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Cyclone of groan

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Posted: Jun 4, 2014 10:42 AM by Meteorologist Josh Eachus
Updated: Jun 4, 2014 10:42 AM
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  Rating: 5.0 (4 votes)

Topics: weather, inland hurricane, derecho, wind

The latest weather buzzword has again left fatigued forecasters to cringe with heads in hands.

Unlike El Niño and Polar Vortex, two meteorologically accepted terms that were battered beyond recognition, print and broadcast journalists have now created their own insidious word, especially so considering the true definition of its namesake.

Introducing, the "INLAND HURRICANE."

When early week computer forecast models and radar simulations began hinting that a significant storm event would occur late Tuesday in the Upper Midwest, one broadcaster in that region tweeted, "it's called a land hurricane." This was an out-of-context likening to a rare type of large scale wind event known as a derecho. However, outside of the possible consequences from wind damage, the similarities between a hurricane and derecho end.

The National Weather Service Storm Prediction Center defines a derecho (deh-RAY-cho) as "a widespread, long-lived wind storm. Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems." The SPC furthers the definition with, "Although a derecho can produce destruction similar to that of a tornado, the damage typically occurs in one direction along a relatively straight path. As a result, the term 'straight-line wind damage' sometimes is used to describe derecho damage. By definition, if the swath of wind damage extends for more than 240 miles, includes wind gusts of at least 58 mph along most of its length, and several, well-separated 75 mph or greater gusts, then the event may be classified as a derecho."

Certainly the aftermath of such an event may look like that of powerful hurricane winds. But the structure and organization of the two storms is entirely different.

A derecho originates from a bow-echo. Bow echoes occur when rain cooled air from a cluster of thunderstorms reaches the surface and advances horizontally with the wind flow. This advancing cooler air forces additional warm, moist air upward into cold air and propagates the storm downwind. These continental systems are almost always cold-cored, or below freezing in the upper levels.

Hurricanes develop over large bodies of water as warm, humid air rises into relatively cooler air above, generating clusters of thunderstorms. As air exits the surface, less air and thus lower pressure develop. Because air travels from higher to lower pressures, air continues flowing into this low pressure center, it too rises and the surrounding air wraps in from all directions to take its place. If the process continues uninterrupted, eventually the storm will begin to rotate counterclockwise, tighten, develop an eye and become a hurricane. Maritime or sea-based tropical systems typically have a warm core, or are above freezing in the upper levels.

Despite clear meteorological differences, the term "INLAND HURRICANE" has stuck. Various internet searches of the new buzzword will return recent results for Tuesday Evening's weather event. Furthermore, broadcast news pieces across the nation are pumping the phrase and causing a cyclone of groan for weather-types.

To the credit of the broadcaster who mentioned the term earlier this week, they may not have "coined" it. After extremely high non-tornadic wind damage and a highly unusual radar signature (graphic attached) associated with the Southern Missouri/ Southwestern Illinois DERECHO OF May 2009, many labeled the event an "INLAND HURRICANE." The radar image indeed displays somewhat of a tropical cyclone-like swirl and eye-like center. Nevertheless, forecasters would later; more appropriately, deem the storm a "super derecho."

The May 2009 event and an expansive damaging wind storm that cut power to millions from Indiana to Maryland in June 2012 were the last two significant derechos in United States history. As of this writing, there has not been official word from the National Weather Service declaring Tuesday Evening's storm a derecho.

Whether it was sinless sensationalizing or hapless hyperbole, this latest weather axiom has stormed its way through many newsrooms leaving station meteorologists just across the building feeling so much farther away.

You can get forecasts from Meteorologist Josh Eachus weekdays on 2une-In from 5-7am and News 2 at Noon from 12-1pm. Additionally, you can get the fastest and latest forecasts and weather news by checking in with wbrz.com/weather, liking Josh on Facebook and following him on Twitter.

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