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.

For the first time in recorded history, downtown San Francisco was issued a tornado warning on Saturday as severe storm conditions swept through the city, prompting local authorities to warn residents of the rare threat.

Less than two weeks after a tsunami warning, residents were jolted awake before 6 a.m. to consider a new potential disaster scenario.