A Comprehensive Analysis of Tornadic Debris Signatures Associated with Significant Tornadoes from 2010-2017

The tornado debris signature (TDS) is a highly correlated area in space and time of reflectivity greater than 30 dBZ, a strong radial velocity couplet, copolar correlation coefficient (ρ_hv) less than ~0.85, and differential reflectivity (Z_DR) of ~1.0 dB (Schultz et al., 2012, Van Den Broeke and Jauernic, 2014). TDSs have been shown to strongly correlate with debris lofted by tornadoes and with observed tornado damage tracks.

This study is an extension of Nelson and Banghoff (2015) and Nelson et al. (2018) and includes a more comprehensive analysis of radar characteristics of TDSs. All significant tornadoes observed within 150 km of a WSR-88D radar with dual-polarimetric capability across the continental U.S. from May 2010 to December 2017 (N=511) were studied. Given the presence of a TDS, several TDS variables were collected, including maxima in rotational velocity, azimuthal shear, TDS height and width, and minimum correlation coefficient. These variables were then compared to observed maximum wind speed estimates and path widths obtained from National Weather Service damage surveys via the Damage Assessment Toolkit (Camp et al., 2017). Using a combination of principal component analysis and multiple linear regression, a linear model was created between maximum TDS height, maximum azimuthal shear, and the maximum wind speed estimate, which yielded a strong multivariate correlation (r² = 0.71). When combined with percentile-based thresholds for discrimination between significant (EF2+) and violent (EF4+) tornadoes, the linear model could be used in the Impact-Based Warning (IBW) framework for tornado warnings issued by the National Weather Service.

Finally, the land cover types from the National Land Cover Database (2011) and subjective analyses of individual damage indicators from NWS damage surveys were obtained along the entire path for tornadoes with estimated maximum wind speed of at least 150 mph and path lengths greater than 15 km (N=20). The distribution of land cover types for each path are presented as well as the spatial-temporal correlations of the land cover types with the rotational velocity, TDS frequency, maximum TDS height and width, and minimum correlation coefficient values.