Observations of two positive cloud-to-ground 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 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 positive CG storm observed on 22 June 2000 during the STEPS field campaign and compares it with the previously analyzed 29 June 2000 positive CG storm.

At approximately 2300 UTC on 22 June 2000, a cell at the southern end of an extensive MCS entered the western lobe of the STEPS radar network and was already producing predominantly positive CG lightning. Another cell just north of the CSU-CHILL radar merged with this storm between 0000 and 0030 UTC (23 June). By 0300 UTC, this storm had exited the eastern lobe of the radar network, but persisted on the southern end of a well-organized MCS. This storm produced hail up to 1 inch and surface winds near 30 m s^-1.

Dual-Doppler wind syntheses 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. LMA lightning data was analyzed to infer the gross charge structure of this storm. Relationships in the time series trends of updraft and vertical vorticity statistics, hydrometeor echo volumes, charge structure, and lightning flash rates for this storm will be presented and compared with that of 29 June 2000.