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The Tetchy History of Derecho Science

A derecho, a massive, powerful straight-line storm, barrelled through the U.S. state of Iowa on August 10, 2020, shocking the residents and the nation with its power and destructive capability. This Background Check discusses what are derechos, how they got their Spanish name, and how two cranky 19th-century gentlemen brought about their definition.

Map from 'Tornadoes and Derechos, Gustaves Hinrichs 1888
Map published by Gustaves Hinrichs 1888 in direct rebuttal to John Park Finley, in which he named derechos

What is a Derecho?

A derecho (de-RAY-Cho), or more officially, a derecho-producing convective system (DCS, and a subset of mesoscale convective systems), produces large swatches of severe straight-line winds at the earth's surface. They're found all over the world, but most often in the plains and midwest states of the U.S. The storms were named after derecho, a Spanish word meaning lots of things but in this context "straight" or "direct." It was Spanish because what we've forgotten at this point is "tornado" is Spanish. Or rather, bastardized Spanish: tornado was a word coined by British sailors in the late 16th century from the Spanish words tronada (meaning storm) and tornar (to twist) to refer to oceanic storms, with an "o" tacked onto the end for, uh, jolliness.

When the 19th-century physics professor Gustaves Hinrichs (1836–1923) picked derecho to mean "straight-line storm," the western world was in the throes of the scientific revolution, when words began to take on finer definitions. Twister, tornado, hurricane, thunderstorm, all were words that had been around for a while but could be used interchangeably. The words took on more and more specific meanings as scientists developed the language to differentiate among them.

Hinrichs described them thusly:
  • The derecho, or "straight blow of the prairies," is a powerfully depressing and violently progressing mass of cold air, moving destructively onward in slightly diverging straight lines (in Iowa) generally towards the southeast, with its storm-cloud front curving as the storm-lines diverge. The barometer bounds upwards and the thermometer falls greatly under the flow of this cold air in the upper strata suddenly striking the ground. The derecho will blow a train of cars from its track, unroof, overturn and destroy houses: but it does not twist the timbers into splinters and drive them firmly into the hard soil of the prairies." (Hinrichs 1888).

Discovery and Dispute

The first person to publish detailed information about derechos was not Hinrichs, but John Park Finley (1854–1943), a man who worked in the U.S. Signal Corps and had an intense obsession with tornadoes. The Signal Corps was a branch of the U.S. Army (still is) which was in the business of forecasting weather. Finley became convinced that one could predict storms. Although he never got to the prediction stage, Finley collected an enormous amount of data in his day job and out of it by traveling through the midwest and plains eventually enlisting 2,400 unpaid storm spotters.

In 1888, the Signal Corps allowed Finley to publish a paper for the U.S. Bureau of Statistics enumerating storms in Iowa between 1837–1887, a paper that came to the attention of Gustaves Hinrichs. Hinrichs was the head and founder of the Physics Department at the University of Iowa, who studied an enormous range of things including weather and so had his own army of tornado spotters. Hinrichs was enraged (he was that sort of guy) because Finley had the nerve to publish without citing Hinrichs' work, and because Finley was listing too many tornadoes, an "outrageous blunder" which "causes sensational fright to our own people, driving them into expensive tornado insurance, and scaring eastern people from coming to Iowa."

Finley was counting derechos along with tornadoes, and further he was counting them as several different events–it's a quite modern argument about how you count storms, tracking them over wide-ranging movements ("named storms") or single event at a city or town. It was Hinrichs who defined derecho as the straight-line type of storm separate from the twister form of tornado. Whether that reduced the fright in people is debatable: Certainly, the Signal Corps attempted to suppress the data so people wouldn't be so frightened.

Both of these men were brilliant and difficult, but in the end, both men lost their jobs, not (just) because they were difficult to get along with, abrasive, argumentative, and demanding. Finley got fired, caught up in the still-perennial battle over whether the weather service should be led and paid for by private or public institutions. Hinrichs lost his lab and students and finally his job in the perennial battle of university administrators who favored humanities over science.

Suppression

In the late 19th century when this took place, there was a revolution going on. Charles Darwin's Origin of the Species had affronted many in and out of the scientific community and there was an anti-science backlash that struck both of these men. After Hinrichs' blistering attack, things got so bad in the weather service that the Signal Corps attempted to suppress the use of the word "tornado." It didn't help that the scientists fought blistering battles among themselves for the control of obscure bits of knowledge, trying to resolve issues that are still in play today.

Although "tornado" was never dropped—it was firmly in the literature and the people's experience and understanding—but the word "derecho" was effectively dropped. Focused study on these types of storms was delayed until 1987 when meteorologists Robert H. Johns and William D. Hirt brought them back to the attention of the scientific community and the rest of us.

Coda

The history of the discovery and definition of derecho type storms is stormy in and of itself, a snapshot of the changes that occurred as a result of the birth pangs of modern science. Regardless of their own commitment to the studies, Hinrichs, in particular, played a role in the academic end of the battle, while Finley represented the military and governmental end. It is a battle that we know all too well today.

You're probably wondering whether derechos will be impacted by climate change. They've definitely been around for a long time. In the website Facts about Derechos, written by meteorologist Stephen Corfidi and colleagues, and published at NOAA's Storm Prediction Center, the scholars say that it's hard to know what global warming will do. But,

  • What can be said with greater certainty about derechos and climate change is that the corridors of maximum derecho frequency likely would shift poleward with time. This is because the bands of fast upper-level winds that arise from the equator-to-pole temperature gradient–the jet stream–would contract poleward in a warmer world. Because derechos tend to form on the equatorward side of jet streams, especially those that mark the northern fringes of warm high-pressure ("fair weather") systems, the areas most favored for derecho development also would shift poleward. Corfidi et al. 2018

Sources and Further Reading

I highly recommend the report by meteorologist Robert H. Johns, Origin and Evolution of the Term “Derecho” as a Severe Weather Event. Freely accessible, completely readable, and informative about the history of derecho research. I can't imagine why no one has formally published it yet.


Created by KKris. Last Modification: Tuesday 18 of August, 2020 10:30:50 EDT by KKris.