A massive storm unleashed high winds and torrential rains across California on Thursday, threatening much of the state with flash flooding and mudslides, leaving a child dead and knocking out power to tens of thousands.

The “atmospheric river”– an airborne current of dense moisture flowing from the ocean – was expected to persist, drenching much of California with heavy rains at a rate of 1 inch (2.5 cm) per hour, the National Weather Service (NWS) said, with dangerous, gale-force gusts forecast throughout the day.

Overnight, a child younger than 2 years old was killed when a tree fell on his home in Occidental, a community of about 1,100 people 65 miles (105 km) north of San Francisco, local media reported. Authorities did not provide more specific information.

Some 180,000 homes and businesses were without power early on Thursday, according to data by Poweroutage.us, after high winds downed power lines and trees across the state overnight.

Atmospheric rivers will become larger — and possibly more destructive — because of warmer air and water temperatures from climate change, scientists say.

Governor Gavin Newsom declared a state of emergency on Wednesday, and state officials urged Californians to avoid travel during the storm.

Crews in San Francisco spent the night cleaning up debris from felled trees that blocked roadways. The city’s fire department rescued a family trapped when a tree fell across their car.

Sonoma County residents living near the Russian River between Healdsburg and Jenner were advised by authorities to evacuate their homes, with the waterway forecast to crest at 33 feet (10 meters) late Thursday before receding below flood stage. The area lies in the heart of the Sonoma Wine Country, a tourist magnet just north of San Francisco.

Evacuation warnings were also in place in coastal communities such as Santa Cruz. Officials shut down a 55-mile stretch of Route 1, a scenic highway that runs along the coast, due to flooding and debris.

Authorities warned the heavy downpours would likely unleash flash floods and mudslides, especially in areas where the ground remained saturated from a previous deluge that soaked northern California days earlier.

Fire-ravaged hill slopes stripped of vegetation were also particularly vulnerable to slides. In Santa Barbara County, homes in three areas where wildfires left burn scars behind were ordered to evacuate.

Nearly 100 flights were canceled at San Francisco International Airport on Wednesday, and an additional 15 had already been canceled on Thursday.

The storm was also bringing extremely heavy snow to the Sierra Nevada Mountains – more than 3 inches (7.6 cm) per hour over 5,000 feet (1,500 meters), the NWS said – making travel in those areas dangerous or impossible.

The rain was beginning to taper on Thursday morning, said Bob Oravec, a NWS meteorologist, though it was still inundating much of the state.

But forecasters predict more storms will move through the state in the coming days, with 10 additional inches of rain likely in the next week across northern and central California, Oravec said.

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