The driver of a semitractor-trailer gathers his belongings after it was involved in an early morning crash along the eastbound 60 freeway in Riverside, Calif., on Monday morning, Jan. 9, 2017. A massive storm system moved through Southern California Monday with heavy rain and minor flooding. (Stan Lim/The Press-Enterprise via AP)
The driver of a semitractor-trailer gathers his belongings after it was involved in an early morning crash along the eastbound 60 freeway in Riverside, Calif., on Monday morning, Jan. 9, 2017. A massive storm system moved through Southern California Monday with heavy rain and minor flooding. (Stan Lim/The Press-Enterprise via AP) Credit: STAN LIM

Guerneville, Calif. — Authorities asked thousands to flee a rural Northern California community where flood water threatened to burst over an overwhelmed levee on Tuesday as four days of storms brought the heaviest rain and snow in years and locked the Sierra Nevada mountains in a rare blizzard.

Emergency crews and officials worked through Tuesday to try to bolster the levee located in Sacramento County along the Cosumnes River, before deciding to ask 2,000 residents of Wilton to voluntarily evacuate before dark fell.

Sacramento County emergency services official Mary Jo Flynn said water was expected to spill over the levee before midnight, covering low-lying roads and buildings with up to 1 foot of floodwater.

In the city of Sacramento, workers wrenched open more than a half-dozen century-old spill gates on the state’s biggest river, the Sacramento, on Tuesday to ease pressure on the swollen river and on levees there.

Some 3,000 Sonoma County residents remained under an evacuation order as the Russian River rose again under pounding rain. Officials red-tagged seven homes, ordering residents out, when a rain-soaked embankment came crashing down.

Johna Peterson was one of few residents who ventured out in the remote Sonoma County town of Monte Rio. Walking on the bridge across the Russian River, Peterson worried about what the coming hours and days would bring.

“I think it’s going to go higher,” Peterson said. “There’s nowhere for this water to go.”

Tuesday’s storm was the latest of back-to-back systems — buffered by a brief respite on Monday — that have brought the heaviest rain in a decade to parts of Northern California and Nevada.

The storms are part of an “atmospheric river” weather phenomenon that draws precipitation from the Pacific Ocean as far west as Hawaii. Its impact can be catastrophic.