Lightning mapping observations in the western Great Plains

Observations have been obtained of the total lightning activity in western Great Plains storms using a GPS-based 3-D lightning mapping system. The observations were made in central Oklahoma in 1998 and during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) in northwestern Kansas during the summer of 2000. A tornadic storm observed on June 29 during STEPS exhibited a large `hole' or lightning-free region in the vicinity of an F1 tornado. The observations which show this are presented in the accompanying figure. Similar lightning-free regions were observed in the early stage of a tornadic Oklahoma storm and in a large Oklahoma supercell storm; they appear to be associated with strong updrafts in the storms. A number of storms have been observed during STEPS that produced predominantly positive cloud-to-ground (+CG) lightning, as opposed to the negative polarity CG discharges of most storms. The intracloud (IC) lightning in these storms was also inverted from normal polarity. The tornadic storm of June 29 produced inverted-polarity IC discharges, initially without any CG activity but then with significant numbers of +CG discharges beginning when the storm became tornadic. These and other features of the lightning activity in large storms may provide a useful diagnostic of storm type and severity.