Rapid-Scan Radar Observations of Zdr Column Depth and Its Potential Use During the Warning Decision Process

National Weather Service (NWS) forecasters use a variety of tools and apply scientific conceptual models during the warning decision process to anticipate changes in storm intensity. The dual-polarization upgrade to the national WSR-88D network has provided new opportunities for forecasters to identify and examine signatures (such as Z_DR columns) that were previously unavailable to them. Since Z_DR columns may provide important information to forecasters about a storm’s intensity, a research dual-polarization WSR-88D located in Norman, Oklahoma (KOUN) was used to sample the Z_DR columns of 47 different storms. Specialized 90° sector scans and custom volume coverage patterns allowed for volume update times of two minutes or less, which provides a unique opportunity to study Z_DR column evolution and the impacts of radar-update time on observing Z_DR columns.

The purpose of this study is to analyze Z_DR column depth, -20C reflectivity core, and mesocyclone evolution together across multiple storm modes (e.g., supercells, multicells) to provide a means for integrating Z_DR columns into existing forecaster conceptual models. Time series plots were created to qualitatively analyze any relationships between Z_DR columns, storm reports, and signatures commonly used by forecasters during the warning decision process (e.g., mesocyclones). Statistical relationships were also examined to quantify any operationally relevant connections between each signature. Z_DR columns do appear to offer additional insight into storm intensity and hailfall at the surface. The lead author will discuss key findings of this ongoing study.