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DERECHO FACTS PAGE... Note: Some of the following information, in abbreviated, question-and-answer format, is available in The Derecho FAQ. INTRODUCTION Definition of a derecho A derecho (pronounced similar to "deh-REY-cho" in English, or pronounced phonetically as " ") is a widespread, Wind Damage To Plants long-lived wind storm. 

Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems. Although a derecho can produce destruction similar to that of a tornado, Wind Damage To Plants the damage typically occurs in one direction along a relatively straight path. 

As a result, the term "straight-line wind damage" sometimes is used to describe derecho damage. By definition, if the swath of wind damage extends for more than 240 miles (about 400 kilometers), includes wind gusts of at least 58 mph (93 km/h) along most of its length, and several, well-separated 75 mph (121 km/h) or greater gusts, then the event may be classified as a derecho. 

Origin of the term "derecho" The word "derecho" was coined by Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, Wind Damage To Plants in a paper published in the American Meteorological Journal in 1888. A defining excerpt from the paper can be seen in this figure showing a derecho crossing Iowa on July 31, 1877. 

Hinrichs used the word "derecho" to distinguish thunderstorm-induced Wind Damage To Plants straight-line winds from the damaging rotary winds produced by tornadoes. 

While the term was adopted to a limited extent by the meteorological community during the late nineteenth century, "derecho" disappeared from use for nearly a century until being resurrected by severe weather Wind Damage To Plants meteorologists in the mid-1980s. "Derecho" is a Spanish word meaning "direct" or "straight ahead." 

In contrast, the word "tornado" is thought by some, including Hinrichs, to have been derived from the Spanish word "tornar," which means "to turn." Because "derecho" is of Spanish origin, Wind Damage To Plants the plural form is spelled "derechos;" i.e., the letter "e" is not added after the letter "o." 

A web page about Gustavus Hinrichs has been created by Ray Wolf of the Davenport, Iowa National Weather Service Forecast Office. The page Wind Damage To Plants provides information on Hinrichs' background, and on his development of the term "derecho" in the late 1800s. Wolf's page also briefly discusses how the term "derecho" has come into more common use in recent years. 

STRENGTH AND VARIATION OF DERECHO WINDS Strength of derecho winds By definition, Wind Damage To Plants winds in a derecho must meet the National Weather Service criterion for severe wind gusts (greater than 57 mph) at most points along the derecho path. But in stronger derechos, winds may exceed 100 mph. 

For example, as a derecho roared through northern Wisconsin on July 4, 1977, winds of 115 mph were measured. More recently, Wind Damage To Plants the derecho that swept across Wisconsin and Lower Michigan during the early morning of May 31, 1998 produced a measured wind gust of 128 mph in eastern Wisconsin, and estimated gusts up to 130 mph in Lower Michigan. 

Variation of wind speeds in a derecho The winds associated with derechos are not constant and may vary considerably along the derecho path, Wind Damage To Plants sometimes being below severe limits (57 mph or less), and sometimes being very strong (from 75 mph to greater than 100 mph). 

This is because the swaths of stronger winds within the general path of a derecho are produced by what are called downbursts, and downbursts often occur in irregularly-arranged clusters, Wind Damage To Plants along with embedded microbursts and burst swaths. 

Derechos might be said to be made up of families of downburst clusters that extend, by definition, continuously or nearly continuously for at least 240 miles (about 400 km). The derecho of July 4-5, 1980 is a good example of an event that exhibited wide variation in observed wind speeds due to embedded microbursts, downbursts, and Wind Damage To Plants downburst clusters. 

More on microbursts, downbursts, and downburst clusters may be found in Derecho-producing storms. CASUALTY AND DAMAGE RISKS Those most at risk from derechos Because derechos are most common in the warm season, Wind Damage To Plants those involved in outdoor activities are most at risk. 

Campers or hikers in forested areas are vulnerable to being injured or killed by falling trees. People at sea risk injury or drowning from storm winds and Wind Damage To Plants high waves that can overturn boats. Occupants of cars and trucks also are vulnerable to being hit by falling trees and utility poles. 

Further, high profile vehicles such as semi-trailer trucks, buses, and sport utility vehicles may be blown over. At outside events such as fairs and Wind Damage To Plants festivals, people may be killed or injured by collapsing tents and flying debris. Even those indoors may be at risk for death or injury during derechos. 

Mobile homes, in particular, may be overturned or destroyed, while barns and similar buildings can collapse. People inside homes, businesses, and Wind Damage To Plants schools are sometimes victims of falling trees and branches that crash through walls and roofs; they also may be injured by flying glass from broken windows. 

Finally, structural damage to the building itself (for example, removal of a roof) could pose danger to those within. Another reason that those outdoors are especially vulnerable to derechos is the rapid movement of the parent convective system. Typically, Wind Damage To Plants derecho-producing storm systems move at speeds of 50 mph or greater, and a few have been clocked at 70 mph. 

For someone caught outside, such rapid movement means that darkening skies and other visual cues that serve to alert one to the impending danger (e.g., gust front shelf clouds --- see photo at top of page) appear on very short notice. In summary, Wind Damage To Plants the advance notice given by a derecho often is not sufficient for one to take protective action. 

The following links provide personal stories of those who have survived derechos while outdoors: - A camper's close brush with death during the July 4-5, 1999 derecho in Maine. - A boater's encounter with the May 17, 1986 derecho on Lake Livingston, Texas. - A dramatic account of a Wind Damage To Plants boat overturned by intense straight-line winds during a July 1943 wind storm near Goshen, Indiana. 

For a more comprehensive view of derecho hazards, the "Noteworthy Event" page for the July 4-5, 1980 derecho lists the cause of death or injury for the 73 casualties of that event, Wind Damage To Plants providing a typical example of the risks to humans posed by derechos.

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