An Examination of Varying Supercell Environments Over The Complex Terrain Of The Eastern Tennessee River Valley

This study examines the similarities and differences between five events when supercells over the eastern Tennessee River Valley had either low or high tornado-producing efficiency. The three events with a high tornado-producing efficiency (defined in this study as an event where every supercell produced at least one tornado) were characterized by the tornado-producing supercells tracking near a well-defined, preexisting west-to-east oriented quasi-stationary frontal boundary. The other two events with a low tornado-producing efficiency had supercells that were located and moved farther away from a south-to-north oriented cold front. In the high tornado-producing efficiency events, the supercells likely encountered lower lifted condensation level (LCL) heights and higher helicity values for a longer distance along the west-to-oriented qausi-stationary frontal boundaries. In the low tornado-producing efficiency events, the supercells encountered higher LCL heights and lower helicity values as they propagated farther away from the south-to-north oriented cold fronts, especially across the Great Tennessee Valley where the lowering elevation from the Cumberland Plateau aided in the higher LCL heights. During the one non-tornado-producing event, the combination of high LCL heights, a lack of low-level directional wind shear, and the location of the supercell paths away from a well-defined surface boundary likely caused the lack of tornado development, despite the presence of numerous supercells. The two tornado outbreak events (defined in this study as an event that produced five or more tornadoes) experienced the strongest low-level helicity values, although the low-level instability values were the weakest. The higher low-level instability during the other three non-outbreak events may have compensated for the weaker, but still significant, low-level wind shear. Another common trait observed in four of the five events was the location of strong equivalent potential temperature advection at the surface near the locations of the observed supercells and tornadoes.