A small tornado tore tree limbs and ripped awnings as a powerful band of thunderstorms moved through Northern California during the latest deluge to swell rivers and prompt evacuations over flood fears.

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The tornado was on the ground for about 3/8 of a mile just south of Sacramento late Tuesday, National Weather Service meteorologist David Rowe said.

No injuries were reported from the twister, which was about 100 yards wide and registered on the low end of the tornado scale.

The twister got the attention of forecasters at the weather service's Sacramento office.

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"It came as a little bit of a surprise considered that we're so focused on all the heavy snow and rain," Rowe said, adding that the Sacramento area received about 2 inches of rain Tuesday.

Meteorologists in the Northwest received their own storm surprise. A major snowstorm spread through Portland, Oregon, and southwest Washington, toppling trees, closing schools, cutting power to thousands. Parts of Portland got more than a foot of snow, a rare event in a city known for its rain.

The intensity of the storm came as a surprise to meteorologists, most of whom expected no more than 4 inches.

"We are going to be analyzing this one, because this is a special one," National Weather Service meteorologist Treena Jensen said.

While the heaviest downpours have moved through Northern California, and rivers are expected to recede throughout the day, the risk of flooding remains from runoff and showers predicted to continue into Thursday.

About 2,000 people in Wilton, a rural community near Sacramento, were asked to leave their homes Tuesday evening, as emergency crews worked to try to bolster a Cosumnes River levee.

Sacramento County emergency services official Mary Jo Flynn said officials were monitoring in case water spills over the levee. Low-lying buildings are at risk of inundation but Flynn pointed out many of the homes along the path of a possible flood are built on berms or sit on higher ground.

An evacuation center opened in neighboring Elk Grove but some residents said they plan to stay put.

"We have no concerns," Lill Nichols, who with her husband runs a horse farm near the river, told the Sacramento Bee. "We have animals and can't evacuate anyway."

A blizzard warning remains in effect at Lake Tahoe, with a half-foot of snow forecast for Wednesday. Unexpected rain has prompted more flooding in parts of northern Nevada, including Reno, Sparks and Carson City.

Several ski resorts in parts of the Sierra planned to stay shuttered for a second day Wednesday, including Squaw Valley and Alpine Meadows, which has no power due to the storm. The resort posted on Facebook on Wednesday that it had received more than 3 feet of snow in the last 24 hours.

The Russian River in California rose again under pounding rain, placing some 3,000 Sonoma County residents under an evacuation advisory. 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 Tuesday 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."

People were evacuated in downtown San Anselmo, north of San Francisco, 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.

In Southern California the second fast-moving storm this week dumped steady rain. Officials warned residents along Los Angeles-area hillsides scarred by wildfires of the possibility of mudslides, but only minor debris flows were reported.

The storms were the latest of back-to-back systems that have brought the heaviest rain in a decade to parts of Northern California and Nevada.

A series of storms already has added 33 billion gallons of water to Lake Tahoe since Jan. 1.

The storms are part of an "atmospheric river" weather phenomenon that draws precipitation from the Pacific Ocean as far west as Hawaii.

In Colorado, several passes are closed so crews can trigger slides Wednesday to make them safe as more snow falls in the mountains. The avalanche danger remains high.