Imagine a severe thunderstorm characterized by sustained winds averaging 58 miles or more per hour that gain more strength as the storm proceeds. Now imagine, this storm proceeding straight ahead and assuming the shape of an archer’s bow when looked at via radar. As odd as this type of storm may sound, it really does occur and when this weather phenomenon occurs it is known as a Derecho.
Derechos are not very common weather phenomenons, they typically tend to occur in the summer warm months, most commonly in the Nothern Hemisphere. The origin of the name Derecho derives from the Spanish word for ”straight” and was coined by Dr Gustavus Hinrichs, effectively depicting the action of these wind storms.
Derechos are often encountered during the months of July in areas such as the Ohio Valley, Upper Missisipi Valley and the Great Lakes region. In order for a Derecho to form, special circumstances need to be met. Usually, a Derecho will form on a very hot and humid day.
There are several types of Derechos that may develop and form as follows:
Serial Derechos: this occurrence took place on March 13th 1993 affecting Florida, Cuba and several regions encompassing the Gulf of Mexico, the Caribbean and the Atlantic Ocean. A serial Derecho is characterized by multiple bow echoes(crescent shaped storms) sweeping across large areas.
Progressive Derechos: this takes place when the Derecho is shaped like a single bow echo but it gradually progresses growing both in scale and strength, often reaching 250 miles in width.
Hybrid Derechos have both characteristics of serial and progressive.
Derechos are generally severe in nature. Some have been known to be characterized by winds in excess of 100 miles per hour. In 1977, a Derecho occurring in Wisconsin was known to reach winds of 115 miles per hour, while a 1998 Derecho flowing over Michigan and Wisconsin had wind gusts of 128 miles per hour. Typically, the winds found along Derechos are not constant in nature. They tend to vary considerably and are known as down bursts.
Such winds can be very damaging, bringing along trees, power poles, and over turning SUV’s, tents, mobile homes and boats. In some cases, tornadoes may develop alongside Derechos. This occurs with serial Derechos characterized by strong low pressure systems resulting in isolated super cells.
Derechos may not be quite common weather occurrences, however, in these past years of unpredictable weather and severe storms, it is worth learning about them, as it appears there has been an increase of this weather phenomenon in the recent past decades.