Lightning and radar observations of two storms observed during STEPS

The Severe Thunderstorm Electrification and Precipitation Study (STEPS) took place between 17 May 2000 and 20 July 2000 in eastern Colorado and western Kansas. STEPS aims to identify relationships between microphysics, dynamics and storm electrification, and in particular, investigate positive cloud-to-ground (CG) lightning production. This study compares a severe positive CG storm to a storm that produced no CG flashes observed during the STEPS field campaign.

On 3 June, an isolated cell produced three-quarter inch hail and intra-cloud (IC) lightning, but no CGs. A tornadic supercell on 29 June 2000 developed and remained within the STEPS radar domain for over four hours. This storm, which has been described in previous work, produced copious large hail, profuse IC lightning, and >90% of its CG strikes delivered positive charge to ground.

Multiple-Doppler wind syntheses were performed to estimate the evolution of the three-dimensional wind field of each storm. Bulk hydrometeor types were objectively determined using the multi-parameter variables available from the NCAR S-Pol and CSU-CHILL radars. The Doppler-derived kinematic fields were then compared with the microphysical classifications to look for trends in the evolution of these variables. Relationships in the time series trends of updraft and vertical vorticity statistics, hydrometeor echo volumes, and lightning flash rates for these storms will be presented and compared.