Comparison of Doppler Radar Correlation Coefficient, Spectrum Width, and Normalized Rotation in Areas of Rotational Circulations and Convergence Boundaries to Observed Convective Phenomena

National Weather Service (NWS) meteorologists evaluate various Doppler radar parameters and trends to make informed severe weather warning decisions to meet its core mission of protecting life and property. Meteorologists use reflectivity and velocity data most frequently, although spectrum width (SW), normalized rotation (NROT) and correlation coefficient (CC) show promise in their abilities to detect rotational circulations and convergence boundaries within supercells and quasi-linear convective systems (QLCSs). Studies show that low CC values co-located with strong low-level circulations in supercells are representative of a tornado on the ground. However, the mesovorticies associated with QLCSs are often weaker, smaller, shallower, and faster movers than their supercellular conterparts. As a result, it is difficult to discern a tornado debris signature (TDS) using traditional methods. Therefore, this study will examine radar data from past tornadic events to determine whether or not a combination of CC, SW, and NROT can successfully predict or identify tornadoes on radar.

A large sample of Doppler radar data from supercell and QLCS tornadic events in the Ohio and Mississippi River Valleys from 2008—2014 were collected and examined. Maximum values of SW and NROT as well as their heights above ground and depth of signals were recorded for as many possible scans before, during, and after the documented tornadic events. Minimum CC values and depth of signal were recorded for as many radar scans as possible during and after the tornadoes. Statistical analysis on supercell and QLCS data was performed and results are discussed. Preliminary findings suggest that large values of SW and NROT coincident with strong rotation are accurate indicators of tornadic circulation and may offer some insight into the strength of the tornado.