High winds, intense snowfall and a weak snowpack combined to create dangerous conditions, the Sierra Avalanche Center advisory said. It recommended that skiers stay out of avalanche terrain.
The storm has dropped visibility to a quarter-mile or less on Interstate 80, forcing Caltrans to require chains and impose a 30 mph speed limit from Colfax to 11 miles east of the Nevada state line.
The first big storm arrived late in the season but brightened the state's water outlook heading into spring.
"It's nothing we haven't faced before. Just not this year," said Caltrans spokesman Rochelle Jenkins.
The National Weather Service said the snow level had dropped to 3,000 feet in the northern Sierra Nevada. Snow fell at the rate of one inch each hour, and forecasters expected at least eight more inches into Thursday. Winds gusted to 50 mph.
Sunny skies were expected through the weekend.
"Skiers can go have all of the fun they want on the weekend. It worked out perfectly," said Johnnie Powell, a forecaster with the National Weather Service in Sacramento. "It should be plowed out and there should be plenty of fresh powder."
So far I-80, the main east-west highway through the Northern Sierra Nevada, has remained open, except for brief periods to clear spinouts, Jenkins said.
Single-axle trucks pulling double trailers were being turned back, even with chains, because of traction problems. All vehicles were required to use chains except those with 4-wheel drive and all-wheel drive with snow tires.
Schools in Nevada and El Dorado counties were closed because of the snow.
Strong winds and heavy rain made for difficult driving conditions on San Francisco Bay area roads. At least two bridges -- the San Mateo-Hayward Bridge and the San Francisco-Oakland Bay Bridge -- were under a high-wind advisory. Caltrans said travel wasn't recommended for big-rigs, motorhomes and drivers pulling trailers.
The Northern California storm could ease fears among the 29 agencies that depend on snowmelt delivered through the State Water Project that already are bracing for meager allocations. Some farmers on the west side of the San Joaquin Valley have been told to expect just half of the water they requested for the spring and summer growing seasons.
The biggest wallop of snow was expected above 6,500 feet, where accumulation could be between 2 and 4 feet, and up to 5 feet at the highest elevations.