high risk of downed trees.
Officials urged residents to sign up for emergency alerts with their local agencies. In Los Angeles County, residents can sign up at Ready.LACounty.gov.
They also advised people to stay off the roads if possible on Thursday and heed evacuation warnings if they are issued. On Tuesday, Santa Barbara County issued an evacuation warning for the area in and around the burn zone of the Lake fire in the mountains north of Los Olivos. That fire scorched more than 38,000 acres in the Los Padres National Forest in 2024.
After this storm exits, no more rain is expected next week, and possibly for the rest of February, Kittell said. Forecasters expect warmer weather starting by this weekend.
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