The storm from the Gulf of Alaska brought the first significant rainfall to the region in several weeks, the National Weather Service said.
Periodic showers, including hail, hit the Bay area in time for the morning commute while a batch of new snow fell in the Sierra Nevada, where ski resorts around Lake Tahoe were expecting up to 8 inches of snow.
Dozens of cars were either stuck in the snow or involved in accidents near the rural community of Sonora, the California Highway Patrol said. About 50 to 75 vehicles became stranded or were in collisions on Highway 49 and nearby roadways when it started snowing heavily in the Sierra Nevada foothills, said CHP Lt. Scott Clamp.
"Travelers were just not prepared," Clamp said. There were a handful of minor injuries, but no major injuries, he said.
Snow flurries were spotted high in the hills in Oakland and in neighboring Berkeley, said Rick Canepa, a weather service meteorologist in Monterey. The top of Mt. Hamilton near San Jose and the tips of Mt. Diablo in the East Bay also got a dusting.
In the Sacramento area, a tornado with wind speeds between 40 to 70 mph was spotted north of Red Bluff shortly after 1:30 p.m., according to the weather service.
More rain was forecast for the Bay area and for parts of Southern California. Authorities warned of hazardous conditions for drivers on mountain and interior valley roads into early Wednesday, when the storm was expected to move east.
Even though San Francisco saw highs in the 70s last week, California has had a colder-than-normal winter overall.
"We went from about 10 degrees above normal this past weekend to 10 degrees below today," said Austin Cross, another weather service meteorologist based in Monterey. "We're usually somewhere in the 60s, temperature-wise, at this time of year."
San Francisco has gotten nearly 14 inches of rain since October, or about 85 percent of its normal rainfall during the fall-winter season, Cross said. Oakland received 83 percent and San Jose had about 80 percent, he added.
Associated Press writer Shaya Tayefe Mohajer in Los Angeles and John S. Marshall in San Francisco contributed to this report.