Pacific Decadal Oscillation – Say What?

What is the Pacific Decadal Oscillation?

Dedicated skiers around North America have come to anticipate the news from climate researchers regarding ENSO (La Nina/El Nino) each season. Essentially a shift in sea surface temperatures in the Pacific – La Nina bringing cooler waters to the Pacific shores and El Nino bringing warmer waters – ENSO has proven to have a direct impact on snowpacks around the west (read a past Off-Piste Magazine article about ENSO) . Well, it turns out there’s a longer term sea surface temperature trend that impacts our winter weather, especially that of the Pacific Northwest including Alaska and British Columbia. It’s called the Pacifc Decadal Oscillation or PDO.

Broadly speaking, PDO can be viewed as similar to ENSO in that it represents a trend in sea surface temperatures in the Pacific – either warmer or cooler, but the PDO reflects these trends in decades not annual changes. But unlike ENSO, PDO has the most impact on the weather of northwestern North America, versus that of equatorial regions.

Pacific Decadal Oscillation Values

Currently, the PDO appears to be headed into a cool phase (see graphic above). What does this mean for Northwest skiers? In general, it means cooler and wetter, statistically speaking. The cool phase PDO brings cooler water along the pacific shore and favorably impacts storm tracks from the Pacific for a greater chance of precipitation here in the Northwest.

Sounds great to me, but of course it’s not that simple. Climate scientists also believe  there’s evidence that ENSO is currently moving toward El Nino for the winter, its warm phase, which has the opposite effect on the Northwest climate. According to Nathan Mantua, Ph. D. at University of Washington in Seattle (read regional PDO guru), when the PDO and ENSO are in sync – both in a cool or warm phase – the ENSO influence tends to be amplified. When the two cycles are out of phase, like the current models suggest, the PDO will reduce the impact of ENSO.