A massive spring snow melt in the Upper Midwest is about to begin this week, and flooding will likely occur over a much larger area than typically occurs each spring, says Steve Buan, Service Coordination Hydrologist, North Central River Forecast Center (NCRFC), Chanhassen, MN.

“The bottomland areas from St. Paul to St. Louis will certainly see floodwaters this year,” he says. “How badly the flooding will be depends on early April rainfall amounts.”

Flooding is likely to peak in St. Paul, MN, about the first week of April, and continue down the Mississippi, where it should peak in St. Louis about the end of April, adds Buan. The good news is that flooding will come earlier this year than in other flood years, he points out, so there may be time for some areas to dry before planting time.

The bad news is how widespread and severe the flooding might be. “For southern and western Minnesota, there’s a substantial snow pack yet to melt – about 4-6 in. of water,” says Buan. “While Iowa is pretty much free of snow right now, a lot of the water melting from Minnesota is going to pass through Iowa and down the Mississippi River.”

Wisconsin also has a large amount of snow that is likely to begin melting this week. As a result, Buan says the NCRFC is “forecasting spring flooding, probably about like 2008, or even higher, depending on rainfall.”

The current weather forecastis for a few days of warmer temperatures, followed by some light rain in Minnesota and Wisconsin this week, “but nothing too heavy,” says Steve Hilberg, director, Midwestern Regional Climate Center, Champaign, IL. “After some warm temperatures for a couple days, it should cool off again for a bit,” he says. “However, next week looks like it will bring a more active weather system that could produce some heavy rain.”

The worst case scenario for flooding in the region would be to have heavy showers over the current snow pack, combined with very warm temperatures, points out Hilberg. “It doesn’t look like there will be a huge, sudden warm up, but the potential for some major flooding is still there,” he says. “It would only take one big rain event that could wash all that snow away.”

Moderate flooding is already going on along the Ohio River and also along the Mississippi River in southern Missouri, notes Hilberg. “So far, March precipitation has been less than 50% normal for a lot of areas west of the Mississippi River and over twice normal for a lot of the region east of the Mississippi River,” he adds. “That’s why there’s already been flooding going on in the Ohio River Valley this week, but most of Iowa and northern Missouri is fairly dry right now.”

Still, the likelihood for more Midwest flooding in March and April is relatively high given the large amount of snow that could melt this week or next in Wisconsin and Minnesota, and already saturated soils in other parts of the Midwest, adds Hilberg. “For now, it looks like much of the Upper Midwest is probably going to see some weather delays for spring fieldwork and planting,” he says. “How widespread the delays might be in much of the Corn Belt will largely depend on how much rainfall occurs during the next several weeks.”