Tools to Improve Tornado Warning Performance for Supercells: ZDR/KDP Separation and Size-Sorting Signals

Previous work investigated the possibility of utilizing certain dual-polarization radar fields (Z_DR and K_DP) to help discriminate between tornadic and non-tornadic storms. The main strategy was to infer trends in near-storm environmental vertical wind shear by evaluating the resulting raindrop size sorting. Later research demonstrated, via idealized numerical simulations, that hydrometeor size sorting is not fundamental to wind shear, but rather to the storm-relative flow itself. However, it was also noted that, particularly in supercell environments, storm-relative flow (using the degree of drop size sorting as a proxy) and lower tropospheric storm-relative helicity (SRH) are likely well correlated. As such, in supercell environments, it is hypothesized that patterns of Z_DR and K_DP can identify important trends in storm-relative flow and SRH, thereby helping to diagnose a storm’s tornadic potential.

To further build on earlier studies and test the hypotheses outlined above, a number of supercell storms (both tornadic and non-tornadic) across geographically diverse regions of the United States were evaluated. Newly developed analysis tools and visualization techniques were used to quantify the separation between Z_DR areal maxima in the Z_DR arc region and K_DP areal maxima within the K_DP foot. These radar signatures, when compared to mean storm motions, were then used to infer highly localized modulations of storm-relative flow and SRH over time.

Ongoing efforts to incorporate the outlined research results into National Weather Service (NWS) tornado warning operations, including those specifically undertaken as part of the NWS Central Region Tornado Warning Improvement Project (TWIP), will be discussed, along with future work.