Exploration of the NSSL Maximum Expected Size of Hail (MESH) Product for Verifying Experimental Hail Forecasts in the 2014 Spring Forecasting Experiment
One of the goals after the conclusion of the 2014 SFE was to explore gridded MESH fields as an alternative and comparison to traditional LSRs. To nearly mimic the procedure during the SFE using severe storm reports, “practically perfect” [PP] hindcasts (Brooks et al. 1998) for MESH were constructed by applying a two-dimensional Gaussian smoother to values above an appropriate threshold (e.g., 1 inch) within 25 miles (i.e. 40-km radius of influence [ROI]) of a 1-km x 1-km grid box. The probabilities from the full-period (20-hr) experimental hail forecasts for Day 1 were compared directly to those obtained from the MESH PP hindcast (i.e., 20-hourly maximum MESH) by calculating the fractions skill score (FSS; Schwartz et al. 2010). In addition, contingency table forecast verification metrics (e.g., CSI) were calculated based on a set probabilistic threshold (e.g., 5%). The value of using MESH as a verification dataset will be judged on both a visual assessment of PP areas against those created from LSRs as well as the scores obtained from the statistical forecast metrics.