What is Derecho? | Weather.com
- Derechos are large-scale damaging wind events resulting from clusters of severe thunderstorms.
- They are most common in late spring and summer.
- Parts of the Great Plains and Midwest experience derechos most often.
A derecho is a large group of thunderstorms that commonly form in late spring and summer and cause widespread destruction to trees, power lines, and sometimes structures.
Here’s what this term means: From the Spanish word for “straight,” these wind gusts leave wide, long swaths of straight wind damage. Wind speeds can reach 60 to 100 mph or higher in extreme cases.
For meteorologists, they have a distinctive look on radar, usually in the form of one or more curved lines of thunderstorms known as a bow echo.
This is a radar sequence for August 10, 2020 in the Midwest region from 8 AM to 7 PM CDT.
(NWS-Chicago)
Their damage is extensive. A single severe thunderstorm may produce an area of damaging winds only a mile or two wide and perhaps a few miles long, but derechos can produce damage tens of miles wide and hundreds of miles long.
To be called a derecho, the high winds generated by thunderstorms and wind damage would have to cover a distance of at least 400 miles and be at least 60 miles wide, according to a 2016 proposal led by Stephen Corvidi.
The cleaning and recovery process can take days or weeks. In the worst derecho events, relief workers from other states are sometimes needed to assist in these efforts due to the scope of the damage and power outages.
Hurricane Derecho in the Midwest on August 10, 2020, caused an estimated $12.8 billion in damage, sweeping through parts of eight states. Nearly 2 million homes and businesses were without power. Some have not had their strength restored for weeks.
In this aerial photo taken with a drone, damaged grain bins are visible at a Heartland Co-Op grain elevator on August 11, 2020, in Luther, Iowa.
(Daniel Acker/Getty Images)
Derechos in the United States are most numerous during the late spring and summer. A 2005 study by Walker Ashley and Thomas Mott found that May and July average more than four derechos per year. June is almost always active with three to four derechos annually.
More than 75% of them occur between April and August, according to NOAA’s Storm Prediction Center.
Derechos pose a potential threat to many east of the Rocky Mountains. But they are especially threatening in parts of the Great Plains and Midwest.
According to a 2016 study, the distinct corridor from the Upper Mississippi Valley through the Ohio Valley is most susceptible to these diseases from May through August.
“Northeastern Illinois is ground zero for progressive warm-season derecho,” said Lance Bossart, a professor emeritus at the University at Albany/SUNY and co-author of the April 2016 study with Corey Guastini.
Progressive districts in parts of Minnesota, Wisconsin, Iowa, Illinois, Indiana, southern Michigan, Ohio, Kentucky, and Appalachia averaged one to two progressive districts each May and August over the 18-year period from 1996 through 2013. , consistent with previous studies.
It can occur during the day or during the night and in the early morning hours when most people are asleep.
The number of progressive derecho events from May through August 1996-2013 that pass through a 100 km by 100 km grid square is plotted in this map above.
(Guastini and Bossart 2016)
It can be deadly. Ashley and Moti’s study found that derechos claimed 153 lives over the 18-year period of their study. Three northern states – New York (23), Michigan (17) and Ohio (16) – accounted for more than a third of Derecho’s total deaths.
Nearly 70% of deaths in Derecho occurred in areas other than permanent structures, including vehicles (30%), in boats (19%), under trees (11%) and camping (9%).
Here’s what you can do: As with any severe weather event, planning ahead and staying informed is key.
First, know where you will seek safe shelter if a National Weather Service warning is issued. If you live in a mobile or manufactured home, find a sturdy building or community shelter in advance and know how to get there quickly. The strongest derecho winds can damage or severely blow away a mobile home.
Next, we have multiple ways to receive NWS warnings, including by smartphone and from NOAA Weather Radio. These are two sources that can also wake you up if a warning is issued while you are sleeping. Make sure each is fully charged before storms arrive.
Go to shelter immediately when a warning is issued, including severe thunderstorm and tornado warnings.
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