Many San Diegans were awakened by light but steady rain as a storm front swept across the county early Wednesday.

“Once the front passes, it opens the screen door and allows rain to take place and that’s really what has happened,” NBC 7 Meteorologist Jodi Kodesh said.

Rain droplets fell overnight, making roads slick across San Diego County. Click here to view NBC 7's Interactive Radar.

Conditions should be breezy at the coast and in the valleys while windy in the mountains.

Expect showers to become a little more widespread, mid-morning, and then taper this afternoon. Tomorrow’s storm is more potent, and may bring thunderstorms, Kodesh said.

In Northern California, authorities urged thousands of people to leave their homes as rivers swollen by four days of heavy rain threatened to crest above flood level.

About 2,000 people in Wilton, southeast of downtown Sacramento, left their homes Tuesday evening, as emergency crews and officials worked to try to bolster a Cosumnes River levee in Sacramento County. The river was projected to overflow its banks Wednesday morning.

A winter storm brought rain to San Diego on Wednesday. NBC 7’s Elena Gomez reports on the conditions from Encinitas in the North County.

In Sonoma County, some 3,000 residents were under an evacuation advisory 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."

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North of San Francisco, people were evacuated Tuesday evening from businesses and homes in downtown San Anselmo after a rain-swollen creek broke its banks. The Corte Madera Creek was flowing 1 foot over flood stage, the Marin County Sheriff's Office said.

Tuesday's storm was the latest of back-to-back systems -- buffered by a brief respite Monday -- that have brought the heaviest rain in a decade to parts of Northern California and Nevada. More showers were forecast for Wednesday morning.

A blizzard warning was in effect for parts of the Sierra Nevada, the first issued in the past nine years, said Scott McGuire, a forecaster for the National Weather Service based in Reno, Nevada.

"This is definitely a dangerous, life-threatening situation going on up there," he said. "People should not attempt to travel at all."

Forecasters warned of up to 10 feet of snow in the highest mountains, with up to 7 feet of snow around the resorts of Lake Tahoe, high risk of avalanches, and wind gusts to 60 mph. The Sierra ridge had gusts of more than 100 mph.

Many ski resorts shut down Tuesday because of the storm. A number of main roads in the Sierra were closed, including Interstate 80, or required chains.

Nearly 3 feet of new snow already was reported Tuesday morning at the top of the Mount Rose ski resort between Reno and Lake Tahoe. A series of storms already has added 33 billion gallons of water to Lake Tahoe since Jan. 1.

NBC 7’s Liberty Zabala reports on the shelters opening in time to allow San Diego’s homeless to get shelter from the storm expected to arrive later this week.