Investigation of the Impact of Convection-Allowing Ensemble Size for Severe Weather Forecasting

During the 2016 NOAA Hazardous Weather Testbed (HWT) Spring Forecasting Experiment (SFE), a group of similarly configured convection-allowing models (CAMs) were contributed by community collaborators to comprise the Community-Leveraged Unified Ensemble (CLUE).  The CLUE was designed to allow for controlled experiments in testing various aspects of convection-allowing ensemble design.  One of the CLUE experiments examined during the 2016 HWT SFE was the impact of ensemble size, which involved comparing mixed-core ensembles with equal contributions of NMMB and ARW members of 6, 10, and 20 total members.  Early evaluation results from the 2016 HWT SFE revealed that the size of ensemble did not appear to have a substantial impact on the forecast quality of the probabilistic severe weather fields examined that utilized a 40-km neighborhood approach.  Based on these initial results, the effect of further reducing the ensemble size will be explored along with the impact of the neighborhood size used in probability generation and verification.