My research focused on derechos, more specifically progressive derechos, which are severe mesoscale convective systems (MCSs) that often form in benign synoptic conditions and have a characteristic bowing shape on radar (such as the radar image of the 29 – 30 June 2012 derecho located at the bottom of the page). Because derechos are high-impact weather events causing large swaths of wind damage, it is important to identify the corridors of the United States most favorable for their formation and to characterize the range of synoptic environments in which they form.

Above is a warm season (May – August), 18-year (1996 – 2013) climatology of progressive derechos east of the Rocky Mountains. The domain of interest was divided into 100 x 100 km grid boxes and Storm Prediction Center severe wind reports associated with each of the 254 identified derechos were counted. The color fill indicates how many derechos passed through a given grid box over the 18-year span. A prominent corridor of derecho activity exists from southeastern Minnesota to the Appalachian mountains in West Virginia where long stretches of instability and vertical wind shear sufficient to maintain MCSs most often set up in the warm season.

After we identified the derechos, Dr. Bosart and I examined synoptic maps at various atmospheric levels valid closest to each derecho initiation time in order to subjectively group the events into distinct synoptic categories. Above is a map of derecho tracks for one of the seven categories we created. In a northwest flow set-up, a northwest to southeast oriented upper-level jet is collocated with an axis of high low-level moisture and steep midlevel lapse rates, which produces the instability and vertical wind shear necessary for derecho formation and maintenance.

Above is a radar continuity map showing reflectivity every 2 hours for the 29 – 30 June 2012 derecho. This event is a member of the northwest flow category and was responsible for knocking out 60 percent of the power in West Virginia and causing over one billion dollars in damage along its path from northern Illinois to the Mid-Atlantic coast. Extreme instability both west and east of the Appalachians allowed this event to cross the mountains and become one of the strongest derechos on record.