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CLIMAS SW Climate Outlook - ENSO Tracker June 2017 | CLIMAS


CLIMAS SW Climate Outlook - ENSO Tracker June 2017

Friday, June 16, 2017

Oceanic and atmospheric indicators of the El Niño-Southern Oscillation (ENSO) are still within the range of neutral (Figs. 1-2), although sea-surface temperatures more consistently hint at borderline El Niño conditions compared to atmospheric indicators. Outlooks and forecasts generally agree that ENSO-neutral conditions will persist through the summer and is the most likely scenario for the rest of 2017. A lingering possibility remains of an El Nino event developing later this fall, but forecasts since last month have shifted further from that likelihood.

On June 6, the Australian Bureau of Meteorology maintained its El Niño Watch with a 50-percent chance of an El Niño event in 2017, but noted indicators have remained mostly unchanged for multiple weeks, “suggesting El Niño development has stalled for now.” On June 8, the NOAA Climate Prediction Center (CPC) observed that oceanic and atmospheric conditions were consistent with ENSO-neutral conditions, but recent model runs led CPC forecasters to shift to a 50-55-percent chance of ENSO-neutral conditions in 2017 and a 35-50 percent chance of El Niño. On June 9, the Japanese Meteorological Agency (JMA) identified a continuation of ENSO-neutral conditions with a 70-percent chance of El Niño conditions until fall 2017, noting that oceanic and atmospheric conditions “indicate no clear signs of El Niño development.” On June 15, the International Research Institute for Climate and Society (IRI) and CPC identified ENSO-neutral as the most likely outcome in 2017, with a 40-to-45-percent chance of an El Niño in 2017 (Fig. 3). The North American Multi-Model Ensemble (NMME) is borderline weak El Niño as of June 2017, and while the model spread indicates a wide range of possible outcomes for the rest of 2017 (Fig. 4), the ensemble mean indicates ENSO-neutral as the most likely outcome (but with a weak El Niño event still within the range of plausibility), which is reflected in the uncertainty in the CPC and IRI/CPC outlooks.

Summary: The lack of atmospheric indicators of El Niño and the borderline status of sea-surface temperature anomalies have strengthened the forecaster consensus that ENSO-neutral is the most likely scenario for the remainder of 2017. It is too early to entirely rule out an El Niño event later this year, but the timing and intensity of this plausible but increasingly unlikely El Niño event is still relatively uncertain. There are two key takeaways from the current outlooks and forecasts. One, there is a near-zero probability of a La Niña event in 2017. Given that the Southwest shifts toward warmer and drier winter conditions in La Niña years, this is a welcome alternative. Two, given the relatively weak correlation between cool-season precipitation and weak El Niño events, whether ENSO-neutral or weak El Niño conditions ultimately prevail, the overall seasonal outlook for the Southwest would look relatively similar.

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