THE NATIONAL-SEVERE-STORMS-LABORATORY TORNADO DETECTION ALGORITHM

The National Severe Storms Laboratory (NSSL) has developed and tested a tornado detection algorithm (NSSL TDA) that has been designed to ide ntify the locally intense vortices associated with tornadoes using the WSR-88D base velocity data. The NSSL TDA is an improvement over the c urrent Weather Surveillance Radar-1988 Doppler (WSR-88D) Tornadic Vort ex Signature Algorithm (88D TVS). The NSSL TDA has been designed to ad dress the relatively low probability of detection (POD) of the 88D TVS algorithm without a high false alarm rate (FAR). Using an independent dataset consisting of 31 tornadoes, the NSSL TDA has a POD of 43%, FA R of 48%, critical success index (CSI) = 31%, and a Heidke skill score (HSS) of 46% compared to the 88D TVS, which has a POD of 3%, FAR of 0 %, CSI of 3%, and HSS of 0%. In contrast to the 88D TVS, the NSSL TDA identifies tornadic vortices by 1) searching for strong shear between velocity gates that are azimuthally adjacent and constant in range, an d 2) not requiring the presence of an algorithm-identified mesocyclone . This manuscript discusses the differences between the NSSL TDA and t he 88D TVS and presents a performance comparison between the two algor ithms. Strengths and weaknesses of the NSSL TDA and NSSL's future work related to tornado identification using Doppler radar are also discus sed.