A Proposed Radar Strategy for the Prediction and Warning of Severe Hail Using Polarimetric Radar Data

Ground-truth observations play a crucial role in the issuance of National Weather Service (NWS) Severe Thunderstorm Warnings for severe hail. Many radar warning techniques for severe hail are created off of these ground-based observations, which are correlated to quantitative threshold values that were observed at the time of severe hail occurrence. With the inclusion of Polarimetric radar (PR) data into NWS warning operations, the sampling of hydrometeors in both the horizontal and vertical provides the opportunity to discern amongst different hydrometeor types in the mixed phase region of a thunderstorm updraft. Used in conjunction with an understanding of thunderstorm dynamics and the surrounding thermodynamic and kinematic environment, PR data can provide the ability to forecast the occurrence of severe hail at the ground early in the lifecycle of a thunderstorm. A proposed strategy and decision aid are introduced that outline a qualitative conceptual forecast approach to the issuance of Severe Thunderstorm Warnings for severe hail using PR data. Applications of this approach are provided for two thunderstorms that occurred during the 21 May 2013 severe weather event across the NWS Albany, New York county warning area.