SAN FRANCISCO — A powerful storm churned down the West Coast Thursday, bringing strong gales and much-needed rain and snow that caused widespread blackouts in Northern California and whiteouts in the Sierra Nevada. The brunt of the storm hit the San Francisco Bay Area, flooding freeways, toppling trees and keeping thousands of people home from work and school. "It's a big storm, as we expected, and it's headed south with very powerful winds and heavy rainfall," said National Weather Service meteorologist Will Pi.