The "bomb cyclone" storm that bloated rivers as it roared through much of the Midwest last week combined with spring snowmelt Sunday to drive some Midwest rivers to record levels and forced people in hundreds of homes to evacuate.
At least two deaths were blamed on flooding. Two other men have been missing for days.
Some areas must brace for more rain Tuesday, forecasters said.
Tuesday's storm won't match last week's "bomb cyclone" that triggered heavy snow, howling winds and several tornadoes, AccuWeather meteorologist Jim Andrews said. But he said up to another inch of rain could fall on areas that have no place to put the water.
"That could trigger new or aggravate problems if that rain targets the areas hit hardest by the flooding," he said.
The governors of Nebraska, Iowa and Wisconsin have declared states of emergency. Roads and highways were closed. Amtrak said some trains in the region were delayed and other canceled.
Overall, as of Monday morning, about 9 million people in some 14 states live where a flood warning is in effect, the National Weather Service said.
The Missouri River between Omaha and Kansas City could remain at or near record levels through most of this week as runoff from flooded streams and rivers flows downstream, AccuWeather said.
In Nebraska, Offutt Air Force Base was under siege from the rising water. Base officials finally called off a furious sandbagging effort, saying the water was rising too fast to be stopped.
Much of the base, home to almost 9,000 service members, was underwater Sunday. It was open to essential personnel only.
"We have about 2 feet of water in the Bennie Davis Maintenance Facility," 55th Wing Commander Col. Michael Manion said. "All streets south and east of the Field House are impassible."
Interstate 29 was shut down from Omaha to Rockport, Missouri. Last week, Columbus, Nebraska, farmer James Wilke, 50, died when a bridge collapsed as he used a tractor to rescue a stranded motorists.
"All evacuation notices, suggested and mandatory, are strongly encouraged," the Nebraska Emergency Management Agency said. "By ignoring evacuation recommendations, extraction requests made later may be delayed."
Fast moving water was approaching the town of Thurman, IA. This is likely the result of levee breeches in the area. Evacuation operations were beginning for the town. #iawx
— NWS Omaha (@NWSOmaha) March 17, 2019
More than 2,000 Iowans have fled their homes since heavy rains triggered flooding last week. The Missouri River in Fremont County, Iowa, rose two feet above its previous record level on Sunday. Authorities ordered evacuation of the town of Thurman's more than 200 residents.
"Fast moving water was approaching the town of Thurman," the National Weather Service warned Sunday. "This is likely the result of levee breaches in the area. Evacuation operations were beginning."
County Emergency Management Director Mike Crecelius said the swift current added to the danger.
“This wasn’t a gradual rise,” Crecelius said. “It’s flowing fast and it’s open country – there’s nothing there to slow it down.”
Aleido Rojas Galan, 55, died after he and two other men tried to drive around a "road closed" barricade, Fremont County Sheriff Kevin Aistrope said Saturday. All three escaped the vehicle, and Galan was found clinging to a tree in the water.
Galan was flown to a Nebraska hospital where he died. The other men were treated for their injuries.
Parts of Missouri, Minnesota, South Dakota and Wisconsin were also facing flooding. Several Wisconsin communities have been evacuated since Friday night.
"The massive flooding impacting our state can be overwhelming," Gov. Tony Evers said.
Contributing: Doyle Rice, USA TODAY; The Associated Press
This article originally appeared on USA TODAY: Thousands flee record Midwest flooding triggered by 'bomb cyclone' – and more rain is coming