Total lightning signatures of thunderstorms and lightning jumps in hailfall nowcasting in the Beijing area

Based on total lightning location data from the Beijing Lightning Network (BLNET) and hailfall reports from 2015 to 2017 in Beijing, as well as S-band radar data from the Beijing Meteorological Observation Center, the total lightning activities for 148 hailfall events are analyzed with the identification method of strong convective cells (CCs) (similar to Thunderstorm Identification Tracking Analysis and Nowcasting, TITAN). Most of the hailstorms have a very high flash rate (FR), and a significant increase in FR is observed before hailfall events. The 2s lightning jump (LJ) algorithm (with 4 and 10 flashes/min activation thresholds for different districts of Beijing) is tested as a hailfall nowcasting predictor. The average LJ lead time is 27.1 min. LJs precede 81.8% of all hailfall events, and 38.6% of LJs are not followed by hailfall reports within one hour. The merging of two adjacent strong CCs usually forms hail-bearing severe thunderstorms producing a sudden increase in total lightning. In addition, most hailfall events occurred at the boundary of strong CCs instead of at the cell centers. This study shows that the total LJ is a potentially useful predictor for hail nowcasts in the Beijing area.