Powerful holiday storm lashes Southern California and threatens mudslides in fire-scarred areas

A powerful winter storm swept across Southern California on Wednesday, with heavy rain threatening mudslides in areas scorched by wildfires, bringing near white-out snow conditions in the mountains and hazardous travel for millions of holiday drivers.

Forecasters said Southern California could see its wettest Christmas in years and warned about flash flooding, which could soon hit parts of Santa Barbara and Ventura counties, the National Weather Service said. Other parts of Southern California were under wind and flood advisories. Further north, much of the Sacramento Valley and the San Francisco Bay Area were under a flood watch and high wind warning through Friday.

Conditions could worsen as multiple atmospheric rivers moved across the state during one of the busiest travel weeks of the year.

“If you’re planning to be on the roads for the Christmas holidays, please reconsider your plans,” said Ariel Cohen, a National Weather Service meteorologist in Los Angeles.

Forecasters warned that heavy snow and gusts were expected to create “near white-out conditions” Wednesday in parts of the Sierra Nevada and make it “nearly impossible” to travel through the mountain passes.

Southern California typically gets half an inch to 1 inch (1.3 to 2.5 centimeters) of rain this time of year, but this week many areas could see between 4 and 8 inches (10 to 20 centimeters), National Weather Service meteorologist Mike Wofford said. It could be even more in the mountains. Gusts could reach 60 to 80 mph (97 to 128 kph) in parts of the central coast.

Atmospheric rivers transport moisture from the tropics to northern latitudes in long, narrow bands of water vapor that form over an ocean and flow through the sky.

In areas scorched by January’s wildfires, Los Angeles County officials said they were going door to door at about 380 especially vulnerable homes, ordering residents to evacuate because of the risk of landslides and debris flows.

“The threat posed by this storm is real and imminent,” Los Angeles Police Department Chief Jim McDonnell said. He urged people in burn scar areas to reconsider trying to ride out the storm at home. Parts of Los Angeles were under evacuation warnings.

Officials have taken steps to reduce the risk in and around the burn scars, with Los Angeles County installing K-rails, a type of barrier to help catch sliding debris from burned areas, as well as offering free sandbags to residents.

Road closures, downed trees, power outages and flight delays are expected as the storm continues through the week, officials said.

The storm has already caused damage in Northern California, where flash flooding led to water rescues and at least one death, authorities said. Shasta County Sheriff Michael L. Johnson declared a local state of emergency earlier this week to prepare for more rain and allow for additional search-and-rescue and hazard-mitigation efforts.

Forecasters warned of severe thunderstorms and even a small chance of tornadoes along the northern coast.

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