Observations of Upward Lightning-Producing Storm in Oklahoma

An upward lightning (UL) flash at a tall structure initiates due to a locally strong electric field without any nearby preceding discharge activities (self-initiated, SIUL) or after an in-cloud branching of a parent cloud-to-ground (CG) or intracloud (IC) lightning flash (lightning-triggered, LTUL). UL is usually associated with stratiform precipitation. It is not the most common type of CG lightning flash although it can be considered a threat to towers, tall buildings, and windmills. On 22 October 2017, 39 UL flashes were recorded by high-speed video cameras in Oklahoma City, OK in less than two hours after a leading-line trailing-stratiform squall line system passed over a region within twenty tall towers ranging in height from 100 m to 500 m. Within this context, we present an analysis of the SIUL and LTUL discharges quantified by using a combination of data from the Oklahoma Lightning Mapping Array (OKLMA), the operational KTLX Polarimetric Weather Surveillance Radar-1988 Doppler (WSR-88D) and the National Lightning Detection Network (NLDN). A series of vertical cross sections aligned with the horizontally extensive mapped lightning channels provided detailed visualization into the channel propagation paths relative to each polarimetric radar variable. Furthermore, the channel polarity and vertical charge structure were inferred from the OKLMA observations for accumulated periods near the time of the UL via manual flash by flash analysis and by the time-distance-altitude projection method of inferring velocity of lightning channels. A summary of the conditions that lead to the development of the phenomenon with respect to the storm evolution is provided and applications to the predictability of UL are discussed.