Avalanche warnings as Sierra hit by major snowstorm; 4-5 feet expected this week

Higher elevations of Northern California were hit by heavy snowfall overnight, prompting avalanche warnings, as the region braced for a week of intense weather.

The National Weather Service said it expected 4 to 5 feet of snow in some Sierra areas and encouraged drivers to avoid mountain roads. One location, Kingsvale, got 23 inches of snow in just the last 24 hours.

The Sierra Avalanche Center on Monday issued a warning for some areas hit by heavy snow. “Human triggered wind slab avalanches occurred yesterday in a variety of locations. The ongoing combination of new snow and wind will keep this problem ongoing today,” the group said.

The northern half of the state has already seen impressive rains this fall and winter, filling reservoirs and replenishing the Sierra snowpack, a key source of water for California cities and farmlands.

A storm system is expected to bring rain and snow throughout the week in Northern California, and a foot of snow is expected Tuesday in the Sierra Nevada with an additional foot or two predicted for Wednesday, said Johnnie Powell, a weather forecaster with the National Weather Service.

“This is what we’re supposed to be getting,” Powell said. “After six years of a drought, I love saying that. This is normal rain and snow that we’re supposed to be getting in December and January.”

That same system might bring much-needed moisture to Southern California by the middle of the week. But that’s just a precursor to a bigger storm, NWS meteorologist Joe Sirard said.

The main event, a stronger storm system, is expected to move into the Los Angeles County area late Saturday and continue until Monday.

“There is the potential that if the main moisture feed into Southern California lines up over Ventura and L.A. counties, we could be under the gun for many inches of rain,” Sirard said.

Steady rain since the fall has pulled 15% of the state — all of it up north — out of drought conditions, according to the National Weather Service and the U.S. Drought Report.

But while Northern California has begun to rebound from the drought, Southern California remains dry.

Los Angeles marked a sober milestone last year, when the NWS announced that the last five years were the driest ever documented in downtown L.A. since official record-keeping began almost 140 years ago. Precipitation during that period totaled just 38.79 inches — roughly half the normal amount.

But December turned out to be a boon for Southern California, with a series of storms dumping decent amounts of rain and snow. It ended up being the wettest December since 2010.

State officials have said it’s far too early to declare the six-year drought over, though they acknowledge the improvements in Northern California.

In late December, officials said the Sierra Nevada snowpack was at 72% of normal. They expect that number to increase in the coming weeks.

Northern California’s improving fortunes help Southern California’s drought picture — but only to a point. Though Southern California still gets some water from the Sierra, about 50% of its supply comes from local sources such as groundwater and reservoirs.

December’s conditions and cold temperatures across the state have provided a winter wonderland view in both Southern California and the Bay Area, with mountain peaks getting strong dustings of snow.

The Grapevine was closed for periods in recent weeks because of heavy snowfall, and some motorists were temporarily stranded on mountain roads.

For more California breaking news, follow @AngelJennings. She can also be reached at angel.jennings@latimes.com.

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UPDATES:

10:24 a.m.: Updated with additional maps.

9:05 a.m. Jan. 3: Updated with new developments and snow conditions.

This article was originally published at 7:41 p.m. Jan. 2.