Derecho, << day RAY choh, >> is a widespread, long-lived windstorm associated with a line of thunderstorms. A derecho can sometimes last for more than a day and blow across several hundred miles. However, its strong winds typically blow for less than 10 minutes at any particular location in its path. A derecho’s winds often blow between 58 and 75 miles (95 and 120 kilometers) per hour, although gusts can occasionally exceed 120 miles (195 kilometers) per hour. A derecho’s wind speeds are typically less than those of a tornado. But a derecho can still cause damage to buildings, widespread power outages, injuries, and even deaths.
A derecho does not cause damage in a spiral or circular pattern, as do many tornadoes. Instead, derecho damage occurs in straight lines. For example, fallen objects such as trees and power lines point in the same direction after a derecho has passed. On occasion, derecho winds and tornadoes may occur within the same line of thunderstorms.
In the United States, derechos almost always occur east of the Rocky Mountains. They usually develop in the spring and summer. But they may occur at any time of the year.
When viewed on a weather radar, the line of thunderstorms that produces a derecho is normally bowed (curved). Such a pattern is called a bow echo. A derecho-producing storm can include from one to several bow echoes.
Derechos are classified into three categories: (1) serial, (2) progressive, and (3) hybrid. Serial derechos may be hundreds of miles or kilometers across and contain many bow echoes. Progressive derechos are narrow compared with serial derechos. Progressive derechos are between 40 and 250 miles (65 and 400 kilometers) across. They may contain only one bow echo. Hybrid derechos have a mix of characteristics of both serial and progressive derechos.
Derechos often form near a weather front that separates a warm and humid air mass from a cooler and drier one. Weather fronts are borders between two or more air masses with different characteristics. Most U.S. derechos gain their strength from the warm and humid air that flows north from the Gulf of Mexico. In general, warm air contains more energy than cool air.
Derecho is Spanish for straight ahead. The term refers to the straight-forward motion of the derecho’s powerful winds. The Danish-born American scientist Gustavus D. Hinrichs established the term in a paper published in 1888.
