An Observational Analysis of Potential Terrain Influences on Tornado Behavior
In this presentation, we establish four repeatedly-observed behavioral modes that tornadoes appear to exhibit in the presence of terrain using a data set consisting of 72 cases. These four modes include: 1) formation/intensification on downslopes and dissipation/weakening on upslopes, 2) formation/strengthening on a plateau upslope/edge and weakening/dissipation on a plateau downslope/edge, 3) following a valley, and 4) following the edge of a plateau. Many of the 72 cases analyzed exhibit behaviors fitting multiple modes. In compiling these events, we analyze numerous sources of data, including multiple operational and research radars, National Weather Service and other ground and aerial surveys, and satellite data, to trace specific tornado tracks and to analyze changes in larger-scale storm characteristics, such as rotational characteristics of parent mesocyclones or mesovortices. Select case studies are utilized to illustrate examples of each interaction mode. The identification of these four potential terrain influence modes on tornado behavior will serve as a baseline for hypotheses leading to future observational, theoretical, and numerical modeling studies of severe storm interactions with terrain.