Ground-based Damage Survey and Radar Analysis of the El Reno, Oklahoma Tornado

On 31 May 2013, an intense, multiple-vortex tornado meandered through sparsely populated areas south of El Reno, Oklahoma. This exceptionally wide tornado (4.2 km) took a complex path, rapidly changing in both speed and direction. Eight people were killed in the tornado, all in vehicles, including three severe storm researchers. Storm survey teams were dispatched to the area the following day and rated various damage indicators (DIs). The maximum damage rating was determined to be EF-3. In addition, the tornado was well sampled by the University of Oklahoma RaXPol radar at close range. The radar obtained high temporal and spatial resolution velocity data indicating instantaneous winds of at least 135 m/s very close to the ground. The intense winds were present in very small sub-vortices within the larger tornado circulation. Analysis of the high resolution radar data combined with the results of the ground damage survey indicated that none of these intense sub-vortices impacted any structures. So despite the measured wind speeds, surveyors could not find any damage that would support a rating higher than EF3 based solely on the damage indicators used with the EF scale. In this paper, we will discuss some of the pros and cons in using radar data to augment EF-scale ratings and present the results of our ground-based damage survey.