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SACRAMENTO (AP/KTXL) — A potent atmospheric river barreled toward California on Tuesday, bringing the threat of downpours that could unleash destructive debris flows from wildfire burn scars and a heavy dump of snow in the Sierra Nevada.

An evacuation warning was issued for part of Solano County, where there was a potential for mud and debris flow and flash flooding in the LNU Lightning Complex burn scar.

The National Weather Service office in Sacramento tweeted that snow was expected as low as 500 to 2,500 feet in the Sierra on Tuesday, then higher to 3,000 to 4,000 feet by Thursday mornings. It warned of whiteout conditions on Sierra roads, along with the possibility of downed trees and tree branches, as well as road closures.

The heaviest snowfall is expected Tuesday evening into Wednesday.

Caltrans said traveling in the Sierra after sunset is not advised.

Heavy rain and wind was expected in the valley, with forecasters predicting three inches of rain in Sacramento beginning Tuesday afternoon.

Evacuation orders were in effect for areas of fire-scarred Santa Cruz County and evacuation warnings were issued in San Mateo County.

“If you have not already heeded local county advice, don’t wait any longer. This morning is the time to act and prepare if you’re near a burn area,” the National Weather Service office for the San Francisco Bay Area wrote.

The atmospheric river — a huge plume of moisture extending over the Pacific — was expected to be preceded by lighter prefrontal rain before intensifying Tuesday evening, hitting the North Bay first, then spreading south to Santa Cruz, Monterey and Big Sur.

“Overnight rain late Tuesday and early Wednesday is expected to meet or exceed thresholds for potential debris flow events,” Santa Cruz County tweeted.

Debris flows — torrents carrying massive boulders, soil, trees and other objects — are considered more dangerous than mudslides or landslides. The Jan. 9, 2018, debris flow that blasted the Santa Barbara County community of Montecito killed 23 people.

Meanwhile, icy conditions in mountains north of Los Angeles shut Interstate 5 in Tejon Pass and State Route 58 in Tehachapi Pass early Tuesday.