Sunday, 9 January 2005
Observations of the Zdr column during two severe weather events
The Zdr column signature was studied using data collected by KOUN, the prototype polarimetric WSR-88D at the National Severe Storms Laboratory in Norman, Oklahoma. Eight storms from two severe weather events during the Joint Polarization Experiment (JPOLE), 8 May 2003 and 9-10 May 2003, were chosen for detailed study. The height above the 0°C level, width, location, maximum values of Zdr within the column, and time of appearance were recorded for each of these storms. There were differences in the height of the Zdr column from storm-to-storm, but when beamwidth error was considered the differences were not identifiable. The width of the Zdr column also varied from storm-to-storm, with the widest column nearly 6.3 km across and the narrowest 2.2 km across. When a bounded weak echo region was present, the Zdr column was usually co-located with it. Zdr values within the column ranged from 0.9 dB to 5 dB. Comparisons were made between the time of the first Zdr column appearance and the first National Weather Service-issued severe thunderstorm warnings and severe weather reports. The appearance of the Zdr column preceded the first warning by an average of 15 minutes and the first severe weather report by an average of 39 minutes.