SACRAMENTO (AP/CBS13) – Rain and snow showers fell on Northern California on Wednesday in the first wave of a wet weather pattern that is expected to spread throughout the state and last through Christmas into next week, forecasters said.

Forecasters warned that holiday travel, especially through high passes, would be affected by multiple rounds of rain, mountain snow and gusty winds.

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Winter storm warnings were scheduled to go into effect in sections of the Sierra Nevada as early as Wednesday afternoon or by Thursday morning and last through Sunday, the National Weather Service said.

Chain requirements were already in effect for vehicles on some stretches of routes through the Sierra, according to the California Department of Transportation.

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Rainfall was light to moderate around the San Francisco Bay Area and was slowly spreading down the coast.

Widespread rain wasn’t expected in Southern California until Thursday. Forecasters said a flood watch would be in effect Thursday evening through Friday morning due to possible excessive rainfall from an atmospheric river pointed at the region.

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Copyright 2021 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.