A mountain pass across the Sierra Nevada that runs through Yosemite National Park was closing to traffic Thursday ahead of storms expected to dump up to 2 feet of snow on the highest peaks, park officials said.
In fire-scarred regions of Northern California's wine country, meanwhile, crews were working to stem the flow of ash, soil and hazardous substances into waterways in case the storms bring heavy rains there.
Tioga Road, the soaring eastern entry to Yosemite, was closing to traffic shortly before nightfall Thursday. Officials also were closing Glacier Point Road, which offers sweeping views of Yosemite Valley.
Both roads are to be shut through Monday, when the storms are expected to dissipate and road conditions can be assessed.
Light rain over the northern mountains is expected as early as Thursday afternoon. But heavier rain and snow likely will fall Friday night through Saturday, with a second storm coming Sunday, the National Weather Service said.
In Sonoma County north of San Francisco, crews have been working long days to prevent feared mudslides and water pollution in areas hit by last month's devastating wildfires, which killed at least 43 people and destroyed more than 8,900 homes and other structures.
The work includes placing sandbags and bundles of straw to block runoff into streams, and moving to capture some of the runoff in urban areas that burned. California has declared a public-health emergency in fire areas in part out of concern that household chemicals from burned areas could contaminate soil and water.
This weekend, up to 2 feet of snow is forecast to fall in elevations above 8,000 feet, and at least a foot of snow is expected in Donner and Tioga passes and other areas above 6,000 feet, forecasters said. The storms coming in from the Gulf of Alaska also will bring rain to the San Francisco Bay Area, including North Bay counties still recovering from last month's fires.
The first storm will clear by Sunday afternoon, but a second storm system is expected to hit the area Sunday night.
So far, the only Lake Tahoe-area ski resort open is Mt. Rose area on the Nevada side. But operators were pleased with the forecast.