Heavy rain, rapid thaw to raise flood risk in Upper Midwest this week

By Alex Sosnowski, AccuWeather senior meteorologist

A storm set to bring a major blizzard to the High Plains will pump warm air with rain northward and raise the risk of flash flooding over the Upper Midwest at midweek.

While some sporadic rainfall is likely from Tuesday to Wednesday, the heaviest rainfall in many areas may occur during Wednesday night to Thursday.

Milder air in absence of heavy rain will tend to soften up the snow cover during the first part of this week. Temperatures will climb into the 30s and 40s F.

However, as heavier rain hits with surging mild air combined with a gusty wind, some of the snow may rapidly melt and lead to flooding. Temperatures in some areas where there is snow on the ground may climb well into the 40s and 50s.

"The greatest risk of flooding will tend to be in urban and poor drainage areas where piles of snow are blocking storm drains," according to AccuWeather Senior Meteorologist Kristina Pydynowski.

Download the free AccuWeather app to stay alert to the latest forecast and flood advisories as they are issued.

"Efforts to clear a path for water to get to the storm sewers should be done in advance of the storm," Pydynowski said.

Motorists should anticipate delays and blocked roads due to flooding in cities such as Minneapolis, Rochester and Duluth, Minnesota; Eau Claire, La Crosse and Wausau, Wisconsin; Ironwood and Marquette, Michigan; Sioux Falls, South Dakota; Des Moines and Mason City, Iowa; and Omaha, Nebraska.

The area of concern for the north-central United States is likely to extend from eastern and central Nebraska to southern and eastern Minnesota, much of Wisconsin and the Upper Peninsula of Michigan.

In addition to the likelihood of urban flooding will be the potential for roof collapses.

RELATED: 
What you should do if you get stuck driving in floodwaters 
Dangerous storms to aim for Texas, Oklahoma to Arkansas this week
Blizzard to bombard central US as bombogenesis takes place this week 
AccuWeather 2019 US spring forecast

The 1-3 inches of rain forecast to fall on part of the North Central states will tend to be absorbed by the deep snow cover. The depth of the snow on the ground ranges from a few inches to a few feet over much of the region.

Satellite imagery shows the extensive snow cover in the north-central U.S. (Satellite/NOAA)

Where there remains deep snow on flat roofs, the sudden added weight gain can trigger a failure or collapse of the structure.

Flash flood risk this week may be just the start of major flooding this spring

As the spring progresses, the vast area of deep snow on the ground over parts of the North Central states has the potential to lead to significant river flooding, as well as widespread flooding of poor drainage areas.

Rainfall farther south has already contributed to significant flooding along the Ohio and Mississippi rivers. This may be just the beginning of a long flood season for the Central states as snow melts and storms with rain come calling,