Atmospheric river to bring more snow, rain and floods to California

California is facing yet another dangerous winter storm, expected to bring heavy precipitation that could lead to flash flooding this weekend.

The extreme weather is the latest in a series of storms that have battered the state this month, leading California's governor to declare an emergency.

The National Weather Service has warned of a high risk of excessive rainfall on Friday through Saturday.

"Lives and property are in great danger," it said.

"Areas that normally do not experience flash flooding will flood," the weather service added.

Nearly all of California's 39 million residents were under some type of weather warning as of Friday morning.

The "burst of heavy precipitation", according to the weather service, is caused by a powerful atmospheric river, which began on Thursday.

Atmospheric rivers occur when water evaporates into the air and is carried along by the wind, forming long currents that flow in the sky like rivers flow on land. They can lead to severe rain and mountain snow.

The heaviest precipitation is expected to hit central California, while "copious amounts of heavy snow" could make travel dangerous in parts of northern California and the Sierra Nevada mountain range, where mudslides and rockslides are also possible, according to the weather service.

As much as 10 inches of rain in 24 hours could fall in some parts of the state where there is snowpack, meaning the "potential for widespread flooding is considerable", the Weather Service said.

Flash flooding causes several deaths each year, according to the National Weather Service, which urged California residents to steer clear of barricaded and flooded roads.

The atmospheric river comes as California is still reeling from a series of extreme weather events in February and March. Last week, California Governor Gavin Newsom declared a state of emergency in more than a dozen counties in the state amid one of California's wettest winters on record.

Mr Newsom expanded the emergency on Thursday to include 21 more counties.

At least eight deaths are being investigated as possibly related to the weather, while one death has been conclusively tied to the storms.

"With more dangerous storms on the horizon, we'll continue to mobilize every available resource to protect Californians," Mr Newsom said.

Residents near Big Sur in California were told this week to stock up on enough supplies to last them at least two weeks ahead of the latest storm.

The weather is also expected to blanket parts of Nevada, Oregon and Idaho with as much as 6 to 12 inches of snow on Friday.