Mergers in supercell environments. Part I: Conceptual models of mechanisms governing merger outcomes

Supercell mergers remain an outstanding problem in severe weather forecasting. Two major concerns are predicting the long-term outcome of a merger and evaluating the potential for tornadogenesis. Through the use of numerical simulations, a large suite of idealized mergers has been examined, from which a basic set of conceptual models for the merger process has emerged. These conceptual models relate the relative location of mergers (i.e., merger location relative to the original storm updraft) to long-term (>40 minute) outcomes. Dynamical processes relevant to various types of merger have been identified. These conceptual models are presented along with observations of real-world events from VORTEX2 that provide an opportunity to test their validity. The possibility of tornadogenesis with each type of merger will be considered in Part II.