Widespread Spring Flooding Likely, NOAA says

By Andrew Freedman

Nearly half of the United States is threatened with flooding this spring, the National Weather Service (NWS) announced today. The areas most at risk for major or record-breaking flooding include the Upper Midwest down into parts of western Illinois and eastern Iowa, as well as portions of the Northeast, according to the agency’s new spring outlook.

“For the third consecutive year, the stage is set for potential widespread, record flooding in the North Central United States,” says Jack Hayes, director of the National Weather Service, which is part of the National Oceanic and Atmospheric Administration (NOAA). For example, in St. Paul, Minn., there is a 95 percent chance of major flooding, as well as a 50 percent chance of record-breaking flooding, Hayes says.

NOAA's spring flood outlook, showing a large area at risk of flooding. Credit: NOAA.

Forecasters are most concerned about communities such as Fargo, N.D., and St. Paul, where severe flooding has occurred in recent years and the combination of an unusually deep snowpack and above average precipitation in the coming weeks is likely to bring yet another major flooding event. The water content in some parts of the North Central states is currently ranked among the highest in the last 60 years, Hayes says.

The rivers that forecasters say are most prone to flooding include the Red River, which comprises the border between eastern North Dakota and northwest Minnesota, the Milk River in eastern Montana, the Minnesota River, and the upper Mississippi River basin from Minneapolis southward to St. Louis, among others.

“Many metropolitan areas have a greater than 95 percent chance of major flooding, including Fargo, Grand Forks, St. Paul, Davenport, Rock Island, Sioux Falls and Huron,” according to a NOAA news release. Also, NOAA gives an 80 percent chance that Devils Lake in North Dakota will reach two feet above last year’s record level of 1452.1 feet.

How quickly temperatures warm during the spring, along with the amounts of any additional precipitation that may fall from storm systems, will help determine the magnitude, timing and extent of any flooding, NOAA says.

NOAA’s spring outlook for April through June shows higher odds of above-average temperatures and below average precipitation across the southern U.S., and below average temperatures from the Pacific Northwest to the northern Plains. The drier than average conditions from Florida, along the Gulf Coast, and westward to the Southwestern states is projected to exacerbate existing drought conditions that have contributed to a recent spate of wildfires.

Spring drought outlook, showing persisting drought across the southern states and into the Mid-Atlantic. Credit: NOAA Climate Prediction Center.

“From the Southwest, across the South and northward to the mid-Atlantic, drought has been spreading and deepening since the winter and is forecast to persist in spring. Wildfires will be an increasing threat, especially when humidity is low and when winds are high,” NOAA states.

The spring outlook takes into account the weakening of La Niña conditions in the equatorial tropical Pacific Ocean. La Ni

ña, which is characterized by cooler than average water temperatures in this region, tends to have the most influence on winter weather, bringing wetter than average conditions to the Pacific Northwest and Ohio Valley, and drier and milder winters in the South. Ed O’Lenic of the Climate Prediction Center in Maryland says La Ni

ña peaked in December and January, and is projected to be gone within the next month or two. However, its effects will linger in some places, particularly in the Pacific Northwest where a cool early spring can be anticipated, he says.

La Niña is a natural source of climate variability, and works on separate timescales and via different mechanisms than global climate change from emissions of greenhouse gases such as carbon dioxide. Whereas La Niña tips the odds in favor of certain conditions, particularly across North America in wintertime, global climate change alters the likelihood of a wide variety of weather and climate variables worldwide, and its influence is not limited to one or two seasons.