A strong storm system that has brought relentless winds, rain and snowfall to California was expected to ease on Friday, but there was still a risk of high surf along the coast, flash flooding near Los Angeles and avalanches in the Sierra Nevada.

Waves near the San Francisco Bay Area could reach up to 25ft (7.6 meters) on Friday, parts of southern California were at risk of flooding, and avalanches could hit the Lake Tahoe area, officials warned. Residents were told to be ready to evacuate the mountain town of Wrightwood about 80 miles (130km) north-east of Los Angeles because of mudslides.

Atmospheric rivers carried massive plumes of moisture from the tropics during one of the busiest travel weeks of the year. The storms were blamed for at least two deaths earlier in the week.

The system brought the wettest Christmas season to downtown Los Angeles in 54 years, the National Weather Service said.

Roads in the 5,000-resident town of Wrightwood were covered in rocks, debris and thick mud on Thursday. With power out, a gas station and coffee shop running on generators were serving as hubs for residents and visitors.

“It’s really a crazy Christmas,” said Jill Jenkins, who was spending the holiday with her 13-year-old grandson, Hunter Lopiccolo.

Lopiccolo said the family almost evacuated the previous day, when water washed away a chunk of their backyard, but they decided to stay and still celebrated the holiday. Lopiccolo got a new snowboard and e-bike.

“We just played card games all night with candles and flashlights,” he said.

Davey Schneider hiked a mile and a half (1.6km) through rain and flood water up to his shins from his Wrightwood residence on Wednesday to rescue cats from his grandfather’s house.

“I wanted to help them out because I wasn’t confident that they were going to live,” Schneider said on Thursday. “Fortunately, they all lived. They’re all OK – just a little bit scared.”

Arlene Corte said roads in town turned into rivers, but her house was not damaged.

“It could be a whole lot worse,” she said. “We’re here talking.”

With more rain on the way, more than 150 firefighters were stationed in the area, said Shawn Millerick, San Bernardino county fire department spokesperson.

“We’re ready,” he said. “It’s all hands on deck at this point.”

A falling tree killed a San Diego man on Wednesday, news outlets reported. Farther north, a Sacramento sheriff’s deputy died in what appeared to be a weather-related crash.

Areas along the coast, including Malibu, were under a flood watch until Friday afternoon, and wind and flood advisories were issued for much of the Sacramento valley and the San Francisco Bay Area.

Southern California typically gets half an inch to 1 inch (1.3-2.5cm) of rain this time of year, but this week many areas could see between 4 and 8in (10 and 20cm), with even more in the mountains, National Weather Service meteorologist Mike Wofford said.

More wind and heavy snow was expected in the Sierra Nevada, where gusts created “near white-out conditions” and made mountain pass travel treacherous.

Governor Gavin Newsom declared emergencies in six counties to allow state assistance.

The state deployed resources and first responders to several coastal and southern California counties, and the California national guard was on standby.