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SW Climate Outlook - ENSO Tracker - July 2017 | CLIMAS


SW Climate Outlook - ENSO Tracker - July 2017

Friday, July 21, 2017

Oceanic and atmospheric indicators are still within the range of neutral (Figs. 1-2), although sea-surface temperatures have hinted at borderline El Niño conditions. Seasonal outlooks and forecasts generally agree that ENSO-neutral conditions are the most likely outcome for the remainder of 2017, albeit with a lingering possibility of an El Niño event by winter 2017-2018.

On July 10, the Japanese Meteorological Agency (JMA) identified a continuation of ENSO-neutral conditions with an 80-percent chance of them extending through fall 2017. On July 13, the NOAA Climate Prediction Center (CPC) observed that oceanic and atmospheric conditions were consistent with ENSO-neutral conditions, maintaining a 50-55-percent chance of ENSO-neutral conditions in 2017 and a 35-45-percent chance of an El Niño. On July 18, the Australian Bureau of Meteorology effectively ended their El Niño watch, citing little evidence for anything other than neutral conditions at this point. On July 20, the International Research Institute for Climate and Society (IRI) and CPC identified a 35-40-percent chance of an El Niño in 2017 (Fig. 3) with “ENSO-neutral as the most likely condition during 2017.” The North American Multi-Model Ensemble (NMME) is ENSO-neutral as of July 2017. The model spread indicates a range of outcomes for the rest of 2017 (Fig. 4), but the ensemble mean indicates ENSO-neutral as the most likely outcome, yet allowing that a weak El Niño event is plausible.

Summary: The lack of atmospheric indicators of El Niño and the borderline status of sea-surface temperature anomalies have further contributed to forecaster consensus that ENSO-neutral conditions are the most likely outcome for 2017. An El Niño event remains possible but looks increasingly unlikely. As with last month, two key conclusions can be drawn from the current outlooks and forecasts. One, the probability of a La Niña event in 2017 is near zero, which is good news considering La Niña winters are often warmer and drier than normal in the Southwest. Two, given the relatively weak correlation between cool-season precipitation and weak El Niño events, it doesn’t really matter whether this winter ultimately turns out as ENSO-neutral or weak El Niño, as the winter seasonal precipitation outlook for the Southwest will encompass a wide range of possible outcomes, including both wetter and drier than normal conditions.