Derecho
A derecho is a significant and destructive windstorm characterized by a long path of straight-line winds, typically associated with thunderstorm systems such as squall lines or bow echoes. The term "derecho," derived from Spanish meaning "direct" or "straight ahead," describes the nature of the damage, which usually moves in a consistent direction, unlike the more chaotic destruction from tornadoes. To qualify as a derecho, a storm must produce wind gusts of at least 58 mph over a distance exceeding 250 miles, often leading to extensive damage and power outages.
Derechos are most common in the United States during late spring and summer months, particularly from May to July. They can arise from intense heat waves, where moisture-laden air interacts with cooler air to create conditions conducive to severe thunderstorms. The damage caused by derechos can be severe, with historical events resulting in fatalities and widespread destruction, exemplified by the devastating storm in June 2012.
Meteorologists have made strides in understanding and documenting derechos, leading to improved detection methods, although nighttime events are particularly hazardous due to reduced visibility and awareness among those in affected areas.
On this Page
Subject Terms
Derecho
A derecho is a widespread, lengthy windstorm associated with bands of rapidly moving showers or thunderstorms commonly referred to as bow echoes, squall lines, or quasi-linear convective systems. In English, the word is pronounced "deh-REY-cho."
The term derecho is a Spanish word meaning direct or straight ahead; the word tornado is derived from the Spanish word tornar, which means to turn.
Although both derechos and tornados produce destructive results, the damage caused by a derecho appears mostly in one direction along a relatively straight path. As a result, the term "straight-line wind damage" often describes the destruction that a derecho brings.
Derecho damage is usually easily discernible from tornadic damage, as most trees and other wreckage fall in the same direction as a result of powerful wind speeds. This is the opposite of what takes place in a tornado, when debris is typically twisted, or shredded, and swept in all directions.
Brief History
The word derecho was coined in 1888 by Dr. Gustavus Hinrichs, a professor of physics at the University of Iowa. In the 1880s, the meteorological community adopted the term to some extent, but it was then forgotten for nearly a century.
A 1987 paper by meteorologists Johns and Hirt reintroduced the term derecho to the meteorological community. It stated that to be defined as a derecho, a thunderstorm’s outflow winds must reach 75 mph or greater at several points along the damage path.
In 2004, Coniglio and Stensrud plotted a grid of derechos occurring across the continental United States in order to determine the number of times each grid square was at least partly affected by a derecho event during the period of 1980-2001. The results of the grid created a climatology of derecho occurrence in the United States and helped to establish the existence of "moderate and high intensity" derechos in the United States.
Many papers have been presented on the various aspects of derechos, and much of the material is based on actual derechos that have been documented since 2005.
The first major derecho to be recorded was in 1994 and moved through Utah and Wyoming. In 2010, a major storm hit the Chicago area with wind reports of over 70 mph. A couple of tornadoes touched down, and hail as large as tennis balls fell from the sky.
The most violent and deadly derecho to occur in North American history hit the mid-Atlantic and Midwestern states in June 2012, starting in the afternoon and evening of June 29 and lasting through the early morning hours of June 30. It started as a small thunderstorm cell in central Iowa, continued into Illinois, and progressed across a large section of the Midwest and central Appalachians into the Mid-Atlantic States, including Ohio, New Jersey, Pennsylvania, Virginia, West Virginia, and Washington, DC.
The damage was extensive, and millions of power outages across the entire area lasted for almost a week. Between twenty-two and twenty-four lives were lost during the storm.
Derecho Today
Derechos have been defined over the years as storms that leave a swath of wind damage that extends for more than 250 miles (about 400 kilometers). It includes wind gusts of at least 58 mph (93 km/h) along most of its length, as well as several, well-separated 75 mph (121 km/h) or greater gusts. They are sometimes referred to as inland hurricanes due to the hurricane-like conditions, in terms of their ferocious winds and torrential rains. In comparison, an ordinary thunderstorm produces a band of damaging winds, usually only a mile or two wide and a few miles long.
In 2016, meteorologists considered updating the term to make it more focused on the meteorological processes they believe create its organized, destructive surface winds, and including the presence of certain radar-observed structural features such as rear-inflow jets and bow echoes. Some meteorologists have suggested increasing the length of the wind requirement to 650 km (400 miles), and dropping the requirement for specific observed wind gusts altogether.
A derecho usually begins with an intense heat wave across much of the central and eastern part of the United States. Moist, hot air follows a high pressure center and flows through the Ohio Valley and into the Mid-Atlantic region. When a stationary front is set up between the heat wave and (slightly) cooler air to the north, it creates a pool of moisture in the area of the stationary front. This sets up the necessary conditions to feed thunderstorm development.
Once these conditions are met, the cold pool may start to move away from the storm, and by tilting up toward the updraft, it allows the storm to start to move along the surface while also gaining in strength. This is the beginning of a derecho.
Derechos are widespread and can cause a great deal of damage over a broad area, as opposed to tornadoes that are more defined and travel over a smaller strip of land. They often last well through the night, and although meteorologists have tools to detect storms, including tornadoes and derechos, people are usually unable to detect severe weather coming at night. They might sleep through the warnings, not hear the storm coming, or not see the accompanying flashes of lightning until the last minute, so they often find themselves caught up in the storm and unable to save themselves from injury or death.
Derechos occur most frequently in the United States during the late spring and summer, peaking in May, June, and July.
According to the report, close to 70 percent of derecho fatalities occurred in areas outside permanent buildings. Thirty percent of victims were in vehicles, 90 percent were in boats, 11 percent were under trees, and 9 percent were camping.
Bibliography
"About Derechos." NOAA-NWS-NCEP Storm Prediction Center website, n.d. Web. 18 June 2016.
Coniglio, Michael C., David J. Stensrud, and Michael B. Richman. "An Observational Study Of Derecho-Producing Convective Systems." Weather and. Forecasting 19.2 (2004): 320-37.
Dolce, Chris, and Jonathan Erdman. "Derecho: The Science Behind Widespread Damaging Thunderstorm Winds." The Weather Channel, 21 June 2015. Web. 19 June 2016.
Haby, Jeff. "What Is a Derecho?" The Weather Prediction, n.d. Web. 19 June 2016.
Johns, Robert H., and William D. Hirt. "Derechos: Widespread Convectively Induced Windstorms." Weather Forecasting 2.1 (1987): 32-49.
Mersereau, Dennis. "What Is a Derecho?" The Vane, 4 Aug. 2014. Web. 19 June 2016.
"More on the Climatology of Derechos in the United States." SPC.NOAA: Climatology Page, n.d. Web. 19 June 2016.
Murphy, M. "Derechos: The Facts." Weather Works. Your Weather Experts. Weather Works, Your Weather Experts, LLC, 2012. Web. 19 June 2016.
Mussoline, Meghan. "What Is a Derecho?" Accuweather.com, 14 July 2015. Web. 19 June 2016.
Oskin, Becky. "Derecho Facts, Formation and Forecasting." Live Science, 7 Jan. 2015. Web. 19 June 2016.
Tucker, Emma. "What Is a Derecho and Why Is It So Destructive?" CNN, 14 July 2023, www.cnn.com/2023/02/27/weather/derecho-damaging-wind-event-xpn/index.html. Accessed 16 Nov. 2024.