Manda Chasteen-December 8

An investigation of mesoscale processes and convective morphology on 27 April 2011

The 27 April 2011 Super Outbreak, which was part of a multi-day outbreak of severe weather spanning 25-28 April 2011, produced approximately 199 tornadoes, which resulted in 321 fatalities and more than 2700 injuries. The 27 April outbreak comprised three tornadic systems, with the supercell outbreak being the most notable for producing long-track, strong tornadoes. However, a morning QLCS was also especially severe, producing 76 tornadoes of up to EF3 intensity. Additionally, a second midday QLCS occurred over northern Mississippi and Alabama, which was responsible for the development of a thermal boundary. This boundary influenced the evolution of the northern supercells later during the day.

This goal of this study is to determine how meso-beta? scale dynamical processes resulted in the formation of these three systems and what environmental factors led to the differing organization, morphology, and severity of convection on 27 April. While several studies have examined the roles of surface boundaries in the initiation and organization of convection, limited studies have thoroughly investigated the roles of mesoscale forcing and organizational mechanisms for convection located within the warm sector (i.e., not along a surface boundary). Some potentially important phenomena for convective organization found in past studies are cold fronts aloft, mesoscale instabilities, and gravity waves generated both by convection and by the geostrophic adjustment process in response to unbalanced flow aloft. The role of such mesoscale processes may be heavily influenced by the environmental response to previous convection, which warrants a thorough investigation into the influence that earlier convection may have had on the eventual evolution of the supercell outbreak. A discussion of these potential processes and their hypothesized role in the evolution of this outbreak will be discussed in the context of proposed future work.