The Spectrum of Progressive Derecho Formation Environments East of the Rockies

Progressive derechos are severe mesoscale convective systems that often form during the warm season (May–August) in benign synoptic environments east of the Rocky Mountains and cause, by definition, straight-line wind damage along paths upwards of 400 km long. This presentation will expand upon existing derecho climatologies with a warm season, 1996–2013 progressive derecho climatology highlighting spatial and temporal frequencies of progressive derechos over the 18-year span.

The presentation will also include results from the application of a subjective, seven-category classification scheme for progressive derecho synoptic initiation environments including derecho-relative composites of fields pertinent to progressive derecho formation. Results show corridors of enhanced atmospheric moisture, midlevel lapse rates, and vertical wind shear characterize derecho synoptic environments regardless of composite category.

Finally, case studies will be presented of two progressive derechos on opposite ends of the progressive derecho formation spectrum, one forming on the evening of 12 June 2013 ahead of a well defined upper-level trough and surface cyclone, and the other along a weak, east-west oriented surface boundary on the morning of 29 June 2012 in the absence of substantial large-scale forcing for ascent. Maintenance and demise of the two derechos will be linked to the distinct synoptic classes they represent.