Powerful storms swept through parts of Northern California on Saturday, knocking down trees, causing widespread power outages and prompting weather officials to issue what they said was the first-ever tornado warning for San Francisco.

Inclement weather plagued areas of the U.S., with dangerous conditions including heavy snow in upstate New York, a major ice storm in Midwest states and severe weather warnings around Lake Tahoe.

San Francisco residents were woken up by a tornado warning early Saturday morning during a powerful storm system that battered the region with heavy rain and wind.