Derecho

Definition: Derecho is a Spanish word meaning “straight” or “direct”. In terms of weather, a derecho is a long-lived windstorm with winds in excess of 58 mph. This is equivalent to the damage that can occur during an F1 tornado. The winds are sustained winds and not simply single bursts of wind. There can be gusts of winds in excess of 100 mph. The winds are non-tornadic, although an actual tornado can accompany a derecho. The storms are over 250 miles in length and can cause extensive damage.

Derechos are most common in warm temperatures with July being a peak month to experience a derecho as can be seen in this diagram of monthly derecho freuquencies. However, derechos have been observed in all months of the year.

The term derecho has been around for a long time. It was first described by Gustavus Hinrichs in 1888. The term was later revived by Robert Johns and William Hirt in 1987. Although derechos in other countries can happen, Johns and Hirt identify areas from the upper Midwest to the Ohio valley as particularly prone to these wind events. Occasionally, these storms will move into the Appalachia regions.

Dr. Ted Fujita first coined the term “bow echo” to describe the bow shaped path of mesoscale convective systems (thunderstorms). Derechos usually evolve from a bow echo formation and have become somewhat synonymous with the term “long-lived bow echo”. The storm that caused Fujita to coin the term “bow echo” had a derecho event that affected Northern Wisconsin known as the The Independence Day Derecho of 1977.

Sources:

NWS Derecho FAQ Page
On the Climatology of Derechos by Michael C. Coniglio and David J. Stensrud
Synoptic and Mesoscale Analysis of the 9 August 2000 Appalachian-Crossing Derechos by Steve Keighton and Steve Nogueira
The Structure and Evolution of Squall Line and Bow Echo Convective Systems