The latest round of storms in California created punishing travel conditions across the state on Saturday, with icy roads snarling traffic in the Sierra Nevada mountains and downpours cutting off roadways south of San Francisco along the Central Coast.
By Saturday afternoon, mountain highways had closed several times after cars and trucks lost control and spun out in the high winds and heavy snow. In warmer parts of California, ground that was still saturated from the previous two weeks of storms created the conditions for mudslides and flooding.
“During the height of the storms, stay home and watch the football games or relax,” said Gilbert Mohtes-Chan, a spokesman for California’s Department of Transportation, or Caltrans, in an interview on Saturday.
Driving conditions were especially treacherous in the northeastern part of the state. Late Saturday morning, the National Weather Service said it was “dangerous to impossible” to travel in Sierra Nevada because of whiteout conditions.
Earlier in the day and overnight, portions of major highways that cross the mountains, including Interstate 80 and Route 50, were closed several times because of vehicle spinouts and whiteout conditions. As of 12:30 p.m. Pacific, part of Interstate 80 was closed because of low visibility and a section of Route 50 was closed for avalanche control.
At lower elevations, flooding, landslides and downed trees and power lines cut off roads.
In Santa Cruz, California Highway Patrol warned people not to drive unless it was necessary and said that threats included fallen wires and trees, flooding, sinkholes and slides. About 50 miles south of San Francisco in the coastal town of Pescadero, a mudslide caused a road to close indefinitely and a nearby one partially collapsed.
Areas burned by wildfires were especially vulnerable to the heavy rains, including about 60 miles northwest of Sacramento in Rumsey Canyon, where a highway was closed on Saturday because of a landslide. Mr. Mohtes-Chan said that heavily burned areas were vulnerable to slides because the burned layer of the ground can be hard and shell-like. When looser soil above the hard layer becomes saturated with water, it can slip out.
Floods and mudslides were also a concern in Southern California, though the storm conditions on Saturday were less severe than in Northern and Central California.
Mr. Mohtes-Chan said that people who have to travel should prepare for and be aware of the conditions, which could include traffic delays, flooding and blowing snow. Caltrans has an online map that shows live traffic conditions.
He also warned drivers to stay on main roads, even if navigation apps such as Waze or Google Maps advise drivers to use seemingly less busy and more rural roads. “There have been people who get stuck in the snow, and then the cell service is spotty and they are stuck stranded because they went off the main routes,” Mr. Mohtes-Chan said.