2015––2016 El Niño Tracker
El Niño conditions continued their active decline (Figs. 1-2), and consensus is that they have reached ENSO-neutral status at the time of this writing. Forecast discussions focused on the decline of atmospheric and oceanic anomalies that characterize an El Niño event—convective activity, equatorial sea surface temperatures, and trade winds—and forecasters saw consistent evidence of a return to ENSO-neutral status across these indicators. Seasonal ENSO outlooks coalesced around La Niña conditions emerging by summer or fall 2016, with relatively high certainty that La Niña conditions would be in place sometime by mid-to-late 2016.
On June 7, the Australian Bureau of Meteorology maintained its outlook at La Niña Watch status, noting that the tropical Pacific Ocean was in an ENSO-neutral state, with a 50 percent probability of a La Niña event developing in 2016. On June 9, the NOAA-Climate Prediction Center (CPC) issued a final El Niño Advisory, while maintaining a La Niña Watch. The CPC identified atmospheric and oceanic anomalies as reflecting ENSO-neutral conditions and forecast La Niña conditions would develop over the summer, with a 75 percent probability of a La Niña during fall and winter 2016-2017. On June 10, the Japan Meteorological Agency identified that El Niño conditions ended in late spring 2016, with an increasing likelihood of La Niña developing over summer and into fall. On June 16, the International Research Institute for Climate and Society (IRI) and CPC forecasts identified ENSO-neutral conditions in oceanic and atmospheric indicators, with La Niña emerging by late July or August and lasting through fall and winter (Fig. 3). The North American multi-model ensemble currently shows the decline from strong El Niño status to neutral conditions, as well as a relatively rapid swing to La Niña conditions by summer (Fig. 4).
As very clearly experienced during the El Niño event of 2015–2016, there is no guarantee that a given event will meet expectations (see El Niño tracker in the May 2016 Southwest Climate Outlook for more details). That said, it is important to note that La Niña events are associated with decreased cool-season precipitation in the Southwest. This is a more reliable pattern in terms of forecasts and predictions, with La Niña events being more reliably dry than El Niño events are reliably wet, and considerable variability between wet and dry in ENSO-neutral years. With a La Niña forecast on the horizon for winter 2016–2017, drier-than-average cool-season precipitation totals are a likely outcome, with implications for long-term drought and water storage concerns in the Southwest.