One of the most intense lines of thunderstorms in recent memory struck the Washington, DC metro region on Friday night, June 29th, as well as many other Midwestern and Mid-Atlantic locations on its way from Illinois/Indiana to the east coast. This particular kind of fast-moving, long-lived, large and violent thunderstorm complex is known as a “derecho”, and it is much more common in the Midwest and Great Lakes than in the Mid-Atlantic. Although a “derecho” can produce similar destruction to that of tornadoes, the damage is typically directed in one direction along a relatively straight swath. National Weather Service statistics indicate that “derechos” occur about once every four years in the Mid-Atlantic coastal region, but up to once a year or so in parts of the Midwest. The conditions necessary for the development of a “derecho” generally include the following:
1) A jet streak where upper level winds zip along at high speeds 2) Northern boundary of a hot air mass
These conditions were indeed satisfied in the Midwest and Mid-Atlantic on Friday as there was a strong upper level jet streak just to the north of this region and extreme heat enveloped the entire region along with a boundary zone set up just north of here. Temperatures on Friday, in fact, reached all-time highs for the month of June in many locations including at Reagan National Airport in Washington, DC (104 degrees). Thunderstorms erupted during Friday afternoon near Chicago, IL and then grew in intensity and coverage as they raced southeastward, powered by very strong upper-level winds and fueled by the record-setting heat in their 600 mile path to the east coast. Peak wind gusts reported in the Washington, DC region included 71 mph at Dulles Airport in VA, 79 at Reston, VA, and 77 mph at Swan Point, MD (Charles County). Farther upstream, wind gusts of 91 mph were measured in Fort Wayne, Indiana. Lots of people are hoping the climatology holds here and we have to wait another 4 years to experience another one of these kinds of meteorological events.