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A massive line of fierce storms forecast to wallop the Midwest and Mid-Atlantic on Wednesday and Thursday has meteorologists warning about the possibility of a derecho.

So what exactly is a derecho, and why is it so dangerous?

A derecho is a widespread, long-lived wind storm associated with a band or shelf of rapidly moving thunderstorms.

By definition, a derecho has to be at least 240 miles long and have winds of at least 58 miles per hour. However, meteorologist Howard Bernstein says many classic derechos have winds that can top 100 miles per hour, causing extensive damage, leading to massive power outages and toppling tons of trees.

The now infamous 700-mile derecho last June that roared into Washington, D.C., topped 100 miles per hour .

To learn more about how a derecho forms, check out the video above.