Investigating the Impact of Volume Update Frequency on Distributions of Polarimetric Radar Variables Compared to High Resolution Hail Reports

The upgrade of the WSR-88D network to dual-polarization capabilities allows for further hail detection and sizing techniques, beyond reflectivity-only techniques, to be explored. The National Severe Storms Laboratory has developed a Hail Size Discrimination Algorithm (HSDA), based upon theoretical modeling, for use on S-band radars such as the WSR-88D. Evaluation of this algorithm has been ongoing using hail reports from the Severe Hazards Analysis and Verification Experiment (SHAVE), which collects reports of all hail sizes—including no hail—at a median spacing of approximately 2 km. A major source of ambiguity in the evaluation is due to the uncertainty of which radar volume to compare to the hail reports. Currently the maximum reflectivity within 2 km of the report at the lowest elevation is used to select the volume for matching. A recent upgrade to the WSR-88D, the Supplemental Adaptive Intra-volume Low-level Scan (SAILS), adds an additional 0.5 degree scan halfway through the radar volume when the radar is in VCP 12 or 212. This allows for data at the 0.5 degree scan to update every 2-3 minutes. SHAVE hail reports are compared to low level radar data using the maximum reflectivity within 2 km to match the scans. Distributions of radar variables are created using the SAILS data and then excluding SAILS data. The validity of the matching scheme and the impact on future algorithm development and evaluation are discussed.