First atmospheric river of the season forecast to soak San Francisco Bay Area
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People shield themselves from a rainfall in Chinatown in Oakland, California on Jan. 4, 2021. A cold front passing through the San Francisco Bay Area included high winds and brief periods of intense rainfall.Douglas Zimmerman/SFGATE
The biggest storm of the season so far is expected to soak the San Francisco Bay Area Tuesday into Thursday, with rainfall amounts in urban areas ranging from two to four inches.
Meteorologists are calling the system an atmospheric river, a wet storm pulling a long plume of water vapor in the atmosphere — 250 to 375 miles wide on average — and often referred to as a river in the sky. On the West Coast, atmospheric rivers most often originate in the South Pacific, and as they travel from the tropics across the ocean, they collect incredible amounts of moisture.