Traffic drives through flooded lanes on Highway 101 in South San Francisco, Calif., Saturday, Dec. 31, 2022. AP
In the high Sierra Nevada, as much as 2 feet (0.6 meters) of snow could accumulate Saturday into early Sunday. The National Weather Service in Sacramento warned about hazardous driving conditions and posted photos on Twitter showing traffic on snow-covered mountain passes, where vehicles were required to have chains or four-wheel drive.
The so-called atmospheric river storm was pulling in a long and wide plume of moisture from the Pacific Ocean, and flooding and rock slides triggered by the storm closed portions of roads across northern California.
The California Highway Patrol said a section of U.S. 101 _ one of the state's main traffic arteries _ was closed indefinitely south of San Francisco because of flooding. Videos on Twitter showed mud-colored water streaming along San Francisco streets, and a staircase in Oakland turned into a veritable waterfall by heavy rains.
Weather service meteorologist Courtney Carpenter said the storm could drop over an inch of rain Saturday in the Sacramento area before moving south. One ski resort south of Lake Tahoe closed chair lifts because of flooding and operational problems, and posted a photo on Twitter showing one lift tower and its empty chairs surrounded by water.
``We're seeing a lot of flooding,'' Carpenter said.
The Stockton Police Department posted photos of a flooded railroad underpass and a car that appeared stalled in more than a foot (30 centimeters) of water.
The rain was welcomed in drought-parched California, but much more precipitation is needed to make a significant difference. The past three years have been California's driest on record.
A winter storm warning was in effect into Sunday for the upper elevations of the Sierra from south of Yosemite National Park to north of Lake Tahoe, where as much as 5 feet (1.5 meters) of snow is possible atop the mountains, the National Weather Service said in Reno, Nevada.
A flood watch was in effect across much of Northern California through New Year's Eve. Officials warned that rivers and streams could overflow and urged residents to get sandbags ready.
Some rainfall totals in the San Francisco Bay Area topped 4 inches (10 centimeters).
The state transportation agency reported numerous road closures, including Highway 70 east of Chico, which was partially closed by a slide, and the northbound side of Highway 49, east of Sacramento, which was closed because of flooding. In El Dorado County, east of Sacramento, a stretch of Highway 50 was closed because of flooding.
Humboldt County, where a 6.4 magnitude earthquake struck on Dec. 20, also saw roadways begin to flood, according to the National Weather Service's Eureka office. A bridge that was temporarily closed last week due to earthquake damage may be closed again if the Eel River, which it crosses, gets too high, officials said.
It was the first of several storms expected to roll across California over the next week. The current system is expected to be warmer and wetter, while next week's storms will be colder, lowering snow levels in the mountains, said Hannah Chandler-Cooley, a meteorologist at the National Weather Service in Sacramento.
The Sacramento region could receive a total of 4 to 5 inches (10 to 13 centimeters) of rain over the span of the week, Chandler-Cooley said.
``Strong winds could cause tree damage and lead to power outages and high waves on Lake Tahoe may capsize small vessels,'' the weather service in Reno said.
Avalanche warnings were issued in the backcountry around Lake Tahoe and Mammoth Lakes south of Yosemite.
On the Sierra's eastern front, flood watches and warnings continue into the weekend north and south of Reno, Nevada, where minor to moderate flooding was forecast along some rivers and streams into the weekend.
In Southern California, moderate-to-heavy rain was falling Saturday. The region will begin drying out on New Year's Day and the Jan. 2 Rose Parade in Pasadena should avoid rainfall.
Another round of heavy showers were forecast for Tuesday or Wednesday, the National Weather Service in Oxnard said.