A derecho is a long-lived, fast‑moving line of thunderstorms that can stretch hundreds of miles and last eight hours or more. Gino Izzi, a meteorologist at the National Weather Service in Chicago, told the Associated Press, “There has been instances where derechos have moved from Iowa all the way to Washington, DC.”
These storms unleash straight‑line winds over 60 mph (97 km/h), causing damage that can, in some cases, be way more intense than in the aftermath of tornadoes or hurricanes.
Derechos feed on hot, moist and unstable air. Although they can form any time of year, they are most likely to occur in July and early August. Derechos are uncommon: while some years see none, others witness just a few of those extreme weather events.
Different Types of Derechos
Serial derechos form with large, powerful storm systems in spring, fall and early winter.
Progressive derechos are smaller but intense, common in summer when heat and humidity dominate.
Hybrid derechos combine traits of both.
While derechos mostly produce straight‑line wind damage, they can also entail small tornadoes. But unlike tornadoes whose damage swaths are usually under a mile, derechos can carve out paths over 100 miles wide, according to the Associated Press.
Where Do They Occur?
These storms can occur nearly anywhere in the US, but are most frequent in the central and eastern regions.
Progressive derechos typically sweep from the northern and central Plains into the Midwest, Great Lakes, and Ohio Valley.
These zones often have atmospheric instability fuelled by heat domes, strong jet stream winds, and humid “corn sweat” from growing crops.
Historic examples include:
- A 2003 derecho that crossed from Arkansas through Alabama, Georgia, and South Carolina, reportedly killing two people and injuring 11 others.
- The 2009 “Super Derecho” barrelled from Kansas to Kentucky, causing several deaths and an estimated total of over $500 million in damage, as reported by the US-based news agency.
- In 2020, a derecho was witnessed from eastern Nebraska into Iowa and parts of Wisconsin and Illinois, packing winds near 100 mph (160 km/h). Reports suggest Cedar Rapids residents woke up to find nearly 100,000 trees either snapped or uprooted.
- A December 2021 derecho was reported across the Plains and Upper Midwest, which triggered at least 45 tornadoes, reportedly killing at least five people, while leaving a trail of heavy destruction.
Derecho-Related Flooding
Though driven by wind, derechos can stall or move slowly, dumping heavy rain that can often lead to flash floods. A July 1969 derecho in Ohio caused Killbuck Creek to surge more than 20 feet above normal, resulting in at least two dozen fatalities.
ALSO READ: At Least 3 Dead, Hundreds Evacuated as Flash Floods Batter Romania
