Scientists may have uncovered how sea-surface temperature patterns influence the number, strength and distributions of April tornado formation in the south-central region of the United States known as "Tornado Alley." Their results underscore how shifting climate patterns potentially affect tornado formation within seasons, which could help reduce fatalities and widespread property loss during peak tornado months - by facilitating improved predictions. In 2011, nearly 1,700 tornadoes were recorded in North America, resulting in more than 500 deaths and $10 billion in property and crop damage. The subsequent tornado season, in 2012, saw an estimated 900 tornadoes and 70 deaths. Seeking to better understand the potential causes underlying such year-to-year variations, J.-E. Chu et al. conducted a month-by-month analysis of tornado counts across North America spanning 1954 to 2016, with a focus on the springtime Tornado Alley twisters. The researchers found no significant connection between May tornado numbers and sea surface temperature patterns. This observation hints that tornadoes occurring in May are more strongly influenced by internal atmospheric processes. In contrast, they discovered that April tornado activity is strongly influenced by large-scale climate patterns. For example, the April tornados were more frequent when equatorial Pacific and eastern North Pacific waters were cooler and subtropical Pacific and western Atlantic waters were warmer. Based on these results, Chu and colleagues' findings suggest that shifting weather patterns within seasons--rather than seasonal averages alone--are important factors to consider in studies that measure the impact of climate change on tornado frequencies.
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