Modeling the Distribution of Lightning Strike Distances Outside a Preexisting Lightning Area

The 45th Weather Squadron (45 WS) lightning warning process currently consists of 10 warning circles with a radius of 5 or 6 nautical miles (NM) depending on if one or several facilities are being covered, respectively. This 5 NM standard was established by the Air Force Instruction 91-203 (AFI 91-203). Due to the amount of lightning activity on the central eastern coast of Florida and the nature of the missions the 45 WS supports, the 45 WS actually assisted in the original development of this 5 NM criteria. Previous research that helped solidify this 5 NM safety distance concentrated on the distance of a lightning strike from the center of a lightning area and often suggested employing an even greater safety distance such as 10 NM. This discrepancy in the safe distance criteria prompted weather experts from the 45 WS to examine the methodology of past research and compare it to the way in which current lightning watches and warnings are issued. The result of this analysis revealed a discrepancy between the procedure of issuing lightning watches and warnings and the study methodologies. The difference experts found was that lightning watches and warnings are issued based on the distance from the edge of a lightning storm or area whereas the studies were considering the distance from the center of a storm. This distinction implied that the previous studies included extra distance in calculating the stand-off distance as the area from the center of a storm to the edge of the storm typically ranges from 3 to 7 NM. This knowledge prompted the commissioning of this study that looks at the distance of lightning strikes from the edge of a preexisting area.

The primary objective of this study is to determine the appropriate stand-off distance from the edge of a preexisting lightning area for the desired level of safety. The overall process through which this is accomplished relies on using processed Lightning Detection and Ranging (LDAR) data to map the movement of preexisting lightning storms using ellipses which will be updated with every lightning flash. A systematic recording ensues for the distance from the ellipse boundary of each flash occurring outside the ellipse. All of those exterior flash distances are then used to find the best-fit distribution from which the stand-off distance for the desired level of safety can be calculated.