Winter Significant Tornado Variability in Relation to ENSO and the Gulf of Mexico

The vast majority of tornado related deaths are associated with those rated significant (EF2+). Despite low tornado frequency during the winter season (DJF; December, January, and February), tornadoes are rated significant most frequently in DJF, with tornado occurrence climatologically favoring the densely populated region of the southeastern United States. Previous research has shown that DJF tornado frequency is related to the El Niño-Southern Oscillation (ENSO). Such a relationship is physically reasonable; ENSO is the dominant mode of climate variability during DJF, generally reaching peak amplitude with decay following in spring.

The Oceanic Niño Index (ONI) has been frequently used to characterize ENSO, but the considerable internal variability of ENSO makes the use of a single index not sufficiently representative. Moreover, varying degrees of intensity in the oceanic component of ENSO can result in modulations to the canonical atmospheric counterpart, leading to downstream climate impacts across the contiguous United States that could influence significant tornado occurrence. Additionally, the state of the Gulf of Mexico (GoM) can result in modulations to tornado activity that can either enhance or detract the expected influence of ENSO. This presentation will explore the variability of DJF significant tornado frequency using GoM SSTAs and various ENSO intensities and indices, including: ONI, Niño 1+2, Niño 3, Niño 4, and Modoki indices. Atmospheric and SST characteristics of strong ENSO events featuring low significant tornado totals will be discussed, shedding light on the complex relationship between the climate system and DJF tornadic activity.