Analysis and Characterization of QLCS Tornadic Debris Signatures for Utilization in Operational Settings

Much research has been conducted to further understand and characterize tornadic debris signatures (TDS's). Generally, TDS's are characterized by values of horizontal reflectivity (ZHH) that are greater than 40 dBZ, correlation coefficient (ρHV) values that are less than 0.8 for S-band (0.7 for C-band), and near 0 dB differential reflectivity (ZDR). All of these values must be collocated with an area of rotation evident in the radial velocity (VR) data. Numerous researchers have set out to understand the correlation between TDS characteristics and tornado properties and environments such as: EF-scale rating, tornado path length, land cover, etc. Prior research has shown that TDS's that are associated with stronger tornadoes, particularly those created by supercells, exhibit an increased ease of detectability than TDS's associated with weaker tornadoes. As a result, there have been very few case studies that focus solely on debris signatures produced by lower EF-scale tornadoes.

For this study, the primary objective is to characterize TDS's that are associated with weaker tornadoes (EF-0, EF-1, and some low end EF-2's) that form in a Quasi-Linear Convective System (QLCS) environment. Characteristics of QLCS TDS's (e.g., size or areal extent, height, duration, etc.) are compared to supercell TDS's. By understanding the differences and similarities of TDS's in the two storm modes, researchers, forecasters, and warning coordination personnel will be able to improve the utility of TDS's in operational settings.

Data from the Advanced Radar for Meteorological and Operational Research, ARMOR (C-band), and several National Weather Service Weather Surveillance Radars - 1988 Doppler, WSR-88D's (S-band), were collected and utilized for this study. Numerous polarimetric variables were recorded for each TDS which include: ZHH, VR, ρHV, ZDR, and spectrum width (σ). The maximum and minimum values for each variable are recorded to investigate potential refinements to the TDS thresholds for operational forecasters to utilize in QLCS situations. Preliminary results show that the TDS's associated with QLCS tornadoes generally last one, but no more than two volume scans, and rarely are higher than a few thousand feet.