Severe mesoscale convective systems (MCSs), including derechos, are relatively common across the Upper Mississippi and Ohio Valleys of the U.S. in the summer months based on several climatological studies. However, these studies show the frequency east of the Appalachians, especially the southern Appalachians, drops off noticeably. These results are supported by forecaster observations at the NWS in Blacksburg, Virginia. In an attempt to better understand the controlling environmental parameters and mechanisms behind those few severe MCS events that maintain their organization and severity through the southern Appalachians versus the larger number that do not, we identified a number of candidate events since the mid 1990s (when the forecast office and upper air site were established in Blacksburg) to help make this distinction. We discarded events that lacked an organized structure observed on archived radar mosaics, events that were driven by a strong cold frontal system, and events where archived radar data were unavailable and severe weather reports alone were not sufficient to imply an MCS.

Using the remaining 10 events, we have attempted to separate them into two main categories: 1) severe weather continued east of the Appalachians (e.g. up to and beyond the Blue Ridge), or 2) severe weather dissipated as it reached the Appalachians. We then examined a number of parameters related to moisture, instability, shear and winds derived from modified soundings representative of the pre-storm environment at Blacksburg (the only upper air site in the southern Appalachians), and also looked at the synoptic patterns with these events to determine if there were any distinctions between the two categories.

Based on difficulty clearly separating a few of these events into an obvious category and the relatively low number of total events used, conclusions so far have to be considered preliminary. Any distinctions were subtle, and not very consistent from case to case, but we will highlight a few which appeared to be the most important and worthy of more thorough examination in future research. A brief comparison to an isolated, long-lived, severe supercell that passed through the southern Appalachians will also be made.