Comprehensive Analysis and Regional and Seasonal Differences of Tornado Debris Signatures Associated with Significant Tornadoes from 2010-2017

The tornado debris signature (TDS), as described by the NWS Warning Decision Training Branch, (Schultz et al., 2012, and Van Den Broeke and Jauernic, 2014) is a highly correlated area in space and time of reflectivity > 25-30 dBZ, a strong velocity couplet, correlation coefficient < 0.85-0.90, and differential reflectivity () of around 1.0. A TDS has been shown to strongly correlate with debris lofted by a tornado and with observed tornado damage tracks. What composes the non-meteorological “debris” is not clear, but is theorized to be mostly comprised of small, easily-lofted vegetation such as leaves.

This study is an extension of Nelson and Banghoff (2015) and Nelson et al. (2018) and includes a more comprehensive analysis of trends and regional and seasonal differences of the TDS. 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=515) were studied. The prevalence of a TDS, the maximum height and width of the TDS, and the minimum correlation coefficient of a TDS were compared with the maximum rotational velocity and observed maximum wind speed estimates and path widths obtained from NWS damage surveys via the Damage Assessment Toolkit (Camp et al., 2017). These results were then stratified by broad vegetation areas of the country and during the different seasons, corresponding to different stages of deciduous trees and agriculture growth. For instance, between the abscission period when deciduous trees lose their leaves and the dormant stage, leaves may more easily become lofted during a tornado and more likely to be detected by dual-polarimetric radar.

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 150 mph or greater and path lengths greater than 15 km (N~20). The distribution of land cover types for each path will be presented as well as the spatial-temporal correlations of the land cover types with the rotational velocity, TDS prevalence, maximum height and width and minimum correlation coefficient values.