SoCal Weather

Slow-Moving Winter Storm to Unleash Rain and Snow in Southern California

Downpours that could trigger debris flows in burn area are possible Thursday and Friday when the heaviest rain is expected in Southern California.

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What to Know

  • A storm fueled by a river of moisture in the sky is expected to bring rain and snow to Southern California.
  • The rain will start Thursday and continue into Friday.
  • Downpours are possible, a major concern for SoCal's recent wildfire burn zones.

An atmospheric river is fueling a storm expected to bring two days of rain, snow and downpours that could unleash debris flows in Southern California’s wildfire burn areas. 

Winter storm warnings and flash flood watches are in effect for a widespread part of Southern California as the storm moves slowly down the coast. It is Southern California's third storm in the last seven days after a mostly dry winter.

In Riverside County, evacuation warnings were issued for the Apple and El Dorado burn scar areas, where residents were asked to be prepared for possible downpours that could trigger debris flows. A voluntary evacuation order was issued by the Orange County Sheriff's Department for residents near the Bond Fire burn area.

A flash flood watch was issued for the recent burn areas in LA County, including the Bobcat, Lake, and Ranch2 fire areas. Flood watches also were issued in Orange, Riverside and San Bernardino counties.

The low-pressure system gathered strength off the Oregon coast, and will likely remain mostly stationary through Thursday morning. Rain fell steadily Wednesday in San Luis Obispo County, where the system remained largely stalled.

The storm will enter Los Angeles County and other parts of Southern California Thursday afternoon with the heaviest rain expected Thursday night and into Friday.

Atmospheric rivers are like rivers in the sky. They're behind some of California's wettest winters. NBC4 forecaster Anthony Yanez shows how they work.

The storm had already dropped nearly 14 inches of rain in some parts of San Luis Obispo County over 36 hours. The storm was pushing slowly south, with rain expected to fall in Ventura County by early evening.

"At 8 p.m., we find ourselves in LA County with some heavy rain, and that leading edge of the rain will be heading into the IE and Orange County," said NBC4 forecaster Belen De Leon. "Tomorrow morning, we’re waking up to some wet roads and snow in the mountains."

A winter storm warning goes into effect at 3 p.m. Thursday and continues into Friday afternoon for most of SoCal. The warning also was in effect for Orange, Riverside and San Bernardino counties.

When storms bring high rainfall rates, SoCal's burn scarred hillsides are under threat. Belen De Leon explains why Thursday Jan. 28, 2021.

What makes this storm different from previous storms this winter is that it’s fueled by an atmospheric river, a long plume of moisture in the sky over the Pacific. It can act likes a conveyor belt, delivering days of rain to California. The weather phenomenon is associated with some of California’s most damaging storms and wettest winters.

The region could see flood warnings as the storm moves closer, and residents in flood-prone areas will likely be urged to be prepared to evacuate at a moment's notice.

Residents in the Yucaipa area are under evacuation orders ahead of the storm. Christine Kim reports for the NBC4 News at 11 a.m. on Thursday Jan. 28, 2021.

“By Saturday, we could be seeing rain amounts of 1.5 to 3 inches,” said De Leon.

One to 3 feet of snow could accumulate at elevations above 6,000 feet.

Heavy snow was falling Wednesday during a blizzard in the Sierra Nevada Mountains. Statewide snowpack is 41 percent of average. Last year at this time, California was a 73 percent of average. 

"Things are about to change, and it's all because of this atmospheric river storm," De Leon said.

Winds will blow at 20 to 30 mph, with gusts ranging up to 50 mph. A wind advisory will take effect in the county's mountains at 3 a.m. Wednesday and continue until 3 p.m. Thursday. Forecasters said the strongest winds are likely in the San Gabriel Peaks and the Grapevine area, making driving difficult, especially for high-profile vehicles.

Los Angeles County health officials have issued a cold weather alert through Thursday for the mountains and Antelope Valley, and through Tuesday for the Santa Monica Mountains and the Santa Clarita Valley.

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