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 three 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. And on August 10, a derecho rolled across Iowa, Wisconsin, Illinois and Indiana, generating rare “particularly dangerous situation” warnings from forecasters and registering wind gusts as high as 130 miles per hour.

Derechos have also been observed and analyzed in many other parts of the world, including Europe, Asia and South America. They are an important and active research area in meteorology. 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.

This is an updated version of an article originally published on June 15, 2020.

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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.

From Kangaroo Island to Mallacoota, citizen scientists proved vital to Australia’s bushfire recovery


Alan Finkel, Office of the Chief Scientist and Erin Roger, CSIRO

Following the Black Summer bushfires of 2019-20, many people throughout Australia, and across the world, wanted to know how they could help in response to the environmental disaster.

Hundreds contacted the Australian Citizen Science Association (ACSA), Australia’s peak citizen science body, for guidance on how to participate in relevant scientific projects.

It was a golden opportunity to show that science can be, and is, done by all kinds of people – not just those working in labs with years of training and access to high-powered instruments. A scientist can be you, your children or your parents.

And this recognition led to the establishment of the Citizen Science Bushfire Project Finder, a key outcome from the bushfire science roundtable, which was convened in January by Federal Science Minister Karen Andrews.

To establish the project finder database, ACSA partnered with the CSIRO and the Atlas of Living Australia to assist the search for vetted projects that could contribute to our understanding of post-bushfire recovery.

Five months on, the value is evident.

Science as a way of thinking

In response to the bushfires, one citizen science project set up was the Kangaroo Island Dunnart Survey. A record number of citizen scientists answered the call to assist in recovery efforts for this small marsupial.

The Kangaroo Island dunnart was already listed as endangered before the fires, with population estimates between 300-500 individuals. And initial post-fire assessments indicated a significant further decline in its population, highlighting the importance of tracking the species’ recovery.

Meanwhile, nearly 1,500 kilometres away from Kangaroo Island, a local resident set up “Mallacoota After Fires” in the small community of Mallacoota, Victoria – a region hit hard by the bushfires.

This has enabled the community to record and validate (via an app and website) how the fires impacted the region’s plants and animals.

So far, the project has documented the existence of a range of flora and fauna, from common wombats to the vulnerable green and golden bell frog. It has also captured some amazing images of bush regeneration after fire.

Science does not just belong to professionals. As eminent US astronomer Carl Sagan noted, “science is a way of thinking much more than it is a body of knowledge”.

This suggests that, when properly enabled, anyone can actively participate. And the output goes beyond the rewards of personal involvement. It contributes to better science.




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The need for ongoing engagement

Citizen science is significantly contributing observations and expertise to bushfire research. Across southeast New South Wales and the ACT, several hundred citizen scientists have:

  • conducted targeted landscape-wide surveys of threatened species, or new weed or pest incursions
  • collected specified data from plot locations stratified against fire history
  • assessed whether wildlife actually use water and feed stations established by communities after a fire has been through. (Data suggests the use of the stations is limited).

And it’s not just in local communities. Platforms such as DigiVol have enabled citizen scientists from around the world to review thousands of camera trap images deployed post-fire to monitor species survival and recovery.

Still, there is much more to do. Australia is a vast continent and as we saw last summer, the fire footprint is immense.

But there is also a huge community out there that can help support the implementation of science and technology, as we adapt to our changing climate.

Reaching out at the right time

In January, Prime Minister Scott Morrison asked the CSIRO, supported by an expert advisory panel chaired by one of us (Alan Finkel), to develop recommendations for practical measures that would increase Australia’s disaster and climate resilience.

The report on Climate and Disaster Resilience gives due emphasis to the importance of citizen science in complementing traditional research-led monitoring campaigns and sharing locally specific advice. One component of the response also brought together national stakeholders, to develop a series of more detailed recommendations regarding the critical role of citizen science.

Citizen scientists can be involved in important data collection and knowledge building. They can collaborate with disaster response agencies and research agencies, to develop additional science-based community education and training programs.

Also, citizen science is a way to collect distributed data beyond the affordability and resources of conventional science.

With that in mind, the task now is to better marry the “professional” scientific effort with the citizen science effort, to truly harness the potential of citizen science. In doing so, we can ensure environmental and societal approaches to disaster recovery represent a diversity of voices.

The role of the community, particularly in developing resilience against environmental disaster, can be a most useful mechanism for empowering people who may otherwise feel at a loss from the impact of disaster. Furthermore, by working with communities directly affected by bushfires, we can help measure the extent of the impact.

We call on our professional scientist colleagues to actively collaborate with citizen science groups. In doing so, we can identify priority areas with critical data needs, while also informing, enriching and engaging with diverse communities in science.

Equally, we encourage citizen scientists to share and tell their stories across social and political settings to demonstrate the impact they continue to have.

The beneficiary will be science.




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The Conversation


Alan Finkel, Australia’s Chief Scientist, Office of the Chief Scientist and Erin Roger, Citizen Science Program Lead, CSIRO

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