Inter-model Storm-scale Comparisons from the 2017 HWT Spring Forecasting Experiment

The 2016 and 2017 NOAA Hazardous Weather Testbed (HWT) Spring Forecasting Experiments (SFE) have featured the Community Leveraged Unified Ensemble (CLUE), a coordinated convection-allowing model (CAM) ensemble framework designed to provide empirical guidance for the development of operational CAM systems. The 2017 CLUE included 81 members that all used 3-km horizontal grid spacing, allowing direct comparison of forecasts generated using different dynamical cores, physics schemes, and initialization procedures. This study leverages the 2017 CLUE output to evaluate and compare the ability of various experimental and operational CAMs to realistically represent and predict thunderstorms. A major focus is identifying relative strengths and weaknesses of the ARW, NMM-B, and FV3 dynamical cores. The NSSL Multi-Radar/Multi-Sensor (MRMS) product suite is used to verify model forecasts and climatologies of observed variables. In the case of unobserved variables, the intermodel comparisons still prove useful for illuminating impacts of model design choices on storm prediction. Preliminary results from a wide range of grid- and object-based metrics – including vertical velocity and updraft helicity percentiles, mean storm motion, and composites of supercell reflectivity fields – reveal operationally important model differences that correlate with dynamical core or can otherwise be attributed to differences in model design (e.g., microphysics scheme). The outcomes of this and other CAM comparisons will be crucial for developing next-generation operational CAM systems.