Abstract Many tornadoes occur in rural forested regions of the world where traditional damage indicators are often unavailable to determine, or may underestimate, a tornado’s true intensity. Future versions of the EF scale are expected to include guidelines for treefall pattern matching to determine tornado intensity. This study explores the reliability and uncertainty of using tornado treefall patterns as a method for assessing the maximum 3-second gust speed and swirl ratio of tornadoes in forested regions. Through mathematical analysis, treefall patterns are determined to depend primarily on the ratio of the tornado’s radial, tangential and translational speeds, as well as the critical tree failure speed. Moreover, four typical types of tornado treefall patterns are differentiated based on vortex-tree failure locations relative to the tornado’s radius of maximum wind speed. As a result, when estimates for the critical tree failure and tornado translation speeds are known, treefall patterns can be consistently linked to an estimate of a tornado’s maximum wind speed and swirl ratio. The damage paths of four tornadoes, including the previously analyzed Alonsa, MB EF4 tornado, are analyzed using custom software implementing a Monte Carlo simulation for treefall pattern matching to estimate the maximum 3-second gust speed and swirl ratio, as well as the associated uncertainty. Of the three newly analyzed events, two are estimated to have higher EF Scale ratings than those suggested by the current Canadian EF-scale.
Butt et al. (Tue,) studied this question.