Application and Evaluation of WRF-HAILCAST hail size forecasts during NOAA/Hazardous Weather Testbed Spring Forecasting Experiments

The WRF-HAILCAST hail forecasting system is a one-dimensional hail growth model integrated into the WRF-ARW model designed to predict hail size at the ground.  During the past three NOAA Hazardous Weather Testbed Spring Forecasting Experiments (2014-2016), WRF-HAILCAST was run within the NSSL WRF-ARW and the CAPS Storm-Scale Ensemble Forecast (SSEF) system.  Subjective impressions of the experiment participants were recorded and will be shared.

Improvements were incorporated into WRF-HAILCAST between each of the three years, including adiabatic liquid water profiles, variable hail density for both wet and dry growth regimes, an updraft multiplier that parameterizes advection of the hail embryo across an updraft, temperature-dependent ice collection efficiency, physically realistic initial hail embryo sizes, and perturbations in insertion temperature of hail embryos.  Object-based and objective verification statistics will be presented from the WRF-HAILCAST forecasts from the NSSL WRF and CAPS SSEF ensemble from 2014-2016, as well as additional runs using the most updated version of the hail model.  Specific focus will be placed on the relative improvements seen between years, and how those are related to the physical improvements made in the WRF-HAILCAST model.