Thursday, November 22, 2012

PDO Showing Signs of Transition

The Pacific Decadal Oscillation, or PDO, is showing signs of changing its phase as we move through the last month of fall.

The above image shows changes in sea surface temperatures (SST's) from September 2012 to October 2012. The blues signify a cooling temperature trend, while reds display warming of the waters. If we take a look at the north central Pacific in whole, we see a stark cooling trend coming around from east Asian waters to the waters south of the Aleutian Islands. Also, notice a slight warming trend focused in and to the north of the Aleutian Islands to the west coast of Canada, as far south as Baja California. This warming then moves west, forming a backwards 'C' around the cold pool.

PDO Phases
What we are seeing here is a vaguely textbook example of a positive PDO. In a positive PDO, a cold pool of water extends from East Asia and across much of the north Pacific. Warmer waters encompass this cold pool, as I described above as a backwards 'C'. In the negative PDO, the temperature anomalies change places, with cold waters forming a backwards 'C' around a warm pool.

Because the PDO is so complicated, I'll put the effects as simple as possible. A positive PDO tends to bring cooler than normal temperatures to much of the nation, while a negative PDO brings warmer than normal temperatures to the Lower 48. So, if we do have this PDO switch from its current negative phase to a positive phase, we could see a cooler winter than I had accounted for.

Exciting times ahead!


1 comment:

Eric said...

This is great news, because warm AMO, cold PDO (briefly flipping to positive), plus a favorable QBO and AO/NAO, and the US could really be in for it this winter. If we do indeed see a flip to a warm PDO would be comparable to the cold winters of late 1970s.