An Analysis of QLCS Lightning Distribution for Public Safety

Lightning strikes during outdoor events represent an area of concern for public safety. Attendant risks from thunderstorms, such as winds, hail, and heavy rain, are often given adequate warning time, but lightning strikes are much more unpredictable. They can occur in areas far removed from severe warnings or even rain. The present study examines a specific type of storm system, classified as a Quasi-Linear Convective System (QLCS), a system common to the Midwest and Plains states during spring and summer months, to determine the lightning distribution within these storms. Case studies were limited to storms occurring in Iowa between 2019 and 2023, and lightning and radar data were plotted using GR2 Analyst radar software. Lightning data was analyzed in 30-minute periods centered around peak storm intensity, which was approximated using GR2’s volumetric analysis to find the highest dBZ (reflectivity) value at any level in the storm’s life cycle using roughly two-minute interval radar images. Based on the dBZ values in which the strikes occurred, they were placed into four categories: “QLCS,” (occurring in areas greater 40 dBZ) “Trailing Stratiform Region,” (behind the leading edge between 25 to 40 dBZ) “Trailing Non-Precipitation,” (behind the leading edge less than 25 dBZ) and “Leading Edge Strike.” (less than 40 dBZ in front of the storm). Using GR2’s “place marker” feature, the distance from the storm for strikes in the “Leading Edge” category was measured relative to the 40 dBZ contour along the storm motion vector. Preliminary results from eight cases show that 84.0% of strikes occur within the QLCS, 8.6% in the Trailing Stratiform region, 1.8% in Trailing Non-Precipitation regions, and 5.5% as Leading-Edge Strikes. Further examination of this data investigated the effectiveness of the NCAA lightning policy, finding it to be 97.9% effective at avoiding lightning strikes using a 6-mile threshold. It also examined the efficacy of other distance thresholds and the location of strikes falling outside NCAA policy. In the next month, two to four more cases will be analyzed, bringing the total number to ten to twelve.