What is a derecho? An atmospheric scientist explains these rare but dangerous storm systems

A derecho moves across central Kansas on July 3, 2005. Jim Reed/Corbis via Getty Images

Russ Schumacher, Colorado State University

Thunderstorms are common across North America, especially in warm weather months. About 10% of them become severe, meaning they produce hail 1 inch or greater in diameter, winds gusting in excess of 50 knots (57.5 miles per hour), or a tornado.

The U.S. recently has experienced two rarer events: organized lines of thunderstorms with widespread damaging winds, known as derechos.

Derechos occur fairly regularly over large parts of the U.S. each year, most commonly from April through August. Dennis Cain/NOAA

Derechos occur mainly across the central and eastern U.S., where many locations are affected one to two times per year on average. They can produce significant damage to structures and sometimes cause “blowdowns” of millions of trees. Pennsylvania and New Jersey received the brunt of a derecho on June 3, 2020, that killed four people and left nearly a million without power across the mid-Atlantic region.

In the West, derechos are less common, but Colorado – where I serve as state climatologist and director of the Colorado Climate Center – experienced a rare and powerful derecho on June 6 that generated winds exceeding 100 miles per hour in some locations. Derechos have also been observed and analyzed in many other parts of the world, including Europe, Asia and South America.

Derechos are an important and active research area in meteorology. I expect that at least one or two more will occur somewhere in the U.S. this summer. Here’s what we know about these unusual storms.

A massive derecho in June 2012 developed in northern Illinois and traveled to the mid-Atlantic coast, killing 22 and causing $4 billion to $5 billion in damages.

Walls of wind

Scientists have long recognized that organized lines of thunderstorms can produce widespread damaging winds. Gustav Hinrichs, a professor at the University of Iowa, analyzed severe winds in the 1870s and 1880s and identified that many destructive storms were produced by straight-line winds rather than by tornadoes, in which winds rotate. Because the word “tornado,” of Spanish origin, was already in common usage, Hinrichs proposed “derecho” – Spanish for “straight ahead” – for damaging windstorms not associated with tornadoes.

In 1987, meteorologists defined what qualified as a derecho. They proposed that for a storm system to be classified as a derecho, it had to produce severe winds – 57.5 mph (26 meters per second) or greater – and those intense winds had to extend over a path at least 250 miles (400 kilometers) long, with no more than three hours separating individual severe wind reports.

Derechos are almost always caused by a type of weather system known as a bow echo, which has the shape of an archer’s bow on radar images. These in turn are a specific type of mesoscale convective system, a term that describes large, organized groupings of storms.

Researchers are studying whether and how climate change is affecting weather hazards from thunderstorms. Although some aspects of mesoscale convective systems, such as the amount of rainfall they produce, are very likely to change with continued warming, it’s not yet clear how future climate change may affect the likelihood or intensity of derechos.

Speeding across the landscape

The term “derecho” vaulted into public awareness in June 2012, when one of the most destructive derechos in U.S. history formed in the Midwest and traveled some 700 miles in 12 hours, eventually making a direct impact on the Washington, D.C. area. This event killed 22 people and caused millions of power outages.

Top: Radar imagery every two hours, from 1600 UTC 29 June to 0400 UTC 30 June 2012, combined to show the progression of a derecho-producing bow echo across the central and eastern US. Bottom: Severe wind reports for the 29-30 June 2012 derecho, colored by wind speed. Schumacher and Rasmussen, 2020, adapted from Guastini and Bosart 2016, CC BY-ND

Only a few recorded derechos had occurred in the western U.S. prior to June 6, 2020. On that day, a line of strong thunderstorms developed in eastern Utah and western Colorado in the late morning. This was unusual in itself, as storms in this region tend to be less organized and occur later in the day.

The thunderstorms continued to organize and moved northeastward across the Rocky Mountains. This was even more unusual: Derecho-producing lines of storms are driven by a pool of cold air near the ground, which would typically be disrupted by a mountain range as tall as the Rockies. In this case, the line remained organized.

As the line of storms emerged to the east of the mountains, it caused widespread wind damage in the Denver metro area and northeastern Colorado. It then strengthened further as it proceeded north-northeastward across eastern Wyoming, western Nebraska and the Dakotas.

In total there were nearly 350 reports of severe winds, including 44 of 75 miles per hour (about 34 meters per second) or greater. The strongest reported gust was 110 mph at Winter Park ski area in the Colorado Rockies. Of these reports, 95 came from Colorado – by far the most severe wind reports ever from a single thunderstorm system.

