SACRAMENTO, Calif. — A powerful storm brought torrential rain or heavy snow to much of California on Saturday, clogging traffic and closing roads as the state prepared to usher in a new year.

High in the Sierra Nevada, up to 2 feet of snow could accumulate through early Sunday morning. The Sacramento National Weather Service warned of dangerous 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 carrying a long, wide column of moisture from the Pacific Ocean. Flooding and rock slides closed parts of highways in Northern California.

“Too many road closures to count at this time,” the weather agency in Sacramento said in an afternoon tweet. Sacramento County urged residents of the unincorporated community of Wilton to evacuate, warning that flooded roads could «cut off access to leave the area.»

Rainfall in downtown San Francisco on Saturday topped 5 inches by midafternoon, making it the second-wettest day on record, after a November 1994 deluge. If the rain continues to fall, it could threaten the record for almost three decades.

The California Highway Patrol said a section of US 101, one of the state’s main traffic arteries, was closed indefinitely south of San Francisco due to flooding. Videos on Twitter showed mud-colored water running down the streets of San Francisco, and a stairway in Oakland turned into a veritable waterfall from heavy rain.

Weather service meteorologist Courtney Carpenter said the storm could dump more than an inch of rain on the Sacramento area before moving south. A ski resort south of Lake Tahoe closed chair lifts due to flooding and operational issues, posting a photo on Twitter showing a lift tower and its empty chairs surrounded by water.

“We are seeing a lot of flooding,” Carpenter said.

The Sacramento agency published a map of 24 hour precipitation through Saturday morning, showing a wide range of totals in the region, from less than an inch in some areas to more than 5 inches in the Sierra foothills.

Mammoth Mountain Ski Area reported numerous lift closures, citing high winds, poor visibility and ice.

The Stockton Police Department released photos of a flooded railroad underpass and a car that appeared to be stuck in more than a foot (30 centimeters) of water.

The rain was welcome in drought-parched California, but it takes a lot more precipitation to make a significant difference. The past three years have been California’s driest on record.

A winter storm warning was in effect through Sunday for the upper elevations of the Sierra from Yosemite National Park south to Lake Tahoe north, where up to 5 feet of snow is possible at the summit. of the mountains, reported the National Weather Service. said in Reno, Nevada.

A flood watch was in effect for much of Northern California through New Year’s Eve. Authorities warned that rivers and streams could overflow their banks and urged residents to prepare sandbags.

Some rainfall totals in the San Francisco Bay Area exceeded 4 inches.

The state transportation agency reported numerous road closures, including Highway 70 east of Chico, which was partially closed by a landslide, and the north side of Highway 49, east of Sacramento, which was closed due to flooding. In El Dorado County, east of Sacramento, a section of Highway 50 was closed due to flooding.

Humboldt County, where a magnitude 6.4 earthquake struck on December 20, also saw roads begin to flood, according to the Eureka office of the National Weather Service. A bridge that was temporarily closed last week due to earthquake damage could be closed again if the river Eel, which it crosses, rises too high, authorities said.

It was the first of several storms expected to hit California over the next week. The current system is expected to be warmer and wetter, while next week’s storms will be cooler, said Hannah Chandler-Cooley, a meteorologist with the National Weather Service in Sacramento.

The Sacramento region could receive a total of 4 to 5 inches of rain during the week, Chandler-Cooley said.

“High winds could damage trees and lead to power outages and high waves on Lake Tahoe can capsize small boats,” the weather service in Reno said.

Avalanche warnings were issued for the countryside around Lake Tahoe and Mammoth Lakes south of Yosemite.

On the eastern front of the Sierra, flood watches and warnings were issued over the weekend north and south of Reno, Nevada, where light to moderate flooding was forecast along some rivers and streams.

In southern California, moderate to heavy rain was falling on Saturday. The region will begin to dry out on New Year’s Day and no rain is expected during Monday’s Rose Parade in Pasadena.

Another round of heavy rain is forecast for Tuesday or Wednesday, the National Weather Service in Oxnard said.