D.C.’s Infamous 2012 Derecho

 

June 2012 Derecho (Source: NOAA)

Today marks 11 years since one of DC’s most destructive severe weather events.   It’s safe to say that prior to the evening of June 29, 2012, most Washingtonians had never heard the meteorological term “derecho.”  That date will forever live in weather infamy in the nation’s capital because a “derecho” knocked out power to more than a million people in the DC Metro Area. 

D.C.’s hottest June day on record was June 29, 2012 with a high temperature of 104°.  There was also a high degree of atmospheric instability, which helped create the ideal environment for severe thunderstorms.  Consequently, area meteorologists grew increasingly apprehensive as a cluster of severe thunderstorms developed over eastern Iowa and northern Illinois on the morning on June 29.  Thunderstorms within the cluster quickly reached severe limits and tracked eastward as the day wore on. 

“Derechos” are a type of squall line.  A “squall line” is a line of thunderstorms that can become severe, with the primary threat often being wind gusts of at least 58 mph.  “Derechos” are longer lasting squall lines that travel at least 240 miles, according to NOAA’s Storm Prediction Center.  Wind gusts in a derecho are typically higher than 58 mph but less than 100 mph.  Such was the case when the June 2012 derecho passed through the Mid-Atlantic Region.  The highest wind gusts in the D.C. Area were 71 mph at Dulles Airport, 70 mph at National Airport, and 66 mph at BWI Airport. 

Overall, the highest wind gust in the 2012 derecho was 91 mph in Fort Wayne, Indiana.  That is equivalent to the wind in an EF-1 tornado.  Unlike other types of thunderstorms, the primary type of damage that occurs in derechos are from straight-line winds.  That’s generally easy for experts to determine as the majority of damage occurs in linear fashion. 

The June 29, 2012 derecho came through the D.C. Metro Area between 9:00 – 11:30 at night.  It knocked down countless trees and power lines, which created one of the largest power outages on record.  Many roads were impassable and treacherous.  Normally, it takes me less than 20 minutes to drive home after work, but it took more than an hour to navigate the roads that night.  According to NOAA, there were 13 fatalities during the event combined with an estimated total of 4 million customers without power for a week, from the Midwest to the East Coast.

Not until the next morning, a Saturday, did Washingtonians fully appreciate how damaging the derecho was.  The extensive tree damage even caused Saturday’s round of the AT&T National golf tournament at Congressional Country Club in Bethesda, Maryland, to be closed to the public.  Adding to the hardship of the widespread power outages was an extended heat wave with highs of at least 95° at National Airport every day through July 8.