Missouri Storm in a Class All Its Own

First posted on 09-09-2010

In June, Southwest Missouri witnessed a bizarre cloud formation that is still being reviewed by the World Meteorological Society as a potentially new form of cloud. Last year’s windstorm that swept across Kansas and into Missouri and Illinois earned the region another meteorological first. Winds were fierce enough to give that type of storm a new name: super derecho.

Derecho comes from the Spanish adverb for “straight.” As a weather event, a derecho describes a long-lived windstorm with strong straight-lined winds that develops a bow echo and is associated with severe thunderstorms. The straight-line winds in a derecho are different from the circular winds in a tornadic event. The term “derecho” was first used early in the 20th Century to describe an Iowa storm. Only one to three of these storms occur each year.

On May 8, 2009, a derecho of incredible strength and magnitude developed an intense vortex and a structure that resembled the eye formed in tropical storms. That derecho increased in strength as it roared across Kansas and slammed into Southwest Missouri with wind speeds of 70 to 90 miles per hour, and spawning 18 tornadoes. The super derecho cut a 100 mile wide path through Missouri and struck Illinois with 90 to 100 mile per hour winds. The system finally fell apart just before entering Indiana.

“We are currently in the process of determining how the super derecho developed and evolved, seeking to understand how and why it became so strong as compared to other derecho events,” said team member Clark Evans of the National Center for Atmospheric Research. “We also want to know how and why the eye-like structure and associated intense area of low pressure developed, especially given the exceedingly rare nature of these features.”

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