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A windstorm that swept across Kansas, Missouri and Illinois in May 2009 was so fierce that it has earned a brand-new name: super derecho.

A derecho (from the Spanish adverb for "straight") is a long-lived windstorm that forms in a straight line - unlike the swirling winds of a tornado - and is associated with what's known as a bow echo, a line of severe thunderstorms. The term "derecho" was first used over a century ago to describe a storm in Iowa. Across the United States there are generally one to three derecho events each year.

The May 8, 2009, derecho, however, was in a league of its own. An intense vortex and eye-like structure similar to what forms at the center of tropical cyclones (the generic name for tropical storms and hurricanes) appeared in the bow echo, said study team member Clark Evans of the National Center for Atmospheric Research, in Boulder, Colo.