Flood risk in Upper Midwest this week may signal beginning of a long spring season ahead

By Alex Sosnowski, AccuWeather senior meteorologist
March 14, 2019, 5:36:03 AM EDT

A storm bringing a major blizzard to the High Plains will pump warm air with rain northward and extend the risk of flooding, ice jams and roof collapses over the Upper Midwest this week.

Heavy rain that began over parts of the Plains on Wednesday spread northeastward into Thursday over the Upper Midwest.

US Midweek

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.

Widespread urban flooding is anticipated

"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.

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"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.

NC regional 3/14

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.

Early Wednesday morning, reports of flooding were just beginning with water over the roads in Hold and Garfield counties in central Nebraska. Isolated flooding was also reported in eastern Kansas.

By Wednesday midday, at least six more counties in eastern Nebraska were reporting flooded roadways. The north fork of the Elkhorn River, near Norfolk, Nebraska, was out of its banks and rising. Further flooding, some dangerous enough to prompt evacuations, occurred overnight Thursday.

Ice jams, river flooding are expected

In addition to the likelihood of flash flooding, ice jams and river flooding are also anticipated.

There remains a significant amount of ice on rivers over the northern Plains, Upper Midwest and over parts of the central Plains. As the surge of warmth and rain hit at the same time, the ice will break up and may lead to ice jams and flooding.

Where there is a few to several inches of snow on the ground, enough rain is likely to fall to completely wipe out the snowcover.

The extra water released by the melting snow is likely to cause river flooding from portions of Wisconsin and Illinois to parts of Iowa, Nebraska, Kansas and northern Missouri.

River Flooding 3 pm

Many rivers in this swath are expected to reach moderate to major flood stage. Multiple points along the West Nishnabotna River in western Iowa are projected to reach record high levels.

Some of the larger rivers in the region, such as the Missouri river along the Nebraska and Iowa border, may not crest until later next week.

Weight of snow, rain to be too much for roofs to handle

In addition to the likelihood of flooding will be an enhanced risk of roof collapses.

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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.

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,

AP Flooding 1993

Flooding that occurs this spring along the Mississippi and across the northern Plains and Upper Midwest in general may end up in the company of recent decades, such as from 2014, 2011, 2008 and 1993.

Abnormally strong flows on the Mississippi and Ohio rivers that persist into the early summer may affect the efficiency of barge traffic and the transportation of grains and goods.

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