Comparing Polarimetric Signatures of Proximate Pretornadic and Nontornadic Supercells in Similar Environments

Abstract

Abstract While prior research has shown that characteristics of the supercell environment can indicate the likelihood of tornadogenesis, it is common for tornadic and nontornadic supercells to coexist in seemingly similar environments. Thus, some small-scale factors must support tornadogenesis in some supercells and not in others. In this study we examined polarimetric radar signatures of proximate pretornadic and nontornadic supercells in seemingly similar environments to determine if these radar signatures can indicate which proximate supercells are pretornadic and which are nontornadic. We gathered a collection of proximity supercell groups and developed a method to quantify environmental similarity between storms. Using this method, we selected pretornadic–nontornadic supercell pairs in close proximity in space and time having the most similar environments. These pairs were run through an automated tracking algorithm that quantifies polarimetric signatures in each supercell. Supercells with larger differential reflectivity (ZDR) column areas were more likely to become tornadic within the next 30 min compared to neighboring supercells with smaller ZDR column areas. In about two-thirds of pairs, the pretornadic supercell had a larger ZDR column area than the nontornadic supercell prior to its maximum low-level rotation, which is consistent with much prior work. The ZDR arcs could not discriminate between pretornadic and nontornadic supercells, and hailfall area was larger in pretornadic supercells. The separation distance between the specific differential phase (KDP) foot and the ZDR arc was larger in pretornadic supercells, yet was a limited result due to the small sample size used for comparison. Significance Statement Atmospheric conditions often indicate whether certain thunderstorms will produce tornadoes. However, sometimes multiple thunderstorms exist in a similar environment, and some produce tornadoes while others do not. Weather radar can identify signatures within thunderstorms that may give some indication of vertical motion, size sorting, and precipitation distributions. When multiple thunderstorms exist in a similar environment, there may be differences in these radar signatures that may indicate which thunderstorms are most likely to become tornadic. The key finding from this study is that pretornadic storms have larger radar-inferred updraft areas than neighboring nontornadic storms.