Heavy rain storms across large parts of California triggered floods and mudslides, leaving three people dead as of Christmas night, according to local officials.

The storms, expected to persist through Friday, have inundated parts of Los Angeles County with up to 11 inches (27 cms) of rain, necessitating evacuations and causing major road closures.

Emergency responders have conducted several rescues, including saving individuals trapped in vehicles as rising floodwaters swept through neighborhoods. In response, California's Governor Gavin Newsom declared a state of emergency on Wednesday for Los Angeles and other southern California counties.

Power outages affected about 100,000 residents throughout the state as of Thursday evening.

The US Weather Prediction Center warned of the potential for numerous flash flooding events, cautioning that many rivers and streams could overflow their banks.

Fatalities include a 64-year-old man from San Diego, killed by a fallen tree, and a 74-year-old who drowned in Redding while police attempted to rescue him.

A woman in her 70s also died Monday after being swept into the ocean by a large wave at MacKerricher State Park in Mendocino County.

Evacuation warnings were issued for some San Bernardino County residents, and flash flood alerts extended into the San Francisco Bay Area on Thursday.

In the Bay Area, wind gusts reached over 100 mph (161 km/h) at a monitoring station near San Jose.

Additionally, in Altadena, rainfall caused mudslides in areas previously scorched by wildfires, impacting the land's capacity to absorb water.

Los Angeles Mayor Karen Bass declared a local emergency, urging residents to exercise caution while traveling amidst the holiday rush. I am urging all Angelenos to stay safe and be extremely careful on the roads if you absolutely must travel, Bass stated, highlighting the serious nature of the storm.

The storms developed from multiple atmospheric rivers that have brought extensive moisture from the tropical regions, coinciding with one of the busiest travel weeks of the year.