Animation showing the development and evolution of the 6-7 June 2020 western derecho. Radar reflectivity is shown in the color shading, with National Weather Service warnings shown in the colored outlines (yellow polygons indicate severe thunderstorm warnings). Source: Iowa Environmental Mesonet.

Coloradans are accustomed to big weather, including strong winds in the mountains and foothills. Some of these winds are generated by flow down mountain slopes, localized thunderstorm microbursts, or even “bomb cyclones.” Western thunderstorms more commonly produce hailstorms and tornadoes, so it was very unusual to have a broad swath of the state experience damaging straight-line winds that extended from west of the Rockies all the way to the Dakotas.

Damage comparable to a hurricane

Derechos are challenging to predict. On days when derechos form, it is often uncertain whether any storms will form at all. But if they do, the chance exists for explosive development of intense winds. Forecasters did not anticipate the historic June 2012 derecho until it was already underway.

For the western derecho on June 6, 2020, outlooks showed an enhanced potential for severe storms in Nebraska and the Dakotas two to three days in advance. However, the outlooks didn’t highlight the potential for destructive winds farther south in Colorado until the morning that the derecho formed.

Once a line of storms has begun to develop, however, the National Weather Service routinely issues highly accurate severe thunderstorm warnings 30 to 60 minutes ahead of the arrival of intense winds, alerting the public to take precautions.

Communities, first responders and utilities may have only a few hours to prepare for an oncoming derecho, so it is important to know how to receive severe thunderstorm warnings, such as TV, radio and smartphone alerts, and to take these warnings seriously. Tornadoes and tornado warnings often get the most attention, but lines of severe thunderstorms can also pack a major punch.

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Russ Schumacher, Associate Professor of Atmospheric Science and Colorado State Climatologist, Colorado State University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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33 thoughts on “What is a derecho? An atmospheric scientist explains these rare but dangerous storm systems

  1. ‘most destructive in US History’ and so US History includes – dates please – this is science –
    S
    ince the 1987 publication, the term derecho has become more commonly used
    in describing long lived convective straight-line wind events that have occurred
    and many research studies have been directed towards derecho events.
    Derecho events have been documented in North America (e.g. Duke and
    Rogash 1992; Alfonso and Naranjo 1996; Wolf 2000) and, more recently,
    derechos have been documented in Europe (e.g. Gatzen 2004; Punkka et al.
    2006). As time progresses, it is likely that these events will be found to have
    occurred in many other areas of the world. Besides documentation of derecho
    occurrence, research studies have also examined the climatology and hazards of
    derechos in the United States (e.g. Bentley and Sparks 2003; Coniglio and
    Stensrud 2004; Ashley and Mote 2005) and determined the weather patterns
    (e.g. Johns and Hirt 1987; Coniglio et al. 2004) and meteorological conditions
    (e.g. Evans and Doswell 2001; Doswell and Evans 2003) associated with
    derecho events.
    URL below is likely the best history you’re gunna get on derechos;
    https://www.spc.noaa.gov/misc/AbtDerechos/hinrichs/JohnsDerechoStory.pdf

  2. But aren’t Derechos made worser/badder/bigger by the Climate Scam? Some how they must be. The climate religion dogma demands it be so.

    Referring to the Climate Priesthood for guidance, NASA sez:
    “Scientists have evidence that global warming should increase CAPE (convective available potential energy (CAPE) and strong wind shear. CAPE is a measure of how much raw energy is available for storms ) by warming the surface and putting more moisture in the air through evaporation. On the other hand, disproportionate warming in the Arctic should lead to less wind shear in mid-latitude areas prone to severe thunderstorms. So one factor makes severe storms more likely, while the other makes them less so.”
    https://climate.nasa.gov/news/897/severe-thunderstorms-and-climate-change/

    Note: The use of “should”, not “will” by NASA. Evidence simply “is.” But Speculation is “should.”
    What we have is speculation from models about Derechos and the Climate Scam.

    • “Note: The use of “should”, not “will” by NASA.”

      Yes, that jumped right out at me.

      NASA Climate needs to get some evidence for Human-caused Climate Change before they go claiming it “should” do something to enhance storms.

      First things first, NASA Climate.

    • Yes, I think it would be better for them to look at the jet streams as a cause, rather than human-caused climate change. Jet Streams are real. Whereas, there is no evidence that Human-caused Climate Change is real.

    • Gosh, “derecho” is so much scarier than “squall line” with which any old-school mariner or aviator is familiar.

