Governor has 21 counties under emergency orders while 16m people in the state are under flood watch warnings

An impending atmospheric river and rapidly melting snow has put communities across California on high alert for flash flooding, mudslides and rockslides as the subtropical storm surge moves over the state. Rivers and streams could also quickly rise beyond capacity and breach, the National Weather Service warned. Overall, some 16 million people are under flood watch warnings.

The state’s governor, Gavin Newsom, has declared a state of emergency for 21 counties, including some mountain communities still digging themselves out from the snow. “The state is working around the clock with local partners to deploy life-saving equipment and first responders to communities across California,” Newsom said on Wednesday evening. “With more dangerous storms on the horizon, we’ll continue to mobilise every available resource to protect Californians.”