Between 9:30 and 11 p.m. Friday night, one of the most destructive complexes of thunderstorms in memory swept through the entire D.C. area. Packing wind gusts of 60-80 mph, the storm produced extensive damage, downing hundreds of trees, and leaving more than 1 million area-residents without power.
Racing along at speeds over 60 mph, the bowing line of thunderstorms formed west of Chicago around 11 a.m. and by midnight approached the Atlantic ocean. It left a massive trail of destruction spanning from northern Illinois to the Delmarva Peninsula. The National Weather Service has logged well over 800 reports of damaging winds.
This kind of fast-moving, long-lived, large, and violent thunderstorm complex is known as a derecho.
Incredible radar loop of derecho from start to finish uploaded to YouTube by akrherz
Derechos are most common in the Midwest and Great Lakes between May and July. The National Weather Service indicates they occur about once every four years in the D.C. area.
Link: Facts about derechos
They often form along the northern boundary of a hot air mass, right along or just south of the jet stream - where upper level winds zip along at high speeds.
During summer, the jet stream atop a sprawling heat dome is sometimes called a “ring of fire” due to the tendency for explosive thunderstorms to form along this weather front separating hot, humid air to the south and cooler, drier air to the north.
On Friday, a historic, record-setting heat wave covered a sprawling region from the Midwest to the Southeast. All-time high temperatures records of 109 were established in Nashville and Columbia, South, Carolina and tied in Raleigh and Charlotte which hit 105 and 104. Here in Washington, D.C., the mercury climbed to an astonishing 104 degrees (breaking the previous record set in 1874 and 2011 by two degrees), our hottest June day in 142 years of records.
As this stifling air bubbled northward, clashing with the weather front draped from near Chicago to just north of D.C., thunderstorms erupted. They grew in coverage and intensity as they raced southeast, powered by the roaring upper level winds and fueled by the record-setting heat and oppressive humidity in their path.
The coverage and availability of this heat energy was vast, sustaining the storms on their 600 mile northwest to southeast traverse. The storms continually ingested the hot, humid air and expelled it in violent downdrafts - crashing into the ground at high speeds and spreading out, sometimes accelerating further.
Peak wind gusts in the D.C. region include the following:
71 mph near Dulles Airport
70 mph in Damascus, Md.
79 mph in Reston, Va.
65 mph in Rockville, Md.
70 mph at Reagan National Airport
76 mph in Seat Pleasant, Md. (Prince George’s co.)
77 mph in Swan Point, Md. (Charles co.)
70 mph in Ashburn, Va.
69 mph in Leesburg, Va.
In addition, an 80 mph gust was clocked in Fredericksburg. To the north and west, 91 mph and 72 mph gusts were measured in Ft. Wayne, Indiana and Columbus, Ohio.
This derecho event is likely to go down as not only one of the worst on record in Washington, D.C. but also along its entire path stretching back to northern Indiana.
As the intensity of the heat wave, without reservation, was a key factor in the destructiveness of this derecho event - it raises the question about the possible role of manmade climate warming (from elevated greenhouse concentrations). It’s a complicated, controversial question, but one that scientists will surely grapple with in case studies of this rare, extraordinary event.