Comparison of USA Tornado Days for Two Climatological Periods

This is a comparison of USA tornado days for two climatological periods suggesting a possible spatial shift in tornado alley. A tornado day is defined as a day with at least one tornado that has an intensity of (E)F1 or greater. The study encompasses a region of 20 states (AL, AR, GA, IA, IL, IN, KS, KY, LA, MI, MN, MO, MS, ND, NE, OH, OK, SD, TN, and WI). The analysis shows evidence of the traditional tornado alley shifting eastward into the Dixie states. The comparison is made by looking at two different time periods within the domain, where (1954-1983) is defined as the Cold Period I and (1984-2013) is defined as the Warm Period II. By counting the number of (E)F1-(E)F5 tornado days per state in each period, provided by NOAA's Storm Data archive, it is shown that the majority occurred in OK and KS during Period I but shifted east in Period II with the highest counts in LA and MS. The difference between the two periods supports the concept of an emerging new tornado alley that may be coincident with climate change.