The Role of Multiple-Vortex Tornado Structure in Causing Storm Researcher Fatalities

Abstract

nd violent tornado/multiple-vortex mesocyclone (MVMC) tracked east and northeastward near El Reno, Oklahoma, on 31 May 2013, causing eight fatalities, including storm chasers/researchers attempting to deploy in situ instrumentation. Subvortices moved within and near the MVMC, some in trochoidal-like patterns, with ground-relative translational velocities ranging from 0 to 79 m s?1, the fastest ever documented. Doppler on Wheels (DOW) measurements in one of these subvortices exceeded 115 m s?1 at 114 m AGL. With assumptions concerning radar-unobserved components of the velocity, peak wind speeds of 130?150 m s?1 are implied, comparable to the strongest ever measured. Only enhanced Fujita scale 3 (EF-3) damage was documented, likely because of a paucity of well-built structures and the most intense winds being confined to small, rapidly moving subvortices, resulting in only subsecond gusts. The region enclosing the maximum winds of the tornado/MVMC extended ~2 km. DOW-measured winds > 50 m s?1 (> 30 m s?1) extended far beyond the radius of maximum winds (RMW) extending >5 km (7 km), comparable to the widest ever documented. A strong multiple-vortex anticyclonic tornado with dual-polarization debris signatures is documented. A subvortex tracking eastward within the larger tornado/MVMC intensified, moved north, and then moved northwestward, becoming briefly nearly stationary near/over a research team's vehicle, transporting it ~600 m generally eastward, killing the team. An experienced media team's vehicle was destroyed inside the tornado/MVMC, resulting in injuries. The circumstances leading to these incidents are analyzed using DOW data. The anomalous?and likely unpredictable in real time?path of the interior subvortex likely contributed to these deaths and injuries. The risks associated with chasing and scientific missions near and particularly inside large and complex MVMC/tornado vortices are discussed.