Adjusted Tornado Probabilities

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 getting hit by a tornado that uses the average report density estimated at city centers. 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 less than 1,000 years for four states, including Oklahoma, Arkansas, Mississippi and Alabama. The expected annual number of people exposed to tornadoes is highest for Illinois followed by Alabama, Indiana, and Oklahoma. For the four states with the highest tornado rates, exposure increases since 1980 are largest for Oklahoma and Alabama.