Music fans in Colorado weren't expecting torrential downpours as they lined up to see Steely Dan in concert.
Video shows water gushing down the stairs of the Red Rocks Amphitheater in Morrison.
Rain, hail and flooding forced everyone to take cover. It delayed, yesterday's concert by about half an hour.
Steely Dan took the stage once the storm passed.
VIDEO: Flooding, hail delays Steely Dan concert in Colorado