National forecasters and emergency managers warned Tuesday that the Upper Midwest faces a second spring of "potentially historic flooding" with the melting of snow and ice from El Niño-driven winter storms.

Administrator Jane Lubchenco of the National Oceanic and Atmospheric Administration called it "a terrible case of déjà vu, but this time the flooding will likely be more widespread."  The agency issued a map showing above-average flood risk extending over a third of the country.

Flooding already is underway or imminent in the lower Red River basin in North Dakota and South Dakota and along several rivers in Iowa, including parts of the mainstem Mississippi and the lower Illinois River.  Mayor Frank Cownie of Des Moines — a city still recovering from floods in 2008 — told a news conference that the Raccoon and Des Moines rivers already are above flood stage and some levees were being inspected "on an hourly basis."

While the threat to the upper Midwest is obvious, National Weather Service director Jack Hayes said forecasters were not as confident about developing flood potential elsewhere.  "In the South and East, where an El Niño-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."

Louis Uccellini, director of the National Centers for Environmental Prediction, said flood predictions beyond the midwest were muddled by two sources of weather forecasting uncertainty.  The first obstacle is what forecast modelers refer to as the "spring wall" — a time when atmospheric circulation is in a state of especially sensitive and unpredictable transition.  The second factor, he noted, is that the El Niño is weakening, which means forecasters can't rely on its continuing influence to shape weather patterns in the weeks ahead.

Officials characterized the circumstances in the Red River basin as "extremely unusual."  Hydrologist Scott Dummer observed that in 110 years of recorded flood conditions in the Red River Valley "we have never seen back to back spring floods."