Spring flooding has already been disastrous, and it's likely to get worse, federal forecasters announced Thursday. Floods could reach "unprecedented" and "potentially historic" levels.

Almost the entire eastern two-thirds of the nation should see flooding this spring, National Weather Service deputy director Mary Erickson said at a news conference on Thursday. Some 25 states are forecast to see "moderate" to "major" flooding, the weather service said.

The Midwest floods are “a preview of what we expect throughout the rest of the spring,” she said. "The flooding this year could be worse than what we have seen in previous years ... even worse than the historic floods we saw in 1993 and 2011," Erickson added.

Start the day smarter:Get USA TODAY's Daily Briefing in your inbox

The deadly, destructive flooding that began last week from Minnesota to Missouri has killed at least four people, caused more than $1.5 billion in estimated losses and damages and destroyed more than 2,000 homes.

Scientists said this month's flooding was caused by rapid snow melt combined with heavy spring rain and late-season snowfall in areas where the ground was already saturated. Much of the precipitation fell during the "bomb cyclone" that whipped the region last week.

"This is shaping up to be a potentially unprecedented flood season, with more than 200 million people at risk for flooding in their communities," said Ed Clark, director of NOAA's National Water Center in Tuscaloosa, Alabama.

Catastrophe:Before and after satellite images show destruction in Nebraska and Iowa after Midwest floods

The water that's now soaking the Upper Midwest will eventually make its way down the Mississippi toward the Gulf Coast, where flooding will worsen in May.

“The extensive flooding we’ve seen in the past two weeks will continue through May and become more dire and may be exacerbated in the coming weeks as the water flows downstream,” Clark said.

Forecasters say the biggest risks include all three Mississippi River basins, plus the basins of the Red River of the North, the Great Lakes, the eastern Missouri River, the lower Ohio River, the lower Cumberland River and the Tennessee River.

Global warming:The waters are rising, the floods are coming. What are we doing to save ourselves?

Record-breaking:Historic, deadly Midwest floods are worst 'anybody has ever experienced' in some areas

It’s still too early to determine if human-caused climate change played what, if any, role in the flooding. However, scientists said the conditions are consistent with what they expect from global warming.

“You can think of climate change as steroids for these rain events,” Texas A&M University climate scientist Andrew Dessler said.

As for the spring weather forecast, meteorologists said the East Coast and Northwest should see warmer-than-average temperatures from May through June. However, the central and northern Plains should stay unusually cool.

For rainfall, nearly the entire nation east of the Rockies should see a soggier spring than usual, with the Southeast and the central Rockies seeing the wettest conditions. The only unusually dry spot will be the Pacific Northwest.

Federal meteorologists do not issue forecasts for severe weather, which includes tornadoes, high winds and large hail.

Contributing: The Associated Press