NWC REU 2004
May 24 - July 31



Observations of the Zdr Column During Two Severe Weather Events

Cynthia Whittier, Don Burgess, Kevin Scharfenberg, and Paul Schlatter



The Zdr column was studied using data collected by the KOUN prototype polarimetric WSR-88D on 8 May and 9-10 May 2003 severe weather events. Eight storms 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 significant. The width of the Zdr column also varied from storm-to-storm, with the widest column nearly 6.3 km across and while the narrowest was 2.2 km across. When a bounded weak echo region was present, the Zdr column was usually colocated 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. It was found that the appearance of the Zdr column preceded the first warning by 15 minutes and the first severe weather report by 39 minutes.

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