You Say ‘Derecho,’ We Say ‘Must-See’ Video
The cluster of severe thunderstorms that paralyzed the nation's capital for days beginning on June 29 originated in the Midwest. Fed by record warm surface temperatures, as well as a stationary boundary between hot and humid air to the south and cooler and drier air to the north, along with strong winds in the upper atmosphere, the storms organized into a bow shape, charging forward at speeds of near 60 mph. The storms produced widespread wind damage, with winds of 60-90 mph recorded from Illinois all the way to Virginia. The winds knocked out power to millions of people, causing the largest non-hurricane-related power outage in Virginia's history, and forced Mid-Atlantic residents to endure a record-breaking heat wave without the benefit of air conditioning.
Meteorologists, who can be rather fond of complicated terminology (“El Nino-Southern Oscillation,” anyone?) refer to this type of storm event as a derecho (pronounced de-RAY-cho), which is Spanish for “straight ahead.” This name is derived from the straight-line winds that characterize these events.
In the wake of the storms, there have been several thorough analyses published on the many factors that went into producing them. The Washington Post's Capital Weather Gang blog discussed the off-the-charts instability readings from June 29, and the role that global warming may have played by contributing to the record heat. Bob Henson of the University Corporation for Atmospheric Research discussed the history of derechos, and how this one stands up against the major events of the past. He also detailed how new computer models correctly forecast the event several hours in advance.
The geekiest dissection of the event comes from the University of Wisconsin's CIMSS Satellite blog. While the blog post itself is not exactly geared toward the weather novice, it features the incredible video below showing how the storms intensified as they plowed towards the Washington, D.C. area, taking advantage of the record heat and winds in the upper atmosphere that were conducive to severe weather. The deep, dark red hues show the coldest, highest cloud tops, which signify the strongest thunderstorm cells.