Implementation of CAM-HAILCAST in the Stand-Alone Regional FV3

HAILCAST is a state-of-the-science, physically-based, one-dimensional hail model designed to forecast hail size that is driven by vertical profiles of meteorological fields from a convection-allowing model (CAM). Maximum hail size over a prescribed period of time is output to the model history output file. HAILCAST has been implemented in a variety of WRF-based CAMS, including the NSSL-WRF ensemble and over a subset of the members in the Community Leveraged Unified Ensemble (CLUE). It has been validated since 2014 at the NOAA Hazardous Weather Testbed (HWT) Spring Forecasting Experiment. This feedback, both from objective scores and forecaster subjective evaluation, has resulted in updates to HAILCAST physics that have shown promise for the operational forecasting of severe hail. Here, we provide details of the first implementation and validation of HAILCAST in a CAM based on the next-generation Finite-Volume Cubed-Sphere (FV3) dynamical core – specifically, the Center for Analysis and Prediction of Storms (CAPS) Stand-Alone Regional (SAR) FV3 model (hereafter, CAPS SARFV3). The HAILCAST physics routine communicates with the FV3 NGGPS diagnostics module and the maximum hail diameter field is passed to the NCEP postprocessor for output to standard model history files. The 2019 Spring Forecasting Experiment provided a framework for preliminary validation against the MRMS Maximum Expected Size of Hail (MESH) product. As well, we will describe differences in the relationships between HAILCAST hail sizes and storm surrogate updraft helicity and maximum updraft velocity fields for the CAPS SARFV3 and NSSL-WRF. Ongoing work will continue to refine the implementation of HAILCAST within FV3-based modeling systems, allowing for easy implementation in a future operational CAM such as FV3-HRRR.