The Use of Volumetric Radar Reflectivity Predictors in the Development of a Second-Generation Severe Weather Potential Algorithm

Abstract

The operational WSR-88D Severe Weather Potential (SWP) algorithm is an automated nowcasting procedure aimed at providing guidance in the detection of severe local storms. It yields a numerical index proportional to the probability that an individual storm cell is producing, or will shortly produce, large hail, damaging surface winds, or tornadoes. Currently, the SWP algorithm consists of a statistically derived function of the cell's maximum vertically integrated liquid and horizontal areal extent. In an attempt to refine the algorithm, a wide variety of new statistical predictors of severe weather have been derived from volumetric reflectivity observations. Experimental second-generation SWP equations incorporating these new predictors were evaluated and their skill was compared to that of the operational SWP algorithm. Those predictors that parameterize the magnitude of the reflectivity in the middle and upper portions of convective storms were found to have the most diagnostic information with respect to severe weather. Some of these predictors rely only on reflectivity above 15 000 ft (4572 m) and thus could be applied to storms beyond the current algorithm's range of 230 km. The skill of the second-generation equations within 230 km was found to be comparable to that of the current algorithm.