Oklahoma Thunderstorms on 29–30 April 1970. Part III: Tornado Characteristics Inferred from Damage Tracks

Abstract

Newspaper accounts and damage tracks surveyed by National Severe Storms Laboratory staff reveal characteristics of three tornadoes that struck the Oklahoma City area shortly after midnight on 30 April 1970. Few details emerge from surveying the first tornado (Storm F) except that its path crossed mostly open country and passed several kilometers northwest of Oklahoma City. Twin tornado cyclones (Mustang and Camelot), observed an hour later in Storm G, apparently produced multiple tornadoes that moved rapidly (80 m s−1) around the southern half of larger cyclonic circulations (hook echoes). Sporadic damage mostly at roof level suggests that the tornadoes often did not extend to the ground. Typically, debris was strewn in straight paths at an angle to the path of the tornado cyclone, suggesting tornado spin velocity less than speed of forward movement. Geometric relationship between a portion of one damage path and the path and forward speed of the tornado cyclone are the basis for estimating maximum winds at the ground to have been less than 160 m s−1. The nature of the structural damage suggests maximum winds were about 105 m s−1. It is concluded that the $6.3 million damage done by these storms was caused by relatively weak tornadoes (probably less than 25 m s−1 spin velocity) embedded within rapidly rotating tornado cyclones.