2015 El Niño Tracker
El Niño conditions continued for an 11th straight month, putting us squarely in the middle of a strong El Niño event that will be among one of the strongest events on record. Forecasts focused on the persistence of sea surface temperature (SST) anomalies (Figs. 1–2) and weakened trade winds, enhanced convective activity in the central and eastern Pacific, and El Niño-related ocean-atmosphere coupling. Models continue to forecast a strong El Niño event that will last through spring 2016, but we are starting to see signs of decline in the overall strength of the event.
On Jan. 12, the Japan Meteorological Agency identified ongoing El Niño conditions as having reached their “mature stage” in the equatorial Pacific in November–December 2015, with likely gradual weakening during the months ahead. On Jan. 14, the NOAA-Climate Prediction Center (CPC) extended its El Niño advisory and said the current atmospheric and oceanic anomalies reflect a strong El Niño that will persist through most of the spring, transitioning to ENSO-neutral by late spring or early summer. The CPC noted, however, that the “exact timing of the transition is difficult to predict.” On Jan. 19, the Australian Bureau of Meteorology maintained its tracker at official El Niño status, with the event likely having peaked and ocean temperatures showing signs of gradual cooling. On Jan. 21, the International Research Institute for Climate and Society (IRI) and CPC forecasts indicated that all oceanic and atmospheric variables were indicative of a strong El Niño event, with consensus centering on strong El Niño conditions that will persist through spring 2016 (Fig. 3). The IRI/CPC briefing also indicated El Niño strength peaked in November–December, but that this was a “broad peak” with a gradual decline and the El Niño event would remain strong through late spring 2016. The North American multi-model ensemble currently shows a strong event extending into 2016 with gradual weakening heading into spring and summer (Fig. 4).
So what does this mean for the region? Even though forecasts are looking at the eventual decline of the El Niño signals, we are in the middle of a strong El Niño event. For the Southwest, the current seasonal forecasts and past events suggest we should see well above-average cumulative precipitation totals throughout our cool season (October–March), but we should also expect periods of inactivity between storms. Even though the 2015–2016 El Niño event “peaked” in November-December, we see impacts in the Southwest as they lag behind this spike in intensity, which means that we look to late winter and early spring as the most likely times to see increased storm activity associated with the El Niño signal. This doesn’t mean we can’t or won’t see increased activity outside of this window, but the default state for the desert Southwest is dry; even a strong El Niño event can only alter that system so much. We won’t be able to fully dissect and judge the 2015–2016 El Niño event until we see just how much rain and snow fell over the entire cool season. Given what we know about past events, our best bets for receiving above-average precipitation will be in February and March, or even April.
Looking at the 1997–1998 event—the strongest El Niño event on record—most of Arizona and New Mexico received below-average rain and snowfall for all of January before returning to normal or above-normal precipitation in February and March (Figs. 5–8).