As early-season floods continue to hammer the Midwest, nearly two-thirds of U.S. states are at risk of seeing waters rise significantly this spring, and 25 are facing moderate or major events, according to the National Oceanic and Atmospheric Administration’s 2019 Spring Outlook, which the agency released last week.
Idaho—in particular the Wood River Valley—falls into the latter camp. NOAA forecasts a “greater than 50 percent” chance of moderate flooding in the central portion of the state between March and May, with minor flooding possible elsewhere.
In agency parlance, “moderate” flooding translates to “some” inundation of buildings and roads near waterways, and “some” evacuation of people and property to higher ground. “Minor” flooding means little to no property damage, but potential public risk—think water on a roadway.
Flood risk is determined by a calculus of factors including snowpack levels, soil moisture, frost depth, precipitation and surrounding streams, but local influences can change it quickly.
“In the western U.S., snowpacks at higher elevations may continue to build over the next month, and the flood risk will depend on future precipitation and temperatures,” NOAA said in a statement.
On Tuesday, the snow-water equivalent, a measure of liquid in the snowpack, was 127 percent of median across the Big Wood Basin, according the federal Natural Resource Conservation Service. The Little Wood Basin stood at 137 percent.
Meanwhile, floodwaters have already ravaged the middle of the country.
“The extensive flooding we’ve seen in the past two weeks will continue through May and become more dire,” Ed Clark, director of NOAA’s National Water Center in Tuscaloosa, Ala., said during the news conference. “This is shaping up to be a potentially unprecedented flood season, with more than 200 million people at risk for flooding in their communities.”