S-Band Polarimetric Analysis of the 23 May 2011 Oklahoma Record Hailstorm Using High-Resolution Observations during HailSTONE

During the afternoon of 23 May 2011, several supercells developed along a dryline in west-central Oklahoma. One of these supercells became a prolific giant hail producer across rural areas of Washita, Kiowa, and Caddo Counties, and was sampled by HailSTONE (A Hail Spatial and Temporal Observing Network Effort) for 2 hours. Substantial ground truth of hail information was obtained by seven hail intercept vehicles, several which were capable of penetrating the hail core in real-time. Each project vehicle documented the specific geographic coordinates and time of the hail fall, noting the maximum and average diameter, circumference, and general concentration of the hail stones at numerous locations. Approximately 270 unique reports of hail were recorded by HailSTONE from this particular supercell, 106 of which were baseball-sized or larger (7+ cm; 2.75+ in.). In contrast, Storm Data contained only 11 reports of hail from the storm, with just 3 entries of baseball-sized or larger hail. Additionally, HailSTONE identified and measured a 15.24 cm (6 in.) stone near Gotebo, Oklahoma, which has since been certified as the new state record for hail diameter.

This research examines dual-polarization data from the Norman (KOUN) prototype radar synthesized with the high-resolution hail dataset collected by HailSTONE. This observational dataset allows for a meaningful validation of polarimetric S-band radar signatures associated with giant hail by representing the true hail-fall character of the storm and mitigating the traditional spatial and temporal limitations inherent to Storm Data. Polarimetric radar presentation of hail fall, a quantitative comparison of low-level polarimetric variables to hail sizes, and the utility of polarimetric signatures in forecasting hail size will be discussed. With the ongoing national upgrade of the Weather Surveillance Radar 1988 Doppler (WSR 88D) network to dual-polarization, this study seeks to further demonstrate the increased benefit polarimetric data provides to operational meteorology.