Differentiating Between Tornadic and Nontornadic Supercells Using Polarimetric Radar Signatures of Hydrometeor Size Sorting

Supercell storms are the most prolific producers of violent tornadoes, though only a fraction of supercells produce tornadoes. Past research into the differences between tornadic and nontornadic supercells have provided some insights but are of little utility to a real-time warning decision process. Operational weather radars provide consistent observations in real time, but conventional radar techniques have not been able to effectively distinguish between tornadic and nontornadic supercells. After the national radar network upgrade to polarimetric capabilities in 2013, a polarimetric signature frequently observed in supercells is the separation of low-level enhanced differential reflectivity Z(DR) and specific differential phase K-DP regions. We analyzed this signature in tornadic and nontornadic supercell cases and found that, although the separation distances are similar, the separation orientations are statistically significantly different. Tornadic supercells have orientations more orthogonal to storm motion and nontornadic supercells have more parallel orientations. Possible reasons for these differences are discussed. Plain Language Summary Supercell storms are responsible for a vast majority of violent tornadoes, but most supercells do not produce tornadoes at all. Finding differences between supercells that produce tornadoes and those that do not has been a goal of meteorologists for several decades and is important for issuing tornado warnings. Previous research has either used computer simulations or studied specific storms from specialized field campaigns. Neither of these are useful in a realistic tornado warning process. Weather radars provide constant monitoring of supercells, but techniques from the past few decades have been unsuccessful in finding differences between supercells that produce tornadoes and ones that do not. The national radar network was recently upgraded in 2013 and has provided new information. A new signature from the upgraded network is the separation of regions with large values of two different radar variables, which is analyzed in this study in a large number of tornadic and nontornadic supercells. We found that the separation distances are similar but the orientations are significantly different between tornadic and nontornadic supercells.