3B.3 A Two-Year Forecast for a 60–80% Chance of La Niña in 2017–18

Monday, 8 January 2018: 2:30 PM
616 AB (Hilton) (Austin, Texas)
Pedro DiNezio, Univ. of Texas, Austin, TX; and C. Deser, A. Karspeck, S. Yeager, Y. M. Okumura, G. Danabasoglu, N. Rosenbloom, J. Caron, and G. A. Meehl

Historical observations show that one in two La Niña events last for two consecutive years. Despite their outsized impacts on drought, these 2-year La Niña are not predicted on a routine basis. Here, we assess the predictability of 2-year La Niña using retrospective forecasts performed with a climate model that simulates realistic multi-year events, as well as with a statistical model based on observations. The skill of the retrospective forecasts allows us to make predictions for the upcoming 2017-2018 boreal winter starting from conditions in November 2015. These two-year forecasts indicate that the return of La Niña is more likely than not, with a 60% probability based on the climate model and an 80% probability based on the statistical model; the likelihood of El Niño is less than 8% in both cases. Retrospective verification of forecasts for historical 2-year events demonstrate the feasibility of long-range predictions of the duration of La Niña. These forecasts will be verified by the time of the conference.
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