United States, National Weather Service

In the late 1990's, a probability of severe hail equation (LPSH75) for diameter greater than or equal to 0.75 in. (1.9 cm) was developed for the Columbia South Carolina County Warning Area (CAE CWA) using a logistic regression methodology. This equation provided a 'VIL of the Day' which forecasters used operationally as an aid in the warning decision making process. In early 2010, National Weather Service (NWS) criterion for severe hail was changed to a diameter greater than or equal to 1.00 in. (2.5 cm). The purpose of this study was to develop new objective methods to estimate the probability of severe hail based on the revised NWS definition. In addition to a new probability of severe hail equation (LPSH100) for diameter greater than or equal to 1.00 in. (2.5 cm), two equations (LPSH0 and LPSH-20) were developed that relate the height of the 50dBZ core of a particular thunderstorm to the 0°C and -20°C levels to estimate the probability of severe hail. LPSH0 and LPSH-20 can be useful before convection develops and in conjunction with radar storm interrogation by providing an objective method to estimate the probability of severe hail in near real time. Local applications were developed to display the severe hail probability output to the forecasters in the Advanced Weather Interactive Processing System (AWIPS).

Technical Attachment

National Weather Service (NWS)