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Derecho May Spread High Winds From Fargo to Minneapolis, Chicago


By Kristina Pydynowski, Senior Meteorologist
July 21, 2014; 6:49 AM


Heat and humidity building across the North Central states will fuel potentially damaging thunderstorms over a broad area through Tuesday.

A storm system emerging from the Rockies will fuel severe thunderstorms in a west-to-east fashion from the Dakotas to the western Great Lakes Monday afternoon through Tuesday.

Severe thunderstorms will first erupt around Fargo and Bismarck, North Dakota, and Aberdeen and Watertown, South Dakota, on Monday night and then will race to St. Cloud, Duluth and Minneapolis, Minnesota.

The greatest threat from the storm setup will be high winds that can cause property damage, knock out power and down scores of trees.

According to Severe Weather Expert Henry Margusity, "It is possible the complex of storms develops into a derecho."

A derecho is defined by the Storm Prediction Center as producing damaging winds along a swath of at least 240 miles.

Some communities may also be hit by large hail, flooding downpours and a short-lived tornado.

AccuWeather.com meteorologists are especially concerned for widespread damaging winds in the corridor from the eastern border of the Dakotas to the Minneapolis and Duluth areas.

The severity of the thunderstorms will decrease somewhat Tuesday morning, but flooding and blinding downpours and gusty winds will still be a concern across northern Wisconsin. Heavy rain will also pour down across the Upper Peninsula of Michigan and into central Ontario.

A new line of severe thunderstorms will then erupt to the south and east later Tuesday from around the northern part of Lake Michigan to Iowa.

Cities in Tuesday's threat zone include Green Bay, Milwaukee and Madison, Wisconsin, and Waterloo, Cedar Rapids and Davenport, Iowa.

Violent thunderstorms will then continue pressing to the south and east into the Lower Peninsula of Michigan, northern Illinois and northern Missouri Tuesday evening and into the night. Chicago lies in the threat zone.

"It is possible the second complex of storms develops into a derecho or possibly brings high winds and damage over a sizable swath," Margusity said.

The Tuesday evening commute is most at risk in Chicago and Milwaukee. As the storms roll through, there is the risk of a ground stop and substantial flight delays.

A key ingredient to the impending severe weather danger across the northern Plains and Upper Midwest is the building heat and humidity that will bring some communities the hottest weather so far this summer.

The heat comes on the heels of the record chill that caused the start of the recent week to feel more like September or early October than the middle of July.

After the high of 65 F last Monday set a record for the day's coolest high temperature, Minneapolis is set to have its hottest day of the year. Through July 20, the highest the temperature has been at the Twin Cities is 90 degrees.

The passage of the severe weather will open the door for more comfortable air to return to the North Central states for midweek. A repeat of the record chill from last is not in the offing.

As that occurs, AccuWeather.com meteorologists expect the severe weather danger to shift to the Ohio Valley and eastern Great Lakes on Wednesday then the southern mid-Atlantic and Carolinas on Thursday.