On This Day: The 2012 Midwest/Mid-Atlantic Derecho | WeatherBug
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On This Day: The 2012 Midwest/Mid-Atlantic Derecho

June 28, 2022
By WeatherBug Meteorologist, Andrew Rosenthal
Like a bulldozer tearing across the Midwest and Mid-Atlantic, the derecho of June 2012 ripped a path both in the ground and in the memories of residents of the Eastern U.S. One of the strongest and longest-lived storms of its type, it killed dozens while causing damage into the billions of dollars.
 
First off, what is a derecho? The term is derived from the Spanish word for straight, and meteorologically that is an apt description. It is a long-lived, widespread series of thunderstorms that produce strong straight-line winds (as opposed to the spinning winds associated with a tornado). Specifically, to be called a derecho, wind gusts of 57 mph or higher must be found in a single set of storms over an area 60 miles wide and 250 miles long.
 
Derechos are typically found across the Plains, Ohio Valley, Mid-Atlantic and Northeast in the late spring and early summer, as the weather setup for a derecho are typically similar. Widespread very warm air fuels the atmosphere to initially develop strong thunderstorms. As the storms advance over time, their strong winds feed the storms’ engine with additional warm air, allowing the storm to maintain itself for significant lengths of real estate.
 
The derecho of Friday, June 29, 2012, was a typical case. Strong high pressure was locked in place across the upper Tennessee Valley, with a cold front stalling from Illinois to Pennsylvania. Strong southwesterly winds around the western side of the high pushed very warm and humid air into the Ohio Valley and Mid-Atlantic. Temperatures cracked the triple-digit mark from Baltimore and Washington, D.C., to the Ohio Valley in West Virginia, Ohio and Kentucky. The other ingredient came about from a weak disturbance pinned to the front in Iowa that Friday morning.
 
As the disturbance started rolling eastward that morning, it fed off the muggy airmass in place across the Midwest, busting across the Chicagoland and northern Indiana with wind gusts as high as 91 mph in Fort Wayne, Ind., during the early afternoon. By late afternoon, the developing line of storms had reached central Ohio, and turned into a beast as the gusty winds expanded across the Buckeye State.
 
Thanks to the hot and humid airmass, the storms were able to maintain their strength as they approached the Appalachians, surprising government forecasters that had only anticipated scattered strong storms. A Moderate Risk – the second highest level of storm risk – was hastily issued for the region. Meanwhile, putting the pedal to the metal, the storm's forward motion increased to as much as 60 to 70 mph. This made it difficult for forecasters to keep up with watches and warnings, limiting warning time to 30 minutes or less in many cases.
 
The storms roared across the Appalachians and into the Mid-Atlantic as day turned to night, racing along the Interstate 70 corridor toward the Nation’s Capital. Widespread wind gusts of 65 to 80 mph spread from central Maryland to northern and central Virginia between 8 and 10 p.m., which coupled with constant lightning knocked out electricity to the region. The storms continued into southeastern Virginia, the Delmarva and southern New Jersey as Midnight approached before finally abating as they entered the western Atlantic.
 
Immense doesn’t even begin to describe the impact of the storms. The limited warning time left campers exposed to the dangerous winds, and numerous people were killed when trees fell on their tents that evening. More than a million Virginians, and nearly as many Marylanders and Ohioans were without power following the storm. At the peak, electricity outages from Indiana to New Jersey exceeded 5 million customers.
 
As if the storm itself wasn’t bad enough, the stubborn high pressure system maintained the hot, humid weather pattern for the subsequent week across the region, ultimately leading to 34 heat-related fatalities through July 9 as people were unable to access air conditioning and neighborhood cooling centers became overwhelmed. By the time damage was calculated, it was estimated at 2.2 billion dollars.
 
Brutal derechos are not particularly rare across the Midwest – for example, another one in August 2020 caused an estimated $7.5 billion damage as it cut power to the entirety of Cedar Rapids, Iowa, and tore across the Chicagoland. Cornfields were shredded and the storm demolished grain-storage units. However, due to the damage and compounding heat, the 2012 derecho ranks among the top impacting weather events of the century.

Story Image: A shelf cloud from the developing storm near LaPorte, Ind., on the afternoon of June 29, 2012. (Kevin Gould, NOAA)