  3. der echo
    de·re·cho
    /dāˈrāˌCHō/

    nounUS
    noun: derecho; plural noun: derechos
    a line of intense, widespread, and fast-moving windstorms and sometimes thunderstorms that moves across a great distance and is characterized by damaging winds.
    Origin

    late 19th century: Spanish, literally ‘direct, straight’.

    Notice that it is a NOUN, not a verb. Therefore it serves no purpose in the climatesham as it is not actionable. /sarc

    Ok so, a line of fast moving thunderstorms over a great distance. This we know, derecho definition we know…so what exactly IS the point of this article again? Oh wait, I think I found it in this tidbit:
    “where I serve as state climatologist and director of the Colorado Climate Center “

  4. My niece and her husband live on a ranch in southern Campbell County in NE Wyoming. Here’s what she said of the 6/6/2020 event; “We have had horrendous weather!! Yesterday a terrible wind that doplar (said) was 100 mph gusts…we had live trees galore down and buildings blown apart. Really a crappy day. I think I am done with trying to get trees to grow around here. ”

    And after I emailed her with pictures of the snow on the ground here in SW WY on 2/17/2020, she emailed back; “Brrr..it felt like fall here this morning too. My plants and garden look like hell, mostly the drying wind we’ve had. We have zero grass for the cows too. Our fields are a total loss. Always a gamble this way of life in this harsh country.”

    Not a fun year on the ranch.

    Take care,

  5. I was on my sailboat coming into West River south of Annapolis when the June 2012 Derecho came through. I was on deck trying to get the spare halyard that had wrapped around the Genoa undone so I could get the Genoa furled. The wind was blowing pretty hard, everything was flapping and it was just myself and my wife on board. I finally ended up cutting the halyard, pulling it through the sail and got the sail furled.

    About that time the Coast Guard came on the VHF with an urgent marine warning. You could see the dark off on the horizon and we got to the slip about the time you could see the roll cloud leading the way coming fast. Fortunately there were a few helpful souls on the dock there to help secure the boat. I literally tied the last line, ran to the companionway, slid the cover closed and all Hell broke loose. It was over in 10 minutes, but something I’ll never forget. Quite a display of wind and rain.

    • Imagine what it was like back in the days of sail when they didn’t even have a barometer, let alone radio communications and radar.

  6. They used to be called “Squall iines.” I’ve experienced several in the NW US. Palouse praire of E.Washington, an d also one of the most memorable was in NE Oregon in 1974-when a fast moving system ran over the are causing widespread “Straight wind damage to several towns.
    but it was a ‘squall line’ not a ‘Dericho.
    BTW I was a NOAA certified weather observer then..

    • A derecho is a squall line, but not all squall lines are Derechos. Similarly a hurricane is a tropical cyclone, but not all torpical cyclones are hurricanes.

    • ‘The lie-storm clouds fly tattered and swift,
      the road is forlorn all day,
      where a myriad snowy quartz stones lift,
      and the hoof prints vanish away.’
      Robert Frost
      Have wondered if this is an old reference to the
      same weather phenomena.

  7. Thankfully on the day that Derecho mentioned came through our place about 35 mi. NNE of Indianapolis this truck driver was driving west of it up I-39 headed for Peru, IL. When I got back home my wife and I spent hours cleaning up the deadfall and broken limbs in the yard before I could mow my acre. Five birds nests on the ground among the other debris.

    Years ago when I was driving for Schneider I was in western Kansas and saw one of those things coming and found a place to park the rig between two dropped trailers before it hit. It really rocked my rig even though I had a heavy load. There aren’t many times the weather has stopped me in my 16+ years behind the wheel of a big truck doing OTR, but it is just asking for it to try and drive through one of those super squall lines.

    When Joplin, MO got hit with that massive F-5 I was on I-70 in that state headed for KC. Tuned to the National Weather Service radio, I heard reports of tornadoes on the ground behind me and ahead of me. I only pulled over once just short of Boone, a few miles west of Columbia when dime sized hail and a tornado warning with the DC sirens wailing prompted me to let the storm pass.

  8. I like the Australian sailor’s name for these events a lot better. They call them “weather bombs”. I experienced one of these weather bombs in Puerto Vallarta, Mexico one year, while anchored out in Bandaras Bay. The winds went from 15 knots to 70 in a matter of minutes. Lots of boats dragged their anchors and even the marina had a lot of damage. It lasted about 4 hours.

