History Says Arctic Blasts in January Follows Mundane December
PDO Record vs. Portland Temp Record?
The November PDO (Pacific Decadal Oscillation) reading was released today. November's reading of -2.33 was the third lowest November reading in history for that particular month. November 2011 only lags November 1955 at -3.08 and November 1950 at -2.46. It is also the 14th lowest month of the nearly 1,345 months on record (1900-2011). More than 99.2% of months on record were higher than this November. Nate Mantua and I both agree that it is also interesting to note that Portland will likely set a new all-time record for least number of 60 degree days in a calendar year at the airport (1940-2011) at the end of this month. Can you guess what years are in the #2 and #3 position for least number of 60 degree days at the airport? Yep, 1950 and 1955! The graph sent out last week listing the fewest 60 degree days in Portland history seems to correlate well with the graph of historically low PDO readings. Taking it one step further, Portland experienced both arctic air and snow in the January to March time frames of those winters (1951 and 1956) after relatively mundane Decembers. Is this month's stagnant ridge over the west coast and strongly negative PDO just "the calm before the storm?"
President, Oregon Chapter of the American Meteorological Society