SAN FRANCISCO — A windy storm sweeping down the West Coast knocked down trees, ripped through freeway and street signs, delayed hundreds of flights and knocked out power for thousands of people in California and Nevada.

Up to 10 inches of rain is expected this weekend in parts of the drought-stricken region, but the rainfall won’t make a significant dent in California’s historic drought.

Still, the storm is a welcome change after six dry weeks in the Bay Area. For the first time in recorded history, there was no measurable rainfall in downtown San Francisco in January, when winter rains usually come.

It would take 150 percent of the average rainfall for California to recover from the dry period, state water resource officials say. But snow is more important than rain because snowpack supplies about a third of the water needed by residents, agriculture and industry.

About 26 miles west of Seattle, an overflowing river inundated at least a half dozen homes on the Olympic Peninsula. Rescuers went door to door in Brinnon to check homes on a road partially blocked by a mudslide, Jefferson County Emergency Management spokeswoman Keppie Keplinger said.