Cool Phase of the Pacific Decadal Oscillation Strengthens

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PDO discussion: Dr. Nate Mantua, PDO Expert at the NOAA/NMFS Southwest Fisheries Science Center reports that the March 2021 Pacific decadal oscillation index was -1.17 which represents moderate-to-strong cool phase. During March the -PDO regime present since early last year intensified to the strongest level during this 14-15 month-long cool regime. The last time a monthly -PDO index of this intensity was observed was last November and prior to that time summer of 2013 and 2012. The Climate Impact Company PDO analog forecast suggests the PDO has entered a possible multi-year cool regime last observed in 2010-12, 2007-09 and with the strong La Nina of 1998-00. There is a tendency for -PDO regimes to run parallel with La Nina. In each of the previous multi-year -PDO regimes of the past 25 years La Nina was present at varying intensity. Current ENSO forecasts project neutral ENSO into mid-year but La Nina may return later in 2021 and possibly faster if the -PDO pattern continues especially at the current intensity. During -PDO regimes there is a tendency for northern U.S. wet climate and southern U.S. (including California) dry-to-drought climate. There is dependency on the North Atlantic SSTA regime on these historical precipitation relationships.