THE USE OF VOLUMETRIC RADAR REFLECTIVITY PREDICTORS IN THE DEVELOPMENT OF A 2ND-GENERATION SEVERE WEATHER POTENTIAL ALGORITHM

The operational WSR-88D Severe Weather Potential (SWP) algorithm is an automated nowcasting procedure aimed at providing guidance in the det ection of severe local storms. It yields a numerical index proportiona l to the probability that an individual storm cell is producing, or wi ll shortly produce, large hail, damaging surface winds, or tornadoes. Currently, the SWP algorithm consists of a statistically derived funct ion 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 v olumetric reflectivity observations. Experimental second-generation SW P equations incorporating these new predictors were evaluated and thei r skill was compared to that of the operational SWP algorithm. Those p redictors that parameterize the magnitude of the reflectivity in the m iddle and upper portions of convective storms were found to have the m ost diagnostic information with respect to severe weather. Some of the se predictors rely only on reflectivity above 15 000 ft (4572 m) and t hus could be applied to storms beyond the current algorithm's range of 230 km. The skill of the second-generation equations within 230 km wa s found to be comparable to that of the current algorithm.