Forecast: Flood risk for third of U.S.

More than a third of the contiguous United States faces a high or above average flood risk this spring, the National Weather Service reported Tuesday.

"We are looking at potentially historic flooding in some parts of the country this spring," Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, said at a news briefing while presenting the government's spring outlook. NOAA oversees the weather service.

The highest threat is in the Dakotas, Minnesota and Iowa. Those areas have already seen some flooding and rivers are rising quickly, especially the Red River between North Dakota and Minnesota.

"Crests could approach the record levels set just last year" along the Red, the service stated. In 2009, about 100 homes in the area were damaged and thousands of people were evacuated after the Red River rose above the flood stage for a record 61 days and crested twice.

"It’s a terrible case of deja vu, but this time the flooding will likely be more widespread" across the Midwest, Lubchenco said.

"As the spring thaw melts the snowpack, saturated and frozen ground in the Midwest will exacerbate the flooding of the flat terrain and feed rising rivers and streams," she added.

Above flood stage in Iowa
Des Moines, Iowa, is among the region's cities on watch.

Attending the NOAA briefing, Mayor Frank Cownie said his city, still recovering from previous flooding, has closed off some low-lying roads and is bringing in extra pumps "just in case" the Des Moines and Raccoon rivers flood.

Both are above flood stage and, so far, protected by levees. Recent ice jams among the Raccoon have caused it to rise as much as three feet in just a few minutes.

The forecasters said an El Nino weather pattern was one of the reasons for the wet winter and spring. El Nino causes an abnormal warming of waters in the equatorial Pacific and can alter weather patterns worldwide.

Factors that play into "imminent" Midwest flooding, NOAA said, include:

• A snowpack more extensive than in 2009 and containing more than 10 inches of liquid water in some areas;
• Milder temperatures since mid-March that speed up snow melt and runoff;
• Above normal streamflows;
• December precipitation that was up to four times above average;
• Ground that is frozen to a depth as much as three feet below the surface.

The current snowpack is among the top 10 since World War II, with much of it remaining on the ground because of the earlier cold weather, said Jack Hayes, director of the National Weather Service. As a result, rivers in the Midwest are likely to remain above flood stage for weeks or more.

Above average risk in South, East
The South and East are also more susceptible to flooding, the weather service said.

"In the South and East, where an El Nino-driven winter was very wet and white, spring flooding is more of a possibility than a certainty and will largely be dependent upon the severity and duration of additional precipitation and how fast existing snow cover melts," said Hayes.

In addition, NOAA’s Climate Prediction Center said odds currently favor:

• Wetter-than-average conditions in coastal sections of the Southeast;
• Warmer-than-average temperatures across the western third of the nation and Alaska;
• Below-average temperatures in the extreme north-central and south-central U.S.

The Associated Press and Reuters contributed to this report.