Evaluation of NWS Storm-Based Warnings using Gridded Products

In 2008, the National Weather Service began issuing storm-based polygon warnings instead of county warnings. Only one severe hail, wind, or tornado report is needed to verify an entire warning polygon. Few severe weather reports in the warning, and in turn for the storm which prompted the warning, makes it difficult to determine the spatial extent of severe weather for a particular storm. Since 2006, the Severe Hazards Analysis and Verification Experiment (SHAVE) has been collecting severe weather reports at temporal and spatial resolutions much higher than those available in Storm Data. The National Severe Storms Laboratory (NSSL) produces several severe weather products, such as reflectivities at different isotherms and estimated hail size, on a grid for the entire contiguous United States. These grids could provide for synthetic verification of severe weather especially for the spatial extent of severe weather. This study will investigate how well the grids perform in determining where severe hail fell by using high resolution SHAVE reports. Discussion for applications of such grids for warning verification and improvement will also be included.