Use of ZDR columns for early detection of severe convection within the operational radar network of the United Kingdom

Abstract

Differential reflectivity ($Z_{\mathrm{DR}}$) columns were observed using a Met Office three-dimensional radar composite. An algorithm for automatic detection of $Z_{\mathrm{DR}}$ columns was developed, based on $Z_{\mathrm{DR}}\ge 1.0$ dB and $Z_H\ge 10$ dBZ. Across three case days, detected $Z_{\mathrm{DR}}$ columns were found to precede severe convection in tracked convective cells with a range of lead times from 0 to 20 min depending on the case day. Requiring maxima above 1.4 dB and 30 dBZ of $Z_{\mathrm{DR}}$ and $Z_H$ respectively was an appropriate second condition for all three cases although the skill in the early detection of severe convection varied across case days. Despite the high probability of detections, the high false alarm rate accompanied by low critical success index and data latency limit performance based on the three cases considered in this study. Nevertheless, the ability to detect $Z_{\mathrm{DR}}$ columns in operational radar data with a useful lead time prior to severe convection in certain conditions is a promising development towards advancing nowcasting of severe convection in the United Kingdom.