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Influence of the El Niño/Southern Oscillation on tornado and hail frequency in the United States


The El Niño/Southern Oscillation (ENSO) is characterized by changes in sea surface temperature (SST) and atmospheric convection in the tropical Pacific, and modulates global weather and climate1,2,3,4. The phase of ENSO influences United States (US) temperature and precipitation and has long been hypothesized to influence severe thunderstorm occurrence over the US5,6,7,8,9,10,11. However, limitations12 of the severe thunderstorm observational record, combined with large year-to-year variability12,13, have made it difficult to demonstrate an ENSO influence during the peak spring season. Here we use environmental indices14,15,16 that are correlated with tornado and hail activity, and show that ENSO modulates tornado and hail occurrence during the winter and spring by altering the large-scale environment. We show that fewer tornadoes and hail events occur over the central US during El Niño and conversely more occur during La Niña conditions. Moreover, winter ENSO conditions often persist into early spring, and consequently the winter ENSO state can be used to predict changes in tornado and hail frequency during the following spring. Combined with our current ability to predict ENSO several months in advance17, our findings provide a basis for long-range seasonal prediction of severe thunderstorm activity.

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Figure 1: Composite mean anomalies of winter (December, January, February) hail and tornadoes conditioned on the winter ENSO state.
Figure 2: Composite mean anomalies of spring (March, April, May) hail and tornadoes conditioned on the spring ENSO state.
Figure 3: Mean spring environmental composite anomalies for upper level and surface winds, and for convective available potential energy by ENSO state.
Figure 4: Spring occurrence relative to climatology for the forecast box, and probability of climatological frequency by winter ENSO state.

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The authors are supported by grants from the National Oceanic and Atmospheric Administration (NA05OAR4311004 and NA14OAR4310185), the Office of Naval Research (N00014-12-1-0911) and a Columbia University Research Initiatives for Science and Engineering (RISE) award. The views expressed herein are those of the authors and do not necessarily reflect the views of NOAA or any of its sub-agencies.

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J.T.A. carried out production of all results and led writing of the paper and research design. M.K.T. contributed to the research design and assisted with statistical analysis. All authors participated in the interpretation of results and the writing and editing process.

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Correspondence to John T. Allen.

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The authors declare no competing financial interests.

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Allen, J., Tippett, M. & Sobel, A. Influence of the El Niño/Southern Oscillation on tornado and hail frequency in the United States. Nature Geosci 8, 278–283 (2015).

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