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 optimizing CAM ensemble design. 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. The 3-km grid spacing also facilitates comparison to operational CAMs such as the NAM CONUS nest.

This study leverages the 2017 CLUE output to evaluate and compare the capability of various experimental and operational CAMs to realistically represent thunderstorms. A major focus is identifying relative strengths and weaknesses of the ARW, NMM-B, and FV3 dynamical cores. Our assessment is concerned not so much with the accuracy of forecast timing and locations of individual storms, but with the general realism of storms simulated by each model. We therefore focus on generating and comparing model and NSSL Multi-Radar/Multi-Sensor (MRMS) climatologies valid over the duration of the 2017 SFE. A feature-based approach is used to focus the analysis on critical thunderstorm properties such as size, motion, updraft helicity, rainfall, and diurnal cycle. Preliminary results from a wide range of metrics reveal operationally important model differences that correlate with dynamical core. The outcomes of this and other inter-CAM evaluation studies will be crucial for the development and optimization of future, operational CAM systems and associated ensembles.