A derecho is a large cluster of thunderstorms that typically forms in late spring and summer, causing widespread destruction to trees, power lines, and sometimes structures. The term derives from the Spanish word for “straight,” as these windstorms leave long, wide areas of straight-line wind damage with speeds reaching up to 60 to 100 mph or higher in extreme cases. Meteorologists identify derechos on radar as one or more curved lines of thunderstorms called a bow echo.
The damage caused by derechos is extensive. While a single severe thunderstorm may produce only a narrow area of damaging winds, derechos can create damage that spans tens of miles wide and hundreds of miles long. For an event to be classified as a derecho, the thunderstorm-generated high winds and wind damage must cover a distance of at least 400 miles long and be at least 60 miles wide, according to a 2016 proposal led by Stephen Corfidi.
Cleanup and recovery efforts following a derecho can take days or weeks, and in severe cases, relief workers from other states may be required due to the scale of damage and power outages. The August 10, 2020, derecho in the Midwest resulted in an estimated $12.8 billion in damages across parts of eight states, leaving nearly 2 million homes and businesses without power for weeks.
Derechos are most prevalent in the U.S. during late spring and summer, with over four derechos occurring on average in both May and July. They are a particular threat in regions of the Great Plains and Midwest, with the upper Mississippi Valley through the Ohio Valley being identified as a corridor most susceptible to derechos from May to August.
These storms can be life-threatening, as evidenced by the 2016 study by Walker Ashley and Thomas Mote, which reported 153 fatalities due to derechos over an 18-year period. States such as New York, Michigan, and Ohio accounted for over a third of all derecho-related deaths.
To prepare for severe weather events like derechos, it is essential to plan ahead and stay informed. Identify safe shelter locations in advance and have a plan in place in case a National Weather Service warning is issued, especially if you live in a mobile or manufactured home.
Ensure you are prepared to quickly access shelter in the event of a derecho’s powerful winds causing damage to mobile homes. Make sure you have various methods to receive National Weather Service (NWS) warnings, such as through your smartphone or NOAA weather radio. These tools can also alert you during sleep if a warning is issued. Keep your devices fully charged before any storms approach. Move to a safe location promptly upon the issuance of warnings, whether for severe thunderstorms or tornadoes.
