The storms produced winds of up to 100 km / h while moving through Iowa and Illinois.
“Stay inside. Do not start moving loose items outside until the wind blows,” the Chicago National Weather Service office tweeted.
The storms are part of what the National Weather Service Storm Prediction Center called a “particularly dangerous situation.”
Tornado warnings are in effect west of agoikago.
More than 500,000 homes and businesses in the Midwest are without electricity, including one-third of all customers in Iowa.
“Strong PDS storm hours are rare and are reserved only for the strongest storm events,”; said CNN meteorologist Brandon Miller. “Windstorms are expected to reach up to 100 km / h with the hurricane line as it rolls through northern Illinois and southern Wisconsin.”
A 106 km wind gust in Marshall, Iowa, had already been reported as the storm passed.
A derecho (pronounced similar to “deh-REY-cho”) is a widespread, long-lived storm, which is accompanied by a band of rapidly moving showers or hurricanes.
This storm complex is within the same area that is also at a moderate risk (level 4 of 5) for major storms. The SPC improved this risk level on Monday afternoon due to the formation of the currency. The danger zone includes over 13 million people.
In addition to wind damage, tornadoes and large hailstorms – one and a half inches in diameter – are possible.
CNN Senior Meteorologist Dave Hennen contributed to this report.