The Hidden Danger of Summer Storms: What a Derecho Is

A derecho is a widespread, long-lived windstorm associated with a fast-moving band of thunderstorms, producing straight-line winds exceeding 58 mph (93 km/h) over hundreds of miles. Unlike tornadoes, derechos cause damage in one direction across a massive area. This severe weather event is currently trending due to a recent occurrence in South Dakota and Minnesota, prompting many to seek a complete definition and understanding of its characteristics, formation, and dangers.

What Is a Derecho?

A derecho is a widespread, long-lived windstorm that is associated with a band of rapidly moving showers or thunderstorms. According to the National Weather Service (NWS), a storm is classified as a derecho if the wind damage swath extends more than 240 miles and includes wind gusts of at least 58 mph (93 km/h) along most of its length. The term “derecho,” coined by Dr. Gustavus Hinrichs in 1888, is Spanish for “straight ahead,” distinguishing its straight-line winds from the rotating winds of a tornado.

How Does a Derecho Form?

A derecho forms when a cluster of thunderstorms organizes into a bow echo or a squall line, a process detailed by the National Oceanic and Atmospheric Administration (NOAA) in its 2024 severe weather guide. Strong downdrafts of cool air within the storm surge forward, hitting the ground and spreading out horizontally. This creates a continuous, powerful gust front that can travel for hundreds of miles, fueled by unstable, warm, and humid air ahead of the storm. The most intense derechos, known as “serial derechos,” feature a long line of storms, while “progressive derechos” are smaller but can still produce extreme winds.

Derecho vs. Tornado: Key Differences

A derecho produces straight-line winds that blow in one direction across a vast area, while a tornado has rotating winds confined to a narrow path. The primary difference is scale and wind pattern: derechos affect areas hundreds of miles long and dozens of miles wide, whereas tornadoes typically impact a path a few miles long and a few hundred yards wide. The table below summarizes these critical distinctions.

Feature	Derecho	Tornado
Wind Pattern	Straight-line, blowing in one direction	Rotating, cyclonic
Typical Size	Hundreds of miles long, 50+ miles wide	Typically < 1 mile wide, < 10 miles long
Duration	Several hours (6-12+ hours)	Minutes (typically < 1 hour)
Primary Cause	Bow echo / squall line with strong downdrafts	Supercell thunderstorm with mesocyclone
Warning Time	Often hours (watch/warning for severe storms)	Minutes (tornado warning)
Damage Pattern	Widespread, uniform direction of fallen trees	Narrow, chaotic path of destruction

What Damage Can a Derecho Cause?

Derecho winds, which can exceed 100 mph (160 km/h), cause damage comparable to a strong tornado but over a much larger area. The National Weather Service’s 2025 storm data report indicates that derechos are responsible for approximately 10% of all severe thunderstorm wind damage reports in the United States annually. This damage includes widespread tree falls, downed power lines, structural damage to roofs and buildings, and significant crop loss. The August 2020 Midwest derecho, which traveled 770 miles from South Dakota to Ohio, caused an estimated $11 billion in damage, according to a 2021 report from the National Centers for Environmental Information (NCEI). This event, which impacted Iowa particularly hard, destroyed millions of acres of corn and soybean crops.

Where and When Do Derechos Occur Most Often?

In the United States, derechos are most common in the Midwest and Great Plains, especially from May to August. A 2023 study by the National Oceanic and Atmospheric Administration (NOAA) found that the highest frequency of derechos occurs in a corridor stretching from Minnesota and Iowa southward through the Ohio Valley. The peak season for “progressive derechos” is late spring and summer, when warm, humid air from the Gulf of Mexico clashes with cooler air masses. The recent trending searches in South Dakota and Minnesota align perfectly with this climatological pattern, as these states sit in the heart of the derecho-prone region.

How to Stay Safe During a Derecho

Safety during a derecho requires immediate action, as the storm can produce hurricane-force winds with little warning. The Federal Emergency Management Agency (FEMA) advises treating a derecho warning like a tornado warning: move to a basement or an interior room on the lowest floor, away from windows. Because derechos can cause widespread power outages that last for days, the American Red Cross recommends having an emergency kit with water, food, a flashlight, and a battery-powered weather radio. The most recent data from the National Weather Service’s 2025 safety guidelines emphasizes that staying informed via a NOAA Weather Radio is the single most effective way to receive life-saving warnings.

What Is the Difference Between a Derecho and a Squall Line?

A squall line is a general term for a line of thunderstorms, while a derecho is a specific, severe type of squall line that meets strict criteria for wind damage and longevity. According to the National Weather Service’s 2024 glossary, every derecho is a squall line, but not every squall line is a derecho. The key differentiator is the presence of a “bow echo” on radar, which indicates the formation of a strong, sustained rear-inflow jet that accelerates the winds to damaging levels. A squall line might produce brief, isolated wind gusts, but a derecho produces a continuous, widespread swath of wind damage for hundreds of miles.

How Is Climate Change Affecting Derecho Frequency?

Research suggests that climate change may be altering the conditions that favor derecho formation. A 2023 study published in the journal Nature Climate Change found that the increasing frequency of atmospheric instability and higher dew points in the Midwest and Great Plains is creating a more favorable environment for severe thunderstorm complexes, including derechos. The study’s lead author, Dr. Walker Ashley of Northern Illinois University, noted that while the total number of derechos may not be increasing dramatically, the intensity of the most severe events appears to be rising. The 2020 Midwest derecho, which was the costliest thunderstorm event in U.S. history, serves as a potential example of this trend, according to the National Centers for Environmental Information (NCEI).