Modulation of Annual Cycle of Tornadoes by El Niño–Southern Oscillation

Abstract

Long-term trends suggest shifts toward earlier tornado season peaks, and yet fail to examine the role of year-to-year climate variability. Here, El Niño–Southern Oscillation phase is demonstrated to influence annual cycle characteristics of United States tornadoes. Observations and favorable environments show substantial modification of the peak spatial distribution and the temporal onset of tornado occurrence. La Niña produces an earlier annual peak probability by 1.5–2 weeks, with a higher overall fraction of events in March and April. In contrast, El Niño leads to a week delay in the maximum probability and enhances a second peak in the fall months. Consequently, this suggests that climate change is not the sole driver of changes to seasonal onset and peak, and climate variability plays an important role in modulating the annual cycle.