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ABSTRACT
The National Severe Storms Laboratory (NSSL) has developed and tested a tornado detection algorithm (NSSL TDA) that has been designed to identify the locally intense vortices associated with tornadoes using the WSR88D base velocity data. The NSSL TDA is an improvement over the current Weather Surveillance Radar-1988 Doppler (WSR-88D) Tornadic Vortex Signature Algorithm (88D TVS). The NSSL TDA has been designed to address 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%, FAR 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, and 2) not requiring the presence of an algorithm-identified mesocyclone. This manuscript discusses the differences between the NSSL TDA and the 88D TVS and presents a performance comparison between the two algorithms. Strengths and weaknesses of the NSSL TDA and NSSL's future work related to tornado identification using Doppler radar are also discussed.
1. Introduction
The capability to effectively warn the public and aviation community of severe and hazardous weather is a crucial mission of the National Weather Service (NWS) and the Federal Aviation Administration (FAA). It is imperative to both the NWS and FAA that such weather phenomena such as large hail, damaging winds, tornadoes, lightning, and flash floods be anticipated and identified. Many tools have been developed and implemented to help anticipate and diagnose these weather phenomena. One such tool is the Weather Surveillance Radar-1988 Doppler (WSR-88D) (Klazura and Imy 1993; Crum and Alberty 1993). This relatively new tool has enabled NWS forecasters to better anticipate and identify severe and hazardous events. It has been reported that the use of the WSR-88D has improved the timeliness and accuracy of severe thunderstorm and tornado warnings (Polger et al. 1994; Bieringer and Ray 1996). In recent years, a significant rise in the probability of detection (POD) as...