Dual-Polarization Radar Observations of an Enhanced Precipitation Hail and Flash Flood Event

Dual-polarization radar data including Correlation Coefficient, Differential Reflectivity, and Specific Differential Phase (KDP) have been used in warning operations at NWS Amarillo since November 2011. In contrast to conventional WSR-88D data which only indicates the relative size of hydrometeors, dual-polarization radar data samples hydrometeors in both the horizontal and vertical planes to enhance the forecaster's ability to interrogate size, shape, and variations of weather and non-weather targets.

Extreme values of KDP which ranged between 9.75 and 9.95 deg/km were sampled by the Amarillo, Texas WSR-88D during a rare meteorological event on 11 April 2012. These very high KDP values suggested high liquid content and mass quantities of water-coated small hail. During this event, hail glaciers up to 2 m in depth formed during a flash flood and intense hailfall as nearly 8 cm of rain fell along U.S. Highway 287 near the Canadian River.

A post-storm study revealed flares containing a total of 400 g of silver iodine had been deployed in and around the 11 April 2012 storm by the Panhandle Groundwater Conservation District 30 to 60 min before the extremely high values of KDP were observed. The goal of the Water District's operations was to enhance precipitation by cloud seeding non-severe thunderstorms to increase the number of hydrometer nuclei. Such precipitation enhancement is believed to increase the rainfall efficiency of cumuliform clouds by as much as 10 percent. This presentation will show the results of an investigation of the correlation between the extremely high values of KDP observed on 11 April 2012 and the weather modification activities.