As disastrous as the flood season has already been in the Plains and Midwest, it is likely to expand and become more severe, warned the National Oceanic and Administration, which released its spring outlook Thursday, March 21.

The historic flooding that has ravaged eastern Nebraska and other parts of the Midwest over the past week is just "a preview" of what may come next, officials told reporters Thursday.

"We expect the flooding to get worse and become more widespread," said Mary Erikson, deputy director of NOAA's National Weather Service. "The stage is set for record flooding now through May."

Erikson said the flooding "could be worse than anything we have seen in recent years" including the devastating floods in 1993 and 2011, considered among the worst in U.S. history.

Due to rivers levels that are already high, hefty snowpack in the northern plains and above normal soil moisture, "conditions are primed" for more flooding, said Edwark Clark, director of NOAA's National Weather Center.

"This is potentially an unprecedented flood season," Clark said. "It may become more dire in the coming weeks."

The outlook said 200 million Americans are at risk of experiencing flooding.

"The areas of greatest risk for moderate to major flooding include the upper, middle, and lower Mississippi River basins including the mainstem Mississippi River, Red River of the North, the Great Lakes, eastern Missouri River, lower Ohio, lower Cumberland, and Tennessee River basins," the outlook said.

Major flooding causes "extensive inundation of structures and roads," according to the National Weather Service, and frequently requires evacuation of low-lying areas.

The flood damage over the past week has cost $1.3 billion in Nebraska alone and has caused at least four deaths.

The Weather Service's Erikson described flooding as an "underrated killer" that leads to nearly 100 fatalities in an average year.

Clark said about two-thirds of the Lower 48 is likely to experience some sort of flooding this spring. Over outside the zone of greatest risk in nation's heartland, minor flooding, which can inundate roads and basements, is a risk east of the Mississippi River and in parts of California and Nevada, the outlook noted.

NOAA's Climate Prediction Center favors above normal precipitation during the April to June period over much of the middle of the nation, which will compound the flood risk. This follows a winter in which record precipitation fell in parts of the north central U.S., in some places 200 percent of normal.

The U.S. overall had its wettest winter in recorded history.

But perhaps a bigger threat than any precipitation in the pipeline is the water locked in the snowpack. In the eastern Dakotas and most of Minnesota, more than 20 inches of snow remains on the ground.

Over the next week, computer model simulations show that snowpack eroding, which will release large quantities of water into river systems intensifying flooding and ice jams.

As of Thursday, over 100 river and stream gauges in the Central U.S. indicated moderate to major flooding, and another 140 minor flooding.

"The extensive flooding we've seen in the past two weeks will continue through May ... and may be exacerbated in the coming weeks as the water flows downstream," said Clark.

NOAA officials as well as Daniel Kaniewski, acting deputy administrator at the Federal Emergency Management Agency stressed the importance of flood preparedness, including owning flood insurance in vulnerable areas, having a plan in the event of a flood, and a way to receive warnings.

This article was written by Jason Samenow, a reporter for The Washington Post.