Dissipation Characteristics of Long-Duration Tornadoes

WSR-88D radar data from a large sample of 2012-15 supercell cases are investigated to identify common tornado signature (TS) and tornadic vortex signature (TVS) behaviors prior to tornado dissipation. Based on the results of past case studies, four characteristics of TS/TVSs associated with tornado dissipation are identified: decrease in the value of TS/TVS ΔV, change in the storm-relative motion of the TS/TVS, increase in TS/TVS inclination angle, and increase in TS/TVS horizontal displacement from the main storm updraft. Polarimetric data are used to identify the approximate location and motion of storm updrafts. Since all four behaviors rely on changes to signature characteristics in time, only cases in which the reported tornado had at least 20 min of continuous data at the end of its life cycle within 60 km of a WSR-88D system are examined. These two conditions ensure that the aforementioned quantities can be determined within ~500 m of the surface at several times despite the relatively coarse spatial and temporal resolution of WSR-88D systems. Relevant results will be presented and discussed with a focus on characteristics that show promise as future tornado nowcasting aids.