Investigation of a Severe Downburst Storm near Phoenix, Arizona, as Seen by a Mobile Doppler Radar and the KIWA WSR-88D

Abstract

A Shared Mobile Atmospheric Research and Teaching Radar (SMART-R) was deployed near Phoenix, Arizona, during the summer of 2004. The goal was to capture a severe microburst at close range to understand the low-altitude wind structure and evolution. During the evening of 27 July, a severe storm formed along the Estrella Mountains south of Phoenix and moved south of the SMART-R as well as the National Weather Service?s (NWS) Weather Surveillance Radar-1988 Doppler (WSR-88D) in Phoenix (KIWA). Several microburst?downburst pulses were observed by radar and a surface wind gust of 67 mi h?1 was reported. The radar data illustrate the finescale structure of the microburst pulses, with the SMART-R?s higher-resolution data showing Doppler velocities 3?4 m s?1 greater than the KIWA radar. SMART-R wind shear values were 2?3 times greater with the finer resolution of the SMART-R revealing smaller features in the surface outflow wind structure. Asymmetric outflow may have been a factor as well in the different divergence values. The evolution of the outflow was very rapid with the 5-min KIWA scan intervals being too course to sample the detailed evolution. The SMART-R scans were at 3?5-min intervals and also had difficulty resolving the event. The storm environment displayed characteristics of both moderate-to-high-reflectivity microbursts, typical of the high plains of Colorado.