A Spatiotemporal Perspective on the 31 May 2013 Tornado Evacuation in the Oklahoma City Metropolitan Area

On 31 May 2013, an extremely large and violent tornado hit near the town of El Reno, Oklahoma, a small town in the Oklahoma City metropolitan area. The size and intensity of this tornado, coupled with the fact that it was heading toward Oklahoma City, prompted local broadcasters to warn residents to evacuate their homes and head south if they could not shelter belowground. This warning led to a large-scale evacuation of the metropolitan area and massive traffic jams on the interstates and major highways that could have caused casualties in the hundreds if the tornado had not dissipated before reaching Oklahoma City. The focus of this study was to understand the magnitude of the 31 May 2013 evacuation through the evaluation of traffic volume data and to determine how frequently such evacuations occur in Oklahoma City and other metropolitan areas. We found that of the six metropolitan areas tested, only Oklahoma City had mass anomalous traffic reversal (ATR) days (days with a mass evacuation signal) with 31 May 2013 having the largest mass ATR day by far. Despite the rarity of mass ATR days, the potential consequences of a large, violent tornado hitting gridlocked traffic is significant, and we recommend that communicators encourage more local sheltering options.