  9. Sure am glad that there is a name for thing that that mangled the passenger door of my 1974 Fiat 128 in 1976 near Rantoul Illinois.

    • Wow! Another fool who owned a 1974 Fiat 128! I had mine for less than a year and traded it for a just introduced Honda Accord hatchback. Talk about night and day.

      I’ve had a few bombs in my day, but the Fiat 128 was no doubt the worse. Could not shift it smoothly and it was subject to carburetor ice. Had to get out in the rain and turn the air cleaner over (per the operator manual) when it started sputtering. Not a clue why I bought it.

      • Boo. I loved the Fiat 128. Not exactly reliable but a great drive (lack of power meant you didn’t need to back off much through corners).

        I didn’t know they sold any in North America

  10. An interesting and informative article; I’ve learned something new. Thanks to CTM for posting it; I would never have seen it otherwise.

  11. Isn’t this what we call a plow wind in western canada?
    Straight line strong winds produced by thunderstorms that plow over houses, bins, trees etc

  12. It’s funny how people are…1) we experience something (bad storms) and kind of shrug them off. 2) Then someone smart recognizes they come in degrees of strength and so name them, and now people have a label to put on them. 3) Then every time one occurs, people now recognize it by name and it seems to happen more often. 4) Then news media starts pointing them out and the damage they cause is all over their news. 5) And the final piece is the climate agitators then make a wild claim that they are caused by CO2 and its worse than we thought.

    We seem to be at step 3 or perhaps entering step 4 at the moment.

    I for one enjoyed this article just for the learning experience.

  13. We live in Central Ohio. We saw the June 2012 derecho up close and personal. It was very impressive, Snapped some trees on the other side of our street like matchsticks and downed the power lines. We were without power for 4 days.

    We live in town and we never get tornadoes in our neighborhood. I think the UHI kills them. But the derecho blew though like nobody’s business.

  14. I learned about derechoes firsthand eight years ago. Back in ’12 the wife and I bought the house in which we plan to spend the rest of our lives. Afternoon of the closing we’re sitting on the covered back deck looking out at the wonderful, mature trees covering our acreage. I remember saying to her, “Take a good look, honey. Everything you can see belongs to you. Not the bank, not a mortgage company. All those trees are yours.”

    About eight hours later, thanks to the derecho that came through our area that night, we were about six trees shy of what we had that afternoon. No power for five days, and sundry other complications to settling in to country living ensured.

    Of course, it took what some folks called Superstorm Sandy exactly four months to the day later to convince me it was time to purchase a whole house generator, and other survival oriented accessories.

    Naturally, Mr. Murphy ensured that, once I’d made all the preparations for potential weather-related disasters we’ve had nothing like those four months since.

    Other than, of course, the time that Climate Change killed off our entire stand of ten year-old Crepe Myrtle trees one winter. As I mentioned to my wife the morning after our historic freezing temperatures that spelled the crepe myrtles’ doom, “Thank Heavens for AGW! Can you imagine the devastation we’d’ve had if the climate weren’t getting warmer?!”

  15. I live in Akron, Colorado and one of these storms did a number on us last June 9th. Hundreds of power poles down… thousands of trees destroyed… it destroyed hundreds of grain bins… tore many, many farmsteads apart…. The USDA Experiment Station East of town measured the wind at 112 mph. It sure put a world of hurt on our humble little town and the surrounding area. It was also interesting that it made international news 36 hours before the front range radio and television stations even mentioned it. The seven front range counties are all that matters in Colorado any more. They are so much smarter and important than the rest of the state.

  16. We had one in northern WI last summer in late July. The TV said 100+ mph straight line winds. I believe it.
    It was devastating for a huge area. Tens (or hundreds) of thousands of trees got taken down in the Nicolet National Forest and many of the towns around here. It went through a bluegrass festival and just leveled the place. Area towns were out of power for days, and there was a huge relief effort to get roads cleared and to get people food & water. They are still cleaning up roads and trails in the Nicolet, and there is a massive salvage logging operation ongoing.
    I knew something really bad was going to happen that day with 4,000+ CAPE and 40+ shear, but I had expected tornadoes. Surprise. It was much worse as it hit such a large area.
    I got very lucky. The storm ran out of gas at sunset about 10 miles west of my house. There was rotation on the Doppler that close and just poof! Nothing.

  17. What are the down blasting storms like the one that knocked down all the trees at Versailles some years ago? There was another one a few miles west of Mammoth Lakes that knocked down a huge section of forest.

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