BlogThe Pacific Decadal Oscillation is the Coldest Since 1955

June 20, 2022

With a positive PDO, sea surface temperatures (SSTs) are typically warmer than normal near the west coast of North America with cooler than normal SSTs present in the central North Pacific Ocean. In a negative PDO, this setup is opposite, with cooler than normal SSTs near North America’s west coast and warmer than normal SSTs in the central North Pacific Ocean. As its name suggests, the PDO tends to remain in one of these two phases for as long as 20-30 years before switching to the other phase or occasionally near neutral for a relatively brief time.

A positive PDO typically means temperatures (mostly in winter) are warmer than normal in the Pacific Northwest, northern Rockies, Northern Plains, Upper Midwest, and California, and cooler than normal in the Southern Plains, Southeast, southern Midwest, mid-Atlantic and Northeast.  . A negative PDO usually means the opposite, with slower periods of global warming associated with increased upwelling in ocean waters. This can have impact on long-range forecasts. The PDO remained generally in the positive phase from the late 1970s through the late 1990s, a negative phase generally from the late 1990s to around 2014,

In 2021, the PDO moved further into the negative (colder) phase. The year as a whole had the lowest (coldest) PDO value since 1955 and the fifth coldest calendar-year average PDO in 168 years of records. October 2021 saw the coldest PDO value since October 1955 and the 11th coldest month PDO value on record since 1854. Combined with cold PDO values in November and December, the October-December 2021 period had the 6th lowest three-month period on record (eliminating overlapping periods). It’s also the coldest fall or winter PDO on record. The late 1940s to mid-1950s had some of the coldest PDO values and some of the coldest winters and largest snowfalls on record in the Pacific Northwest.

Thus, there is the potential for this cold PDO to continue for at least another few years or longer, leading to cooler than normal winter temperatures in the Pacific Northwest and warmer than normal winters in much of the Eastern U.S. If it lasts for some time and/or near its recent magnitude, there’s the possibility of more difficult forecasts particularly for the West Coast with increased rain or snow potential in such a pattern, and possibly increased rain or winter severe weather events in the Southeast.

For the most updated PDO index data, visit the National Centers for Environmental Information at https://www.ncdc.noaa.gov/teleconnections/pdo/.


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