A 2 year forecast for a 60-80% chance of La Niña in 2017-2018

Historical observations show that one in two La Nina events last for two consecutive years. Despite their outsized impacts on drought, these 2 year La Nina are not predicted on a routine basis. Here we assess their predictability using retrospective forecasts performed with a climate model that simulates realistic multiyear events, as well as with an empirical model based on observed predictors. 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 2 year forecasts indicate that the return of La Nina is more likely than not, with a 60% probability based on the climate model and an 80% probability based on the empirical model; the likelihood of El Nino is less than 8% in both cases. These results demonstrate the feasibility of predictions of the duration of La Nina.