How Well do ZDR Arc Metrics Indicate Potential for Strong Low-Level Rotation in Supercells?

Differential reflectivity (Z_DR) arcs are one of the most prominent dual-polarization features of supercell storms, and a strong, well-defined Z_DR arc is often cited as indicating potential for a supercell to develop strong low-level rotation and potentially become tornadic. Recent observational and theoretical work has posited that this is due to the correlation between environmental low-level shear and storm-relative helicity and the magnitude of size sorting by the storm-relative wind which creates the Z_DR arc signature. However, relatively little formal observational work has been done to quantify the relationship between time trends in Z_DR arc metrics and low-level rotation over supercell life cycles. In this study, time series of manually calculated Z_DR arc areal extent for a large sample of supercells are compared to time series of rotational velocity and Gibson Ridge Analyst 2 normalized rotation to determine how well trends in Z_DR arc extent foreshadow changes in low-level rotation magnitude. In addition, time series of maximum and mean Z_DR values in the arc obtained from an automatic Z_DR arc identification and tracking algorithm in Python developed for this project are compared to rotational velocity and normalized rotation time series to determine how changes in these Z_DR arc metrics relate to low-level rotation potential.