Two types of derecho may be distinguished based largely on the organization and behavior of the associated derecho-producing convective system. The type of derecho most often encountered during the spring and fall is a serial derecho. The second type is a progressive derecho, associated with a relatively short line of thunderstorms.
Derechos are widespread, long-lived windstorms associated with a band of rapidly moving showers or thunderstorms. Coined by Dr. Gustavus Hinrichs in 1888, "derechos", a Spanish word which means "direct" or "straight ahead".
Although a derecho's strength can produce destruction similar to tornadoes, the damage pattern produced by these events will occur along relatively straight lines. Thus the term, straight-line wind damage.
Derechos are produced by a family of downbursts clusters. Downburst clusters have overall lengths of 50 to 60 miles (80 to 100 kilometers).
A downburst cluster itself is made up of several downbursts. A downburst is an area of strong, often damaging wind produced by a convective downdraft with the overall size of the downburst varying from 4 to 6 miles (8 to 10 kilometers).
Within the downbursts are microbursts; smaller pockets of more intense wind.
While not shown in the illustration at right, within the microbursts are even smaller pockets of extreme wind called burst swaths. Burst swaths can range from 50 to 150 yards (45 to 140 meters) long. The damage pattern from burst swaths can often resemble a path of a tornado.
Due to this nature of the derecho, damage produced by these wind storms is highly variable along its path. Damage surveys following derecho events have shown that within large areas of overall damage are much smaller pockets of intense damage.
It is not uncommon for one house to be nearly destroyed while adjacent houses have relatively minor damage.
Derechos are produced by long-lived thunderstorm complexes that produce bow echoes.
- Also, see: About Derechos.