July 2016 SW Climate Outlook - La Niña Tracker

All oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) have returned to neutral conditions (Figs. 1-2). The development of a La Niña event in 2016 remains a distinct possibility, even while the timing and intensity remain relatively uncertain.

On July 14, the NOAA Climate Prediction Center (CPC) highlighted the persistent neutral conditions currently observed and identified some tension between statistical and dynamical models, the former predicting a later onset and weaker event than the latter. The CPC forecast took a middle ground between these models and forecast a 55–60 percent chance of a weak La Niña event starting sometime between August and October 2016. On July 19, the Australian Bureau of Meteorology maintained its La Niña watch but saw some recent declines in model projections that decreased the forecast probability to a 50 percent chance of a La Niña event developing. On July 21, the International Research Institute for Climate and Society (IRI) and CPC forecasts highlighted that while most of the oceanic and atmospheric conditions were indicative of a La Niña event forming, the trade winds had not yet shifted towards La Niña, and there was a lack of coupling between ocean and atmosphere that is crucial to the formation of a La Niña event. The IRI-CPC forecast still sees the formation of a La Niña event in 2016 as more likely than not, but with the timing delayed and the intensity of the event not likely to exceed weak status (Fig. 3). The North American multi-model ensemble characterizes the current model spread and highlights the variability looking forward to 2017, but the ensemble mean hovers close to weak La Niña status for fall and winter of the coming year (Fig. 4).

La Niña typically brings drier-than-average conditions to the Southwest, and it will be important to track both the timing and intensity of this event in relation to precipitation, temperature, snowpack, and water supply over the coming year. CLIMAS researchers are contributing to a La Niña information hub that will mirror the El Niño hub, with the goal of providing a curated set of news and forecast models regarding La Niña, as well as expert commentary and analysis on the possible impacts to the Southwest.

Visit climas.arizona.edu for more information.