Adjusted Tornado Probabilities

Abstract

Tornado occurrence rates computed from the available reports are biased low relative to the unknown true rates. To correct for this low bias, the authors demonstrate a method to estimate the annual probability of being struck by a tornado that uses the average report density estimated as a function of distance from nearest city/town center. The method is demonstrated on Kansas and then applied to 15 other tornado-prone states from Nebraska to Tennessee. States are ranked according to their adjusted tornado rate and comparisons are made with raw rates published elsewhere. The adjusted rates, expressed as return periods, are <1250 y for four states, including Alabama, Mississippi, Arkansas, and Oklahoma. The expected annual number of people exposed to tornadoes is highest for Illinois followed by Alabama and Indiana. For the four states with the highest tornado rates, exposure increases since 1980 are largest for Oklahoma (24%) and Alabama (23%).

The Characteristics of United States Hail Reports: 1955-2014

“…Several studies have proposed that population can be used to adjust tornado report frequency (Elsner et al 2013;Widen et al 2013). However we illustrate here using a case study of the Texas panhandle that considering this factor alone may not be an effective approach to remove inhomogeneities in the reported hail data.…”

“…We do not claim to provide a comprehensive description of all nonmeteorological characteristics the hail dataset. We also do not intend to question the reports or source of any one CWA over any other, but only to illustrate that the challenges of the hail report data extend beyond population or easily modeled corrections that may be possible for tornadoes (Widen et al 2013;Elsner et al 2013). Characteristics on a local or county scale resulting from local office policy, observation sources and individual forecasters likely exist beyond what is detailed here, and these nuances may only be in the knowledge of local forecast offices or individuals.…”

Tornado Damage Ratings Estimated with Cumulative Logistic Regression

“…For each tornado, we compute the distance between the genesis location and the nearest city/town (Elsner et al 2013;Widen et al 2013) are based on the 2010 U.S. Census data [obtained from Steiner (2019) and accessed through the ''USAboundaries'' package (Mullen and Bratt 2018) in the R software package] and range from a few hundred people to more the eight million people. The distance between a tornado and the nearest city/town serves as a proxy for the potential number of damage targets.…”