LOS ANGELES (AP) - Foothill areas below the fire-scarred Angeles National Forest were barricaded with sandbags and concrete barriers Monday as the first in a wave of storms brought a threat of mudslides.
The National Weather Service predicted a cold storm from Canada would bring an inch or two of rain in most areas of Southern California, with up to 4 inches in some locations.
The heaviest rain, accompanied by strong winds, was expected to begin in the late afternoon.
Elsewhere, the hills east of San Francisco Bay saw a rare overnight dusting of snow, with snow also predicted for Fresno and other Central Valley communities.
Up to a half-inch of snow fell overnight around Danville near the base of Mount Diablo east of San Jose.
In the Central Valley, California's agricultural heart, Modesto residents also woke up to the unusual sight of snow. A hard freeze was expected with lows in the upper 20s.
Several roads in the San Gabriel Mountains, a few miles northeast of Los Angeles, were closed because of concerns that as much as three-quarters of an inch of rain an hour could fall, sweeping rocks and mud from slopes left naked by the huge Station Fire earlier this year.
The summer blaze burned 250 square miles of forest and 89 homes.
Light rain caused several nonfatal accidents, including several involving jackknifed big-rigs, that snarled the region's morning commute.
Sandbags and temporary concrete barriers have been in place since September on some foothill streets. More were erected late last month, when a smaller storm passed through and caused minor flooding. Some of the barriers were decorated with Christmas garlands.
Residents of foothill towns such as La Canada Flintridge were urged to be ready to quickly evacuate.
"Certainly if you see any debris coming down your streets, our advice is to just get in your car and go down the mountain," Bob Spencer of the Los Angeles County Department of Public Works told Fox News.
In the mountains, the storm could bring 1 to 2 feet of snow while falling as low as 1,500 feet, forecasters said.
In San Bernardino County, the Rim of the World and Bear Valley school districts declared a snow day and closed schools.
In San Diego, the National Weather Service issued a warning of high winds. Gusts up to 60 mph were forecast.
Two storms from the tropical Pacific were expected to arrive on Thursday and Saturday.