A derecho is a large, fast-moving complex of thunderstorms distinguished by straight-line winds, intense rain, and destruction that can span hundreds of miles in just a few hours. Though they might appear similar to regular thunderstorm clusters, derechos are defined by their scale, speed, and power.
The term originates from the Spanish word for “straight,” referencing the nature of their winds, unlike tornadoes, which derive their name from the Spanish word meaning “to turn.” This difference in wind behavior is a fundamental distinction between the two.
Defining Characteristics
In 2021, the Storm Prediction Center (SPC) updated the criteria for classifying a derecho:
- Must produce damaging, straight-line winds along a path at least 400 miles long and 60 miles wide
- Must include wind gusts of 58 mph or greater along most of its path
- Isolated gusts should reach at least 75 mph
These storms are often dubbed “inland hurricanes” because of their intense wind speeds and torrential rain, although their formation differs significantly from tropical systems.
The Danger of Derechos
Most of the damage caused by derechos stems from downbursts — powerful winds that blow outward from the storm, knocking over trees, power lines, and even structures in a straight path. Derechos can also bring:
- Large hail
- Flash flooding
- Isolated tornadoes
Due to their severity, it’s advised to prepare for a derecho in the same way one would prepare for a tornado.
April 29, 2025 Derecho Event
A recent derecho on April 29, 2025, caused widespread damage as it traveled through parts of Indiana, Ohio, Pennsylvania, and New York:
- Wind gusts:
- Latrobe, PA: 79 mph
- Pittsburgh Airport: 71 mph (third-highest on record at that location)
- Casualties: At least three deaths reported in Pennsylvania
- Power outages: Over 700,000 people left without electricity
This storm left a significant trail of destruction, especially in eastern Ohio and western Pennsylvania.
Historical derechos
June 29–30, 2012 – The “D.C. Derecho”
- Originated in Iowa and traveled nearly 800 miles to the Mid-Atlantic
- Resulted in approximately 20 fatalities, $3 billion in damage, and over 4 million power outages
- Captured national attention for its scope and ferocity
July 11–15, 1995
- Four separate derechos struck the northern U.S. within five days
- Caused nearly $1 billion in damages
How Derechos Form
According to AccuWeather Senior Meteorologist Dan Pydynowski, derechos often develop along the northern edge of a large heat dome, powered by a strong upper-level jet stream. This enhances storm strength and speed. However, not all derechos follow this pattern — as evidenced by the April 2025 event in the Northeast.
Derechos vs. Squall Lines
Although both involve thunderstorm lines, they are not the same:
- Squall lines:
- Typically form along cold fronts
- Can span over 1,000 miles
- May dissipate quickly or cause scattered severe weather
- Derechos:
- Sustain long-track wind damage
- Maintain high intensity over long distances
Global presence and aftermath
Though most common in North America, derechos have also been recorded in Europe. As these systems pass, temperatures can fluctuate — remaining steady, increasing due to heat, or dropping as cooler air arrives. In the aftermath, some areas may face extended power outages, heightening risks during subsequent heat waves.
Based on information from AccuWeather (Updated April 30, 2025, by Monica Danielle)
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