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Vast areas of the United States are at risk of flooding this spring, even as Nebraska and other Midwestern states are already reeling from record-breaking late-winter floods, federal scientists said on Thursday.

Nearly two-thirds of the lower 48 states will have an elevated risk of some flooding from now until May, and 25 states could experience “major or moderate flooding,” according to the National Oceanic and Atmospheric Administration.

“The flooding this year could be worse than anything we’ve seen in recent years, even worse than the historic floods of 1993 and 2011,” said Mary C. Erickson, deputy director of the National Weather Service, in a conference call with reporters. The major flooding this month in Nebraska, Minnesota, Iowa and elsewhere is “a preview of what we expect throughout the rest of the spring,” she said.

Some 13 million people could be exposed to major flooding, making this a “potentially unprecedented” flood season, said Edward Clark, director of NOAA’s National Water Center.