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.

For the first time in recorded history, downtown San Francisco was included in a tornado warning on Saturday as severe storms swept through the city, just one week after a tsunami warning triggered widespread panic in the region.

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.