Derecho danger: The fast-moving storm system that can rival hurricanes
Often mistaken for a typical thunderstorm, derechos are rare but powerful systems that unleash straight-line winds, flooding rain, and damage across hundreds of miles in just hours.
This video captured the moment a derecho arrived in State College Tuesday evening.
A derecho isn’t your average thunderstorm. While it may look like a cluster of severe storms, what sets it apart is its sheer size, speed, and destructive reach.
The term “derecho” comes from the Spanish word for “straight,” a nod to the powerful, straight-line winds that define this phenomenon. In contrast, “tornado” comes from the Spanish word meaning “to turn,” highlighting the key difference in wind behavior.
Derechos are often called “inland hurricanes” for good reason — they unleash hurricane-force winds, torrential rain, and widespread destruction. However, the two types of extreme weather form in very different ways. While a derecho may look like an inland hurricane on radar and satellite images, and seem like the same in person with its combination of strong winds and torrential rain, the meteorological community has criteria that determine whether or not a thunderstorm complex has achieved the "d-word" level.
Historically, the definition dictated that severe, damaging, straight-line winds occurred along a continuous 240-mile-long path or greater. However, in 2021 the Storm Prediction Center (SPC) updated its definition to "400 miles (about 650 km) with a width of at least 60 miles (about 100 km)." A derecho must include wind gusts of at least 58 mph or greater along most of its path, with isolated gusts of at least 75 mph.
A deadly derecho tore across multiple states on April 29, knocking down power poles, stripping the siding off of buildings and ripping apart trees.
Most derecho damage comes from intense downbursts — winds that push outward and knock down trees, power lines, and structures in a straight path. These violent systems can also bring very large hail, flash flooding, and isolated tornadoes, making them one of the most destructive — and underestimated — severe weather threats in the central and eastern U.S.
Due to the widespread, intense winds, people should prepare for an approaching derecho the same way they would if a tornado were approaching.
A line of severe thunderstorms evolved into a derecho on April 29, bringing destructive wind gusts across parts of the Ohio Valley and interior Northeast. At least three people died and 700,000 were left in the dark due to widespread power outages, the majority of which occurred in Pennsylvania.
This radar looop shows the derecho moving across Indiana, Ohio, Pennsylvania and New York. At least 3 deaths have been reported in Pennsylvania related to the violent storm.
Local storms reports as of April 29, 2025 11 p.m. EDT via the Storm Prediction Center.
Wind gusts between 65 mph and 80 mph were clocked in eastern Ohio and western Pennsylvania as the derecho raced through the region. Winds in Latrobe, Pennsylvania, reached 79 mph, one of the highest gusts reported on Tuesday evening.
Pittsburgh airport measured a wind gust of 71 mph, the third-highest wind gust ever measured at the airport, only behind 75 mph winds measured on April 8, 2020, and an 83-mph gust reported on July 10, 1992.
Other examples of famous, deadly and damaging derechos include the long-lived thunderstorm complex during the summer of 2012 known as the "D.C. Derecho."
High wind and wind damage reports from the "DC Derecho" on June 29, 2012.
The 2012 derecho roared to life over Iowa on June 29 and tore across nearly 800 miles in just two days, reaching the Mid-Atlantic coast by June 30.
Along its path, the storm left a trail of devastation: nearly two dozen lives lost, more than $3 billion in damage, and over 4 million homes and businesses plunged into darkness. Trees snapped like matchsticks, power lines crumpled under the force of the wind, and entire communities were left scrambling to recover in the sweltering summer heat.
In this June 30, 2012, photo, an American Beech tree is down on Capitol Hill grounds in Washington, D.C., across from the U.S. Supreme Court after a derecho swept across the region. (AP/Manuel Balce Ceneta)
Dozens of derechos have been documented over the past four decades, but few stand out like the series that struck between July 11–15, 1995, when four separate derechos tore across the northern U.S. in just five days. The damage from those events neared $1 billion.
"Derechos and their parent thunderstorm complexes often form and move along the northern edge of a large rim of heat," AccuWeather Senior Meteorologist Dan Pydynowski said. This region often aligns with a strong upper-level jet stream, which supercharges the storms and propels them forward at remarkable speeds. There are exceptions, however, like the one that hit the Northeast on April 29, 2025.
AccuWeather’s Bernie Rayno explains what a derecho is.
While clusters of thunderstorms are a regular feature of late spring and summer, only a small fraction reach the intensity, scale, and longevity required to be classified as a derecho.
And these powerful storms aren’t limited to North America. Derechos have also been observed in parts of Europe in recent decades.
As a derecho passes, temperatures may hold steady, surge with building heat, or drop as cooler air moves in -- adding to the danger. Some towns can be left without power for days, meaning people may be left without air conditioning if one is followed by a heat wave.
It’s important not to confuse derechos with squall lines — both are lines of thunderstorms, but they behave differently. A squall line typically forms along or just ahead of a cold front and marks the boundary between air masses. Some squall lines stretch more than 1,000 miles and can travel similar distances in extreme cases. But while squall lines may weaken quickly or bring scattered severe weather, derechos tend to sustain their intensity and deliver widespread, long-track wind damage.
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