DISCUSSION: If you live anywhere other than tornado-prone areas, you’ve probably never heard of the term “derecho”. According to The National Weather Service, a derecho is classified as a widespread, long-lived, straight-line wind storm that is associated with a fast-moving group of severe thunderstorms. These storms are known for traveling along a path of at least 240 miles, and contain wind speeds of 57 MPH (or 50 knots) as well as gusts that can exceed over 100 MPH (or 87 knots).
These violent storms are known for their bow-shaped looking structure, as shown in the image below. This shaped is caused by the strong flow at the rear of the system. This “flow” is movement of air from one area to another. The primary cause of airstream flow is the existence of pressure gradients. Air behaves in a fluid manner, meaning particles naturally flow from areas of higher pressure to areas of lower pressure. Thunderstorms flourish on warm, moist air due to the fact that warm, moist is the primary “fuel source” which drives the development and maintenance of convective updrafts. As a result, the majority of derechos occur during the hot, humid days of summer.
Image Courtesy of:
http://www.spc.noaa.gov/misc/AbtDerechos/images/2012jun29/12jun29_composite.png (**Numbers represent preliminary wind gust reports**)
During the mid-summer days of June 29th into June 30th, 2012, a very destructive and long-tracked derecho hit areas of the Ohio Valley and Mid-Atlantic regions of the United States. This particular storm created a swath of damage of over 600 miles long, resulting in a total of 22 deaths, power outages affecting millions and a damage total of $2.9 billion.
This particular derecho originally started as a storm in Iowa causing severe hail in many spots. It worked its way eastward towards Indiana with day-time heat indices approaching 100°F helped to fuel this storm. Storms forming to the south in Indiana began to help fuel the parent storm, or in other words the original storm, as surface heating destabilized the region. These two systems intensified as they clashed into each other and worked their way towards Ohio. Wind gusts of over 90 MPH (or 78.2 knots) were reported in Indiana, as well as upwards of 84 MPH (or 73 knots) in Ohio; both of which were recorded near the time at which the event was at its peak magnitude. As the storm approached the Appalachian Mountains, it began to weaken. Once it entered the Washington D.C. metro area, the storm regained momentum and produced wind gusts of 65 - 75 MPH (or 56.4 - 65.1 knots), and slowly started to fall apart as it hit the Chesapeake bay and open waters.
The significance of this storm shows that when the conditions are favorable, derechoes can work their way from the mid-western portion of the United States towards the East Coast. While this event wasn’t the first to hit many of these areas, this was one that was a steady reminder that they can happen almost anywhere in the lower 48 states!
You can learn more about derechoes as well as this particular event here http://www.spc.noaa.gov/misc/AbtDerechos/casepages/jun292012page.htm!
To learn more about other high-impact severe weather events (both past and present), be sure to click here!
© 2018 Weather Forecaster Michael Ames