Radar-Detected Mesocyclone Tilt in Tornadic and Nontornadic Supercells

While supercell thunderstorms are the storms with the greatest potential of producing tornadoes, the majority of supercells do not produce tornadoes. Recent work has demonstrated that low-level (LL) vertical wind shear and lifting condensation level (LCL) height in the storm inflow region are the most promising discriminators between tornadic and nontornadic supercells. It is anticipated that as the horizontal distance between the LL and mid-level (ML) mesocyclones (mesocyclone tilt) decreases, the likelihood and intensity of a tornado increase. It is expected that there is an orientation of both LL vertical shear and lower LCL height that results in a smaller mesocyclone tilt. This study builds a climatology of radar data to distinguish between tornadic and nontornadic supercells. Level-II and -III Weather Surveillance Radar-1988 Doppler data were collected and processed for a subset of isolated supercells in the contiguous United States from 2009 to 2015. From this initial climatology, LL and ML azimuthal wind shear maxima are located, representing the LL and ML mesocyclones, and the horizontal distance between each maximum is calculated during the evolution of each supercell. Results connecting the mesocyclone tilt to aspects of the near-storm environment, including LL shear magnitude and orientation and LCL height, will be discussed. Characteristics of the storm environment are obtained from proximity soundings derived from the Rapid Update Cycle and Rapid Refresh model analyses. Statistical and observational analyses of the climatology and of individual case studies will be presented Significantly tornadic supercells are associated with low LCL heights, strong southwesterly LL vertical wind shear, and critical angles below 100°. While smaller mesocyclone tilts are often associated with significant tornadoes, there is considerable overlap between distributions, suggesting that nontornadic and weakly tornadic storms may also have small tilts. There may be also a balance of shear orientation that moderates the position of outflow to result in a small positive or negative mesocyclone tilt. Further consideration should be given to the LL kinematic storm environment when discriminating between tornadic and nontornadic supercells