Analysis of Polarimetric Tornado Debris Signatures Observed by WSR-88D Associated with Significant Tornadoes

Analysis of WSR-88D dual-polarimetric data associated significant tornadoes from May 2010 through May 2014 indicates that 118 of them exhibited a polarimetric tornado debris signature (TDS). The TDS, as described by the NWS Warning Decision Training Branch and Schultz et al., 2012, is a strongly correlated area in space and time of reflectivity > 30 dBZ, a strong velocity couplet, correlation coefficient (CC) < 0.85 and ZDR of around 1.0, and has been shown to strongly correlate with debris lofted by a tornado and with observed tornado damage tracks.

This study characterizes the location, depth, width, minimum CC, throughout the life cycle of the tornadoes with a confirmed TDS. A least squares regression fit between maximum rated wind speed of a tornado and maximum altitude of the corresponding TDS yielded a coefficient of determination (R-squared) of 0.63. Some outliers from the predicted value were studied with possible differences in land type, forward speed and mixed-layer CAPE noted. Regression fits between maximum rated tornado wind speed and minimum CC value and between maximum tornado path width and maximum TDS width, resulted in much lower correlations.

The relatively strong correlation between tornado intensity and TDS height has led to a recent change in guidance and policy on how forecasters respond to tornado threats in some NWS Offices.