11B.1 Using Polarimetric Radar Data to Identify Potentially Hazardous Hail Accumulations

Thursday, 11 January 2018: 10:30 AM
Room 17B (ACC) (Austin, Texas)
Aaron Ward, NWSFO, Amarillo, TX; and M. Kumjian, M. J. Bunkers, S. W. Bieda III, and R. J. Simpson

Some of the most dangerous and destructive thunderstorms are those that produce hazardous hail accumulations (HHA). For the purpose of this study, HHA storms are defined by hail accumulations of ½” or greater completely covering the ground. HHA storms almost always result in slick and hazardous road conditions, may result in flash flooding owing to clogged drainages and, at times, produce dense fog. There have even been at least two documented HHA cases that have directly resulted in fatalities due to hypothermia. Unfortunately, although the aftermath of these events garners wide media coverage, they have been challenging to forecast, and research into their evolution has been limited. However, current studies show that there may be some predictors for these events in an operational setting using dual-polarization radar signatures. These radar signatures, along with emerging environmental research, should help forecasters better communicate the risks associated with HHA storms.

This study focuses on the WSR-88D dual-pol radar signatures of HHA storms and shows how they can be used operationally to provide public awareness of HHA events in real-time. It is shown that low-level radar scans (< 2000 m AGL) which include anomalously large specific differential phase (KDP > 8 deg km-1), large reflectivity factor (> 65 dBz), and anomalously large differential attenuation, can be attributed to high concentrations of small melting hail. Ten HHA cases have been analyzed, and these dual-pol signatures are very recognizable. Moreover, these data can be used in an operational setting to better communicate the threat associated with a given thunderstorm. Analysis of these dual-pol signatures will be presented, and the operational implications will be further explored.

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