A powerful winter storm system was moving across California on Thursday, toppling trees, knocking out power and bringing more rain, wind and snow to the already battered state.

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The storm, one of several that is expected to pound the West Coast this month, moved on shore from the Pacific Ocean overnight,

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whipping across San Francisco with heavy rain and high winds and bringing heavy snow in the Sierra Nevada.

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On Thursday morning, flash flood watches and winter storm warnings covered large swaths of the state, and about 600,000 residents were under high wind warnings.

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Forecasters cautioned that a combination of high winds and saturated ground conditions could topple trees, leading to power outages

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As of Thursday morning, about 170,000 customers were without electricity in the state, according to the tracking site poweroutage.us.

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