Characterization of the 14 June 2011 Norman, Oklahoma, Downburst through Dual-Polarization Radar Observations and Hydrometeor Classification

Abstract

n 14 June 2011, thunderstorms developed along a cold front in central Oklahoma in a thermodynamic environment that was conducive for downbursts. One of the thunderstorms produced a wet downburst in Norman, Oklahoma, that resulted in surface winds in excess of 35 m s?1 (>80 mi h?1) and hailstones in excess of 4 cm in diameter. Unique 1-min observations of the downburst were recorded by an Oklahoma Mesonet station. These observations indicated a 6.6-hPa pressure rise that was coincident with a rain rate of 213 mm h?1 at the center of the downburst. In this event, both the research KOUN (Norman) and operational KTLX (Oklahoma City, Oklahoma) Weather Surveillance Radar-1988 Doppler (WSR-88D) instruments were scanning this downburst and its parent storm at close range (<30 km). KOUN provided polarimetric radar data (PRD) while both radars provided limited dual-Doppler coverage. The evolution of the downburst is analyzed mostly through the use of reconstructed range?height indicators of the PRD. A hydrometeor classification algorithm (HCA) is applied to the PRD to gain further understanding of the microphysical evolution of the downburst. Through the analyses, it is seen that graupel aloft made a transition to a nearly all rain and hail mixture above the 0°C level. This large area of mixed rain and hail eventually descended to the ground, causing the downburst. In this study, the HCA analyses are utilized to develop a conceptual model that characterizes the hydrometeor evolution of the parent downburst storm.