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Atmospheric river of rain ready to drench Northern California

Atmospheric river of rain ready to drench Northern California
San Francisco's Golden Gate Bridge is seen through a rain-covered windshield in December. It didn't rain at all in San Francisco in January, but rain is hitting the city Friday, with heavier downpours drenching other parts of Northern California. (Justin Sullivan / Getty Images)

The tracks of the Pineapple Express, a nickname for a band of warm, wet Pacific air, are tracing over Northern California, where residents are expected to be soaked with rain through early next week.

“It acts like a river moving through the atmosphere, raining copiously on things below,” said National Weather Service forecaster Diana Henderson. “It’s going to cover everybody.”

The band of air, known as an atmospheric river, is expected to drench residents from the northern San Joaquin Valley to Sacramento with 1 1/2 to 6 inches of rain over the next five days.

The coastal mountains could get 50 mph wind gusts, Henderson said.

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The wet band of air is dubbed the Pineapple Express because it originates in Hawaii, Henderson said. After a January so dry it set records -- with exactly zero rainfall in San Francisco -- a cold-weather system in Alaska created a vacuum that pulled the Pineapple Express toward Northern California, Henderson said.

Other conditions are going to push the wet weather east toward the Sierra Nevada, where the annual snowpack is a vital source of California's water.

Unfortunately, the showers headed there this weekend are too warm to add significantly to the snowpack, said meteorologist Eric Kurth, also with the weather service.

"There will be some snow," he said. "It'll be beneficial; whatever we get is good, but the sheer area is relatively limited."

Snow levels aren't expected to drop below 8,000 feet. If it snowed as low as 5,000 feet, he said, that would be a huge help.

The last Pineapple Express to hit California was in mid-December, when a series of storms drenched Southern California and created floods and rockslides.

For breaking California news, follow @JosephSerna.

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