A late winter storm on Wednesday caused widespread flooding and snarled travel in the Nebraska, Iowa, Colorado and Wyoming, forcing evacuations in some areas.
Blizzard conditions and flooding closed numerous roadways in the region. Nearly 1,400 flights were canceled at Denver airport, where all runways were shut down.
Colorado declared a state of emergency and National Guard troops were activated.
National Guard troops in Nebraska were put on alert for possible activation, as emergency officials braced for the storm to intensify overnight there.
"This has the potential to be a very severe weather event," Nebraska Governor Pete Ricketts said.
"We're already seeing flooding in a number of communities and evacuations in several communities."