Impact of Increased Resolution on Storm-Scale Ensemble Performance in the US Southeast

The VORTEX-SE program aims to reduce loss of life and property from tornado damage. Amongst the challenges of risk communication and warning systems, there is evidence that increased resolution of a limited-area numerical weather prediction model will better represent the updraughts associated with tornadogenesis in the southeastern US. These may occur in both cellular and linear convective models. However, a threefold increase in grid resolution demands a ninefold increase in computational demand; as such, given a finite computational resource, the number of ensemble members must be balanced with grid spacing. This presentation details results comparing a 3-km ensemble to a 1-km ensemble, and its impact on skill and spread while simulating severe weather outbreaks. Evaluation is performed with a range of scoring techniques, reflecting the challenges of storm-scale verification, including object-based and scale-aware methods. We also address whether the majority of the ensemble envelope can be captured by a limited subset of ensemble members, which would free up computational power for use in resolution improvements.