Dangerous storms to threaten northern Plains, Great Lakes

After rounds of thunderstorms rumbled across parts of the northern Plains on Thursday, unleashing damaging winds in the process across Montana and the Dakotas, AccuWeather meteorologists say the threat for severe weather will cover a much larger area into the weekend.

"A storm system will move into the northern Plains from the northwest, causing strong to severe thunderstorms to erupt as the weekend gets underway," said AccuWeather Meteorologist Jessica Storm.

A ripple in the atmosphere combined with an advancing cold front will aid in the development of thunderstorms into Friday night. The warmth and humidity in place ahead of the storms will add extra energy to any storms that form.

Thunderstorms that initially develop across the central Dakotas and northwestern Minnesota are then forecast to progress into central Minnesota, southwestern Ontario, northwestern Wisconsin and the Upper Peninsula of Michigan Friday night. Multiple hazards will be present with these storms.

"Storms can bring flooding downpours, hail and damaging winds with an AccuWeather Local StormMax™ of 90 mph from Friday afternoon through the night," Storm said.

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The National Weather Service's Storm Prediction Center indicates that nearly 10 million are facing the risk of severe weather across the northern Plains and Upper Midwest. Of those, nearly 2 million are facing a slight risk of severe weather, which is the fourth highest threat level on the SPC's outlook.

This map from the Storm Prediction Center shows the threat level for severe weather across the northern Plains and Upper Midwest on July 23, 2021.

The fact that the storms will continue into the night will be concerning for a couple of reasons. First, most people in the eastern portion of the threat zone are likely to be asleep when the thunderstorms move through. Therefore, residents will want to make sure they have a way to be alerted if a warning is issued.

The other danger is for anyone who will be traveling.

"Due to heavy rain, low-lying areas can experience flash flooding on roadways. Motorists should never drive on a flooded road," Storm said.

It is often difficult to gauge the depth of water at night. Due to this potential threat, forecasters advise motorists to turn around and find an alternate route anytime water covers the roadway. As little as a foot of swiftly-moving water can lift some vehicles.

To begin the weekend, the volatile weather will move farther to the east. Some of the storms from Friday night may continue into Lower Michigan on Saturday morning. However, even as those weaken while moving farther to the east, new storms are likely to develop late Saturday afternoon and dive southeastward on Saturday evening. This could impact some of the larger population centers of the Midwest, such as Chicago and Detroit.

Although flooding rainfall will be possible, especially in areas where multiple storms occur, the rain will fall in some drought-stricken areas, according to the United States Drought Monitor. The drought monitor is updated weekly, and the latest version shows exceptional drought in parts of North Dakota. Exceptional drought is the most intense type of drought according to the Drought Monitor, but parts of South Dakota, Minnesota, southern Wisconsin and northern Illinois are experiencing severe to extreme drought.

The front will continue to the east on Sunday. Locations such as Columbus, Ohio; Pittsburgh and State College, Pennsylvania; and Albany and Binghamton, New York may be in line for severe weather to round out the weekend. Storms that develop on Sunday are likely to move to the East Coast by Sunday night. The severe threat should be lower by the time the thunderstorms reach the Atlantic Seaboard, forecasters say.

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