Quantifying the separation of enhanced Z_DR and K_DP regions in nonsupercell tornadic storms

Tornadoes associated with nonsupercell storms present unique challenges for forecasters. These tornadic storms, although often not as violent or deadly as supercells, occur disproportionately during the overnight hours and the cool season-times when the public is more vulnerable. Additionally, there is significantly lower warning skill for these nonsupercell tornadoes compared to supercell tornadoes. This study utilizes dualpolarization Weather Surveillance Radar-1988 Doppler (WSR-88D) data to analyze nonsupercell tornadic storms over a three-and-a-half-year period focused on the mid-Atlantic and southeastern United States. A signature found in a large number of cases is the separation of low-level specific differential phase K_DP and differential reflectivity Z_DR enhancement regions, thought to arise owing to size sorting. This study employs a new method to define the ''separation vector,'' which comprises the distance separating the enhancement regions and the direction from the K_DP enhancement region to the Z_DR enhancement region, measured relative to storm motion. While there is some variation between cases, preliminary results show that the distribution of separation distance between the enhancement regions is centered around 3-4 km and tends to maximize around the time of tornadogenesis. Apreferred quadrant for separation direction is found between parallel and 908 to the right of storm motion and is most orthogonal near the time of tornadogenesis. Further, it is shown that, for a given separation distance, separation direction increasing from 08 toward 908 is associated with increased storm-relative helicity.