Exploring the developmental milestones of supercell thunderstorms from convection initiation through maturity

The initiation of supercell thunderstorms presents a forecasting challenge due to the complexities of the interaction between growing cumulus clouds and wind shear. Previous research on convection initiation has largely focused on identifying the processes and environmental characteristics that control when and where long-lived thunderstorms will develop. However, once a persistent thunderstorm updraft does form in a sheared environment, several “milestones” of supercell evolution – including updraft splitting and cold pool formation – often must occur before the onset of severe weather hazards. Therefore, a better understanding of these developmental milestones may provide useful information for the forecasting of both convection initiation and supercell hazards.

The goal of this research is to document early supercell evolution in a variety of environments. To address this goal, a matrix of CM1 simulations (dx = 100 m) with variable environmental thermodynamic and kinematic profiles was developed and analyzed. Preliminary results from these simulations indicate that there is large variability in early supercell evolution as a function of the environment. First, the timing of updraft splitting is sensitive to environmental stability. Updrafts split faster in environments with greater low-level stability, suggesting an important role of wake entrainment processes in eroding the center of the incipient updraft. Second, cold pool development is sensitive to both environmental stability and hodograph curvature. Most notably, in relatively stable environments characterized by strongly curved hodographs, the incipient updraft overruns the developing cold pool, resulting in a poorly-organized supercell by the end of the simulation. Finally, sensitivity tests with different microphysics schemes indicate that the simulated early supercell evolution is strongly dependent on the microphysics scheme used. Given that characteristics of early supercell evolution can vary markedly as a function of the storm environment and microphysics, additional field observations in this period of storm evolution may be particularly beneficial.