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What’s behind record flood predictions?

More than a third of the U.S. faces a high risk of flooding this spring, and Midwesterners may get the brunt of it, according to government forecasters.

More than a third of the U.S. faces a high risk of flooding this spring, and Midwesterners may get the brunt of it, according to government forecasters.

Heavy rains last fall, thaw from an unusually wet winter, and a potentially wet spring due to El Nino could produce record flooding in some areas, the National Oceanic and Atmospheric Administration (NOAA) announced late Tuesday.

“We are looking at potentially historic flooding,” said NOAA administrator Jane Lubchenco. “It’s a terrible case of déjà vu, but this time the flooding will likely be more widespread,” she said, referring to the record floods of 2009 in Fargo, N.D.’s Red River valley.

The upper Midwest, including the Dakotas, Minnesota, and Iowa, has the highest risk for flooding.

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Residents in Fargo, N.D., and Moorhead, Minn., are sandbagging homes and reinforcing dikes and levees as the Red River continues to rise. It is forecast to crest Saturday about 20 feet above flood stage. The river crested at 22 feet above flood stage in 2009, setting an all-time record, according to NOAA.

Flood risk is also above-average throughout much of the Mid-Atlantic, south, and the east coast, including the Mississippi River and Ohio River basins.

A combination of factors contribute to this year’s higher-than-average flood risks, says Scott Dummer, a hydrologist at NOAA’s North Central River Forecast Center.

“It’s a multiyear problem,” says Mr. Dummer. “We’ve been in an extreme wet pattern since this fall.”

The wet fall weather saturated the ground, limiting drainage just as winter snows began to fall, says Dummer. A barrage of storms dumped record snows across the Mid-Atlantic and east coast this winter, and December precipitation was four times the average in the Midwest, says NOAA.

“The East coast had its share of precipitation-makers, lots of big storms this winter,” says Dummer. “And throughout the country, we had heavy, wet snow that contained a lot more water.”

That heavy snow has given way to unusually warm spring in some areas, particularly the upper Midwest, accelerating spring thaws and causing rivers to surge and flood.

“With rivers and streams beginning the spring thaw season at high levels, combined with a significant amount of water held in the snow pack, conditions are ripe for flooding this Spring,” NOAA reported in its assessment.

Adding to the water woes, forecasters predict El-Nino will bring “wetter than average conditions in coastal sections of the southeast,” increasing flood risks in states like Louisiana, Mississippi, and parts of Florida and Georgia.

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Flooding is the deadliest weather hazard, claiming about 100 lives each year, according to NOAA.