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EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION
CLIMATE PREDICTION CENTER/NCEP/NWS
and the International Research Institute for Climate and Society 10 December 2020
ENSO Alert System Status: La Niña Advisory
Synopsis: La Niña is likely to continue through the Northern Hemisphere winter 2020-21 (~95% chance during January-March), with a potential transition during the spring 2021 (~50% chance of Neutral during April-June).
La Niña persisted during November, as indicated by well below-average sea surface temperatures (SSTs) extending from the Date Line to the eastern Pacific Ocean. Most of the weekly indices fluctuated through the month, with the westernmost Niño regions Niño-4 and Niño-3.4 ending up around -1.0oC. The negative equatorial subsurface temperature anomalies (averaged from 180°-100°W) weakened slightly last month, but continued to reflect below-average temperatures from the surface to 200m depth in the eastern Pacific Ocean. The atmospheric circulation over the tropical Pacific Ocean remained consistent with La Niña. Over the western and central tropical Pacific Ocean, low-level wind anomalies were easterly and upper-level wind anomalies were westerly. Tropical convection continued to be suppressed from the western Pacific to the Date Line. Also,both the Southern Oscillation and Equatorial Southern Oscillation indices were positive. Overall, the coupled ocean-atmosphere system indicates the continuation of La Niña.
A majority of the models in the IRI/CPC plume predict La Niña (Niño-3.4 index less than -0.5°C) to persist through the Northern Hemisphere winter 2020-21 and to weaken through the spring. Supported by the latest forecasts from several models, the forecaster consensus is for a moderate strength La Niña (Niño-3.4 index values between -1.0oC and -1.5oC) during the peak November-January season. In summary, La Niña is likely to continue through the Northern Hemisphere winter 2020-21 (~95% chance for January-March), with a potential transition during the spring 2021 (~50% chance of Neutral during Apr-Jun; click CPC/IRI consensus forecast for the chances in each 3-month period).
La Niña is anticipated to affect climate across the United States during the upcoming months. The 3-month seasonal temperature and precipitation outlooks will be updated on Thursday December 17th.