Los Angeles: A powerful winter storm swept across California on Wednesday, with heavy rains and gusty winds bringing mudslides and debris flows that have led to some water rescues and evacuation orders.

Forecasters said Southern California could see its wettest Christmas in years and warned about flash flooding and mudslides. Areas scorched by January's wildfires were under evacuation warnings, and Los Angeles County officials said the previous day that they delivered about 380 evacuation orders to especially vulnerable homes.

San Bernardino County firefighters said they rescued people trapped in their cars when mud and debris rushed down a road leading into Wrightwood, a mountain resort town in the San Gabriel Mountains about 80 miles (130 kilometres) northeast of Los Angeles. It was not immediately clear how many were rescued.

Firefighters also went door to door to check on residents, and the area was under a shelter-in-place order, officials said. Lytle Creek, also in the San Gabriel Mountains, was under evacuation orders in the afternoon as rains continued to pummel the area.

Debris and mud were seen cascading down a road in Wrightwood in a video posted by county fire officials. Another video showed fast-moving water rushing through the front porch of several homes.

The storm stranded Dillan Brown with his wife and 14-month-old daughter at a rented cabin in Wrightwood with almost no food and only enough diapers for about another day. By the morning, roads leading off the mountain and to a grocery store were blocked by rocks and debris, Brown said.

“I came across (a road) where there was a car sucked away by the water and realised we were trapped here,” he said.

A resident learned of his situation and posted a call for help in a Facebook group, and in less than an hour, neighbours showed up with more than enough supplies to ride out the storm, including bread, vegetables, milk, diapers and wipes.

“I think we're a little sad and upset that we're not going to be home with our families,” Brown said, but the “kindness shown is definitely an overwhelming feeling.”

Janice Quick, president of the Wrightwood Chamber of Commerce and a resident of the mountain town for 45 years, said a wildfire in 2024 left much of the terrain without tree coverage and “all this rain is bringing down a lot of debris and a lot of mud from the mountain area.”

Residents around the burn scar zones from the Airport Fire in Orange County were also ordered to evacuate.

Areas along the coast, including Malibu, were under flood warnings until the evening, and much of the Sacramento Valley and the San Francisco Bay Area were also under wind and flood advisories.

Heavy rain douses Southern California

Several roadways, including a part of Interstate 5 near the Burbank Airport, were closed due to flooding.

Conditions could worsen with multiple atmospheric rivers during one of the busiest travel weeks of the year.

The rain began tapering off in the evening in Los Angeles, but another storm system was on the horizon with showers and possible thunderstorms on Christmas Day.

James Dangerfield, an 84-year-old resident of Altadena, said his family and neighbours helped place sandbags in his backyard earlier this week. A flash flood warning was issued for the neighbourhood, but he wasn't too worried because his house is on a hill.

He and his wife, Stephanie, planned to remain there and spend Christmas Eve with their two adult daughters and grandchildren.

“We're just going to stay put, and everybody will have to come to us,” Dangerfield said. “We're not going to go anywhere.”

Mike Burdick, who takes care of his parents in Altadena near burn scars from the Eaton Fire, ran out to buy more sandbags in the morning when he saw that the pool was overflowing.

“I literally woke up to just downpour,” he said.

The family was prepared to evacuate with a week's worth of essentials, including for their dog and cat.

Southern California typically gets half an inch to 1 inch (1.3 to 2.5 centimetres) of rain this time of year, but this week, many areas could see between 4 and 8 inches (10 to 20 centimetres) with even more in the mountains, National Weather Service meteorologist Mike Wofford said.

Much of California under weather warnings

Forecasters said heavy snow and gusts were expected to create “near white-out conditions” in parts of the Sierra Nevada and make travel “nearly impossible” through mountain passes. There was also a “considerable” avalanche risk around Lake Tahoe, according to the Sierra Avalanche Center.

The National Weather Service said a winter storm warning would be in effect for the greater Tahoe region until Friday morning.

Power was knocked out to more than 125,000 due to a damaged power pole, according to the Pacific Gas and Electric Co utility.

The California Highway Patrol was investigating a seemingly weather-related crash south of Sacramento in which Sacramento Sheriff Deputy James Caravallo died. Caravallo was apparently travelling at an unsafe speed, lost control on a wet road and crashed into a power pole, CHP Officer Michael Harper said via email.

Caravallo was with the sheriff's office for 19 years, the agency said in a post on social media.

“Our hearts are with Deputy Caravallo's family, and we ask the public to keep Deputy Caravallo's loved ones and our Sheriff's Office family in their thoughts and prayers,” it said.

A flash flood warning was issued for portions of Sacramento in the evening as more severe weather developed offshore and began moving inland.

Gov. Gavin Newsom declared a state of emergency in six counties to allow state assistance in storm response.

The state deployed emergency resources and first responders to several coastal and Southern California counties, and the California National Guard was on standby.

Atmospheric rivers transport moisture from the tropics to northern latitudes in long, narrow bands of water vapour that form over an ocean.