Radar observations of a negative cloud-to-ground storm 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 find a relationship between the microphysics and dynamics of severe storms on the High Plains and their unique positive cloud-to-ground (CG) lightning production. This study presents observations of a severe negative CG storm observed during the STEPS field campaign and compares it with the previously analyzed 29 June 2000 positive CG storm.

On 19 June 2000, a cell embedded in a convective complex produced abundant IC lightning but only a few CG strikes, which were predominantly of negative polarity. Surface winds of up to 33 m s^-1 and pea-sized hail were documented by surface observations. The storm developed southwest of the CSU-CHILL radar around 2300 UTC and traveled east-northeast over the CSU-CHILL radar and through the STEPS domain. It dissipated northeast of Goodland, KS just after 0200 UTC (20 June).

Two hours of dual-Doppler wind synthesis were analyzed to estimate the evolution of the three-dimensional wind field of this storm. Bulk hydrometeor types were objectively determined using the multi-parameter variables available on 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 this storm will be presented and compared with that of 29 June 2000.