A cold and stormy November possible

Taking a look at the September 500mb height anomalies, three distinct regions are evident.


I created a time series for the three areas, and sorted the years to find a best match for each one. Using the each time series, I also made a custom series (Area B + Area C - Area A). I took the top 20 (minus 2008 which was first as to be expected) for possible analogs and sorted through them, eliminating El Nino and +AAM years as well as years where the custom data was skewed due to a strong anomaly in only one of the areas but not the rest. The resulting years (in chronological order) were 1949, 1956, 1960, 1961, 1963, 1967, 1972, 1974, 1989, 1995, 1999, 2007.


As you can see, the average of the list of analogs returns a fairly close match to the September 2008 pattern.

Because features in the atmosphere are interconnected to some degree, using the analogs presented, we can get a general idea for the future. Roll forward analogs generally work best in the 25+ day range. This is because before then there is a transitional period during which the signals from each analog are widely spread and average to a weak, blurry signal.


In this case, the October analog average does not have high magnitude anomalies, however November features an node in the analogs. There is a strong signal at this time for +PNA ridging with a trough over the eastern US. In fact 11 of the 12 analogs show below normal heights in the east with the only exception being 1999 during which the mean ridge axis was further east.





The MJO should be into octant 5 of phase space by November 15 to 18, during which time a negative NAO develops. At this point in time, the possibility of a measurable snowfall between the 18th and the 25th is looking good.