Winter precipitation type classification with a polarimetric WSR-88D radar

In the Spring of 2002, the National Severe Storms Laboratory in Norman, OK upgraded the KOUN WSR-88D radar to include dual-polarization capabilities. Polarimetric radars provide a wide range of benefits to operational users, including better identification and removal of non-meteorological targets, thereby leading to an improvement in data quality, and improved classification of precipitation types. Because KOUN is to serve as a prototype for a future national network of polarimetric radars (an upgrade of the existing WSR-88D network, expected to begin in approximately 2009), data quality and precipitation product enhancements realized from the KOUN data will soon become available to aviation users on a national scale.

In this paper, we focus on the operational benefits of improved detection of precipitation type in winter storms. Since the Spring of 2002, polarimetric radar data have been collected in 15 winter weather events, thereby providing statistical information that allows us to now quantify the polarimetric characteristics of winter precipitation in Oklahoma. Radar reflectivity (Z), differential reflectivity (ZDR), specific differential phase (KDP), and correlation coefficient (rhohv) are used to characterize the polarimetric differences between regions of dry and wet snow, sleet, ice pellets, and freezing rain. Rain/snow transition lines and the polarimetric signatures of melting snow and low bright band regions are also investigated. We will also report on efforts to develop an automatic, polarimetric bright band detection algorithm that will aid in the identification of freezing level height in precipitation systems.