Anticipating cloud-to-ground lightning initiation and frequency using WSR-88D reflectivity data

Cloud-to-ground (CG) lightning ranks as one of the most frequent, damaging, and deadly weather hazards in the United States, occurring in both “severe” and “non-severe” thunderstorms. Despite this, CG lightning is not included as a “severe weather” criterion. Real-time imminent threat information about CG lightning is not routinely provided to the public, perhaps due to the belief that lightning is unpredictable, and the sheer number of thunderstorms that produce lightning each year.

Based on smaller prior studies, a larger study was completed in 2006 at the NWS Jacksonville Florida forecast office, involving over 1,150 convective cells from over 20 different thunderstorm events across the southeastern United States. The study focused on radar clues suggesting the imminent onset of CG lightning, as well as the onset of numerous CG strikes. The study confirmed the results of previous studies, finding a probabilistic relationship between thunderstorm intensity, as suggested by the height of the 40dBZ echo in relation to the estimated environment -10°C isotherm height, and the initiation and frequency of CG lightning strikes. Furthermore, the results suggested that an average lead time of 5-15 minutes (1-3 radar volume scans) is achievable. Based on the results, real-time probabilistic guidance can be generated, leading to real-time lightning threat information not only for CG strike initiation, but also for CG strike frequency and perhaps even cessation.

This poster will provide the results of the study, which demonstrated: (1) very low probabilities for CG lightning while the 40dBZ echo remains below the theoretical updraft core -6°C isotherm height (which approximates the environment -10°C isotherm height in a moderately unstable air mass); (2) a sharp increase in the probability of CG lightning as the 40dBZ core exceeds the updraft core -6°C isotherm height; and (3) a sharp increase in frequent-strike probabilities as the 40dBZ core extends at least 3km above this height. The results also showed an average 5-15 minute (1-3 radar scan) lead time prior to CG lightning (or frequent-strike) initiation. The poster will also include several case examples demonstrating the potential utility of real-time, cell-based CG lightning probabilities that can be developed for online display.