Destructive and Rare: DC Derecho Two Years Later

The last several years have certainly featured some unique weather in parts of the country unaccustomed to seeing it.  From extreme and prolonged drought across much of the western and south central United States to more frequent and more destructive rounds of severe weather – whether tornadoes, high winds or large hail.  Before two years ago, the term “derecho” was also outside the lexicon of weather terminology for those living on the East Coast.

Most Mid-Atlantic residents will remember two major weather events that occurred two years ago this week.  Not only was June 29, 2012, the hottest June day on record in the Nation’s Capital with a daily and monthly record high of 104 degrees but it was also the day of an infamous “derecho.”  In meteorology, a “derecho” is a long lasting line of fast moving thunderstorms that features damaging winds.  Quite often the winds exceed severe criteria gusting in excess of 58 mph.

The combination of record heat and atmospheric instability made conditions ideal two years ago today for the “derecho” to not only form but remain intense as it traveled hundreds of miles from the Ohio Valley to the Mid-Atlantic Coast.  People could track the line of storms on radar as it moved rapidly eastward during the afternoon and early evening.

Shortly after dark when the “derecho” moved through the Mid-Atlantic Region, the National Weather Service recorded many severe wind gusts between 60 and 80 mph.  That resulted in power outages to millions of people as well as several fatalities – largely the result of falling trees – around the Nation’s Capital.  Since so many trees and power lines were knocked down by the “derecho,” it took power crews almost a week to restore power to the majority of customers in the Mid-Atlantic. 

Making matters worse was the fact that June 29, 2012, was only the second day of an 11 day stretch with high temperatures of at least 95 degrees in the Nation’s Capital.  In fact, between June 28 and July 8, 2012, there were 5 days that reached 100 degrees or hotter in Washington, D.C.  The extreme heat combined with the extended power outages created a great deal of hardship for residents of Maryland, Virginia and the District of Columbia. 

Fortunately, “derecho’s” are exceptionally rare in the Mid-Atlantic Region and the majority of weak or damaged trees were either knocked down during the “derecho” or cut down in the process of restoring power.  So by the time “Superstorm” Sandy impacted the Mid-Atlantic Region four months later, there were significantly fewer power outages due to improved infrastructure.

Improved weather satellite and computer modeling technology has allowed for better weather forecasts.  This allows scientists to issue more timely weather watches and warnings for a wide range of weather events ranging from severe weather to tropical storms and hurricanes.  Fortunately, no record setting heat or severe weather is expected in the Mid-Atlantic Region this week.