SAN FRANCISCO — Winter arrived early in Northern California with wind, rain and snow that was expected to intensify Monday as forecasters warned that mountain passes will probably be closed to traffic and areas burned by wildfires could face rockslides and mudslides following an especially warm and dry fall across the U.S. West.

The multiday storm, a powerful “atmospheric river” weather system that is sucking up moisture from the Pacific Ocean, raised the threat of flooding and was expected to dump more than 8 feet (2.4 meters) of snow on the highest peaks in California and Nevada and drench other parts of the two states before it moves on midweek, forecasters said.

“This is a pretty widespread event,” said National Weather Service meteorologist Anna Wanless in Sacramento. “Most of California, if not all, will see some sort of rain and snow.”

The storm will bring much needed moisture to the broader region that’s been gripped by drought that scientists have said is caused by climate change. The latest U.S. drought monitor shows parts of Montana, Oregon, California, Nevada and Utah are classified as being in exceptional drought, which is the worst category.

Most western U.S. reservoirs that deliver water to states, cities, tribes, farmers and utilities rely on melted snow in the springtime.

This week’s storm is typical for this time of the year but notable because it’s the first big snow that is expected to significantly affect travel with ice and snow on the roads, strong winds and limited visibility, Wanless said.

Drivers on some mountain passes on Sunday had to put chains on their tires and were warned of possible road closures in coming days.

“Travel will be hazardous and is highly discouraged,” the weather service office in Sacramento said on Twitter. Heavy rain could cause minor flooding and rockslides, especially in areas that scarred by wildfires, forecasters said.

Gusts were so strong in and around San Francisco that state transportation officials issued a wind advisory for the Bay Bridge that connects the city with Oakland and warned drivers of campers and trailers to avoid the 4.5-mile (7.2-kilometer) span late Sunday.

South of the San Francisco Bay Area, a 40-mile (64-kilometer) stretch of the iconic Highway 1 in California’s Big Sur area was closed as a precaution until Tuesday. The scenic coastal route frequently experiences damage during wet weather.

Nearby Monterey County residents who live close to burn scars from last year’s Dolan Fire were warned to be prepared to evacuate if rains loosen hillsides and cause debris flows.

In Southern California, the San Bernardino County sheriff’s department issued evacuation warnings for several areas, citing the potential for flooding, and Los Angeles County fire officials urged residents to be aware of the potential for mud flows.

Forecasters said strong winds accompanying the storm could lead to power outages. Karly Hernandez, a spokesperson for Pacific Gas & Electric, said crews and equipment are staged across the state to respond quickly if the power goes out.

The second storm predicted to hit California midweek shortly after the current storm moves on could deliver almost continuous snow in mountainous areas, said Edan Weishahn of the weather service in Reno, which monitors an area straddling the Nevada state line.

Donner Summit, one of the highest points on Interstate 80 and a major commerce commuter route, could face major travel disruptions or road closures, Weishahn said.

The weather follows a November that was unseasonably warm for California.

Vail Resorts’ three Tahoe-area ski resorts opened with limited offerings over the weekend after crews produced artificial snow. Spokeswoman Sara Roston said the resorts are looking forward to more of the real thing.

The Sierra Avalanche Center warned heavy snow and strong winds on top of a weak snowpack could cause large and destructive avalanches.

One man died Saturday in a backcountry area of the Crystal Mountain ski resort in Washington state when he was caught in an avalanche that temporarily buried five others.

———

Weber reported from Los Angeles.