Derechos, though less well-known than hurricanes or tornadoes, are rare but highly destructive storms. Commonly occurring in late spring and summer across the central and eastern United States, these storms generate intense straight-line winds that can span hundreds of miles, causing widespread damage.
On August 10, 2020, a powerful derecho impacted the Midwest, traveling 770 miles in 14 hours and leaving over a million people without power.The term “derecho,” meaning “straight ahead” in Spanish, was first coined by Gustavus Hinrichs in 1888.
A derecho is defined as a long-lived windstorm associated with a line of thunderstorms, with winds exceeding 58 mph. The 2020 event saw winds reaching 112 mph, underscoring the immense force of these storms.
Read More: What is a Derecho and What Makes It So Destructive?
How Derechos Form
Normal thunderstorms develop when warm air rises from the Earth’s surface into the cooler upper atmosphere. As the warm air ascends, it cools and reaches its dew point—the temperature at which water vapor condenses into liquid droplets, forming clouds.
This cooled air then descends back toward the Earth’s surface, where it warms once more, initiating the cycle again. This continual process of convection ultimately leads to the development of a thunderstorm.
A critical element in the formation of derechos is the storm’s downdraft—the downward movement of cool air. When this cooler air strikes the ground, it spreads outward, pushing warm surface air into an area of gusty winds.
These downdrafts, which can extend up to six miles across, create intense wind currents, drawing more air into the storm, which in turn strengthens it.When a cluster of strong downdraft winds in the core of a storm accelerates ahead of the system, it forms a phenomenon known as a bow echo.
This distinctive bending of the storm’s front forces even more warm air into the atmosphere, intensifying the storm’s power. When this bow echo, or a series of them, spans distances greater than 250 miles and generates wind gusts exceeding 58 miles per hour, the event is officially classified as a derecho.
Where Derechos Occur
Derechos are a global phenomenon, though they are most prevalent in the central and eastern United States. On average, these storms occur one to two times annually in this region, compared to over a thousand tornadoes that strike the country each year.
Derechos typically form during the late spring and summer months when high-pressure systems—large masses of descending air—move northward from the tropics into the U.S. However, some derechos can also occur in cooler weather, primarily in the region stretching from Texas to the Southeast.
In May 2009, a powerful “Super Derecho” produced wind gusts reaching 106 miles per hour as it moved from Kansas to eastern Kentucky. Although the storm was initially described as an inland hurricane, it was ultimately classified as a derecho, albeit with several tornadoes embedded within its winds.
Beyond the United States, derechos have been observed in other parts of the world, including Eastern Europe and South Asia. In 2002, a devastating derecho struck eastern Germany, killing eight people and injuring 39, with Berlin suffering the most significant damage.
Derecho Damage
While derechos can be as destructive as tornadoes, they cause damage in a distinct way. The chaotic, rotating winds of a tornado scatter debris in all directions, while a derecho’s straight-line winds, though similar to those of a typical thunderstorm, are much stronger.
For example, on August 10, 2020, a derecho in Wheaton, Illinois, toppled the steeple at College Church and caused extensive tree damage in a nearby park.
Downburst clusters, which are common in derechos, can stretch four to six miles in length and contain smaller, more intense wind pockets known as microbursts and burst swaths.
These areas of concentrated, high-speed winds—up to 100 miles per hour—can cause tornado-like damage within a relatively small, localized area.
After a derecho, it’s not uncommon to see vast destruction in some places, while nearby areas remain largely unaffected.Derechos are also notorious for causing long-lasting power outages.
For example, the June 2012 derecho knocked out electricity for more than five million people from Chicago to the mid-Atlantic.
These rapidly moving storms pose a particular risk to anyone caught outdoors, such as campers or hikers, as they can develop with little warning, providing only hours or even minutes to seek shelter.
Thunderstorms can quickly evolve into derechos, underscoring the importance of taking storm warnings seriously.
Frequently Asked Questions (FAQs)
What is a derecho?
A derecho is a widespread, long-lasting windstorm associated with a fast-moving group of severe thunderstorms. It is characterized by straight-line winds that can cause damage similar to that of a tornado, but over a much broader area. These winds can exceed 58 miles per hour and may cause destruction to trees, buildings, power lines, and vehicles.
How do derechos form?
Derechos typically form when warm, moist air rises and cools within a thunderstorm, causing a downdraft. When the cool air reaches the ground, it spreads out, pushing warm air upward and creating strong winds. When these winds accelerate and form a “bow echo,” they intensify the storm, and when sustained over 250 miles with wind gusts greater than 58 mph, it is classified as a derecho.
Where do derechos occur?
While derechos can occur around the world, they are most common in the central and eastern United States, especially during the late spring and summer months. They have also been observed in parts of Eastern Europe and South Asia.
How often do derechos occur?
In the United States, derechos occur, on average, one to two times per year. Although less frequent than tornadoes, derechos can be just as destructive, if not more so, because they affect much larger areas.
What is the difference between a tornado and a derecho?
The main difference lies in the type of winds they produce. Tornadoes involve rotating winds that cause localized damage in a small, concentrated area, whereas derechos are associated with straight-line winds that affect much larger areas. Derechos also tend to be more widespread and longer-lasting than tornadoes.
Can derechos cause tornadoes?
Yes, derechos can produce tornadoes within their wind fields. These tornadoes, however, are usually smaller and less intense than those produced by more traditional supercell thunderstorms.
Conclusion
Derechos are powerful and potentially devastating weather phenomena that can cause widespread damage, particularly through their intense, straight-line winds. While they are often less well-known than tornadoes, they can be just as destructive, affecting vast areas and leading to long-lasting power outages, downed trees, and structural damage. Understanding how derechos form, where they occur, and the risks they pose is crucial for preparedness.
