Two die in car and rare snow forecast for Seattle as storms batter western US

Two people have died in a submerged car, evacuations have been ordered for wildfire-scarred California, and Seattle and Portland face the rare chance of snowy streets as a wave of storms rolled through the western United States.

The new storms, which could drop rain and snow over much of the region into next week and plunge the Pacific Northwest into a lengthy cold snap, follow a now-departed atmospheric river that delivered copious amounts of precipitation this week.

In the Sierra Nevada, an evacuation warning was issued on Thursday for about 150 homes downstream of Twain Harte Lake Dam after cracks were found in granite that adjoins the manmade part of the 11-metre-high (36ft) structure.

The Sierra range could see 1.5- 2.4m (5-8ft) of snow through the holidays, with 3m (10ft) possible at higher elevations, and authorities urged people to avoid travelling through the mountain passes, which could be treacherous.

A winter storm warning issued on Friday remains in effect until 10am on Tuesday for most of the Sierra, where almost 1m (3ft) of snow had fallen by early Friday at Mammoth Mountain south of Yosemite national park. About 0.6m (2ft) fell on Thursday at some Tahoe-area ski resorts.

Wind gusts over ridges could exceed 100mph (160km/h), the National Weather Service said, making travel difficult to impossible.

In southern California, evacuation orders were issued on Thursday night in Orange county because of possible mudslides and debris flows in three canyons where a wildfire last December burned the ground bare. The local fire authority reported a mudslide on Thursday night in one canyon that affected some roads but no injuries were reported.

On Thursday, a slow-moving front dumped the most rain and snow parts of eastern Nevada have seen on the date in more than a half century.

In preparation for freezing temperatures, snow and ice in the Pacific Northwest this holiday weekend and next week, state officials in Oregon declared an emergency and shelters were being opened throughout the region to help the homeless.

Recent forecasts show at least an inch of snow was likely to fall on Sunday in the Seattle and Portland regions, which do not typically see snow.

But forecasters and state officials said the main concern was cold temperatures in the region, with daytime highs next week struggling to reach above freezing, that are likely to impact people experiencing homelessness and those without adequate access to heating.

Oregon governor Kate Brown issued a state of emergency declaration on Thursday evening to remain in effect through to 3 January, saying expected snow and sustained temperatures below freezing could result in critical transportation failures and disruptions to power and communications infrastructure.

Portland and Multnomah county earlier declared states of emergency.