During the afternoon and evening of Friday 29 June 2012, an intense, long-lived line of thunderstorms raced eastward at nearly 60 mph spanning an area from the Midwest to the Mid-Atlantic coast. In their wake, these storms left behind a swath of destruction that killed 22 people, caused millions in property damage, and caused massive power outages in major urban areas along the storm’s path. The term “derecho” is used to describe this organized system of violent and long-lived of intense thunderstorms. 

Essentially, a derecho is a long-lived, rapidly moving line of intense thunderstorms that produces widespread damaging winds in a nearly continuous swath. Because derechos are not common in our region, the term was relatively unknown to most residents here in the Mid-Atlantic prior to the June 29th event. Typically, the Mid-Atlantic averages one derecho once every 2 to 4 years. The last significant derecho to hit the Washington DC-Baltimore metro region was on June 4, 2008. 

This talk will review aspects of the 29 June 2012 derecho, 1) various observed meteorological data including radar and satellite imagery, 2) some pertinent meteorological conditions that created conditions favorable for the derecho that day, 3) real-time modeling of the derecho and 4) insights and challenges in both the forecast and warning of the derecho from the local National Weather Service/WFO-Sterling perspective.