An Observational Investigation of Mesoscale Convective Systems Crossing the Appalachian Mountains

Mesoscale convective systems (MCSs) in the eastern portion of the United States present a unique forecasting problem due to the influence of the Appalachian Mountains. At times these systems are able to cross the terrain, often producing severe weather in the lee of the Appalachians. Other times, they instead dissipate upon entering the mountains. In order to address this problem, a sample of ten crossing and ten non-crossing cases were taken from the Keighton et al. (2007) database of MCSs in the Appalachian region from 2000-2005. General characteristics such as convective mode, forcing, orientation of the MCS compared to the mountains, time of day, and synoptic scale setting will be discussed. Additionally, observed soundings for each case were used to compute numerous kinematic and thermodynamic parameters. These soundings were separated into two categories: upstream, representing the environment west of the mountains, and downstream, corresponding to the environment east of the mountains. The downstream soundings are better able to distinguish between crossers and non-crossers, particularly via a few key instability and shear parameters. These observational results and our working hypotheses will be presented. Our long range goal is to differentiate between crossing and non-crossing environments.