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.

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.

A major ice storm has created treacherous driving conditions across Iowa and eastern Nebraska and prompted temporary closures of Interstate 80 after numerous cars and trucks slid off the road.