The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or 
Briefly, assuming that the Multivariate ENSO Index (MEI) has an average that will range between 0.00 and +1.25 (which is highly likely this coming winter), here are the average seasonal snowfall results for a number of past NAO-PNA combinations:
Code: Select all
NAO PNA Snowfall
- - 21.1"
- + 22.1"
+ - 15.3"
+ + 11.8"
Note:
- means that the PNA or NAO averages less than 0.0 for December-March; + means that the PNA or NAO averages above 0.0 for December-March.
In general, negative NAO situations tend to promote snowier winters for DCA (5 of 9 years with the MEI in the earlier-noted range saw 20" or more seasonal snowfall).
However, when the NAO and PNA have averaged negative while the PDO averaged +, DCA saw an average of 12.5" (1 of 2 seasons had 20" or more).
Conversely, positive NAO seasons have not been favorable for DCA (1 of 10 such seasons meeting the MEI parameter had 20" or more snowfall). However, the single season with more than 20" snowfall when the NAO was positive had a negative PNA and a positive PDO.
Finally, although the seasonal evolution has not reached the point where the NAO is ready to average negative and the PNA positive, there are hints in both the SSTAs and the global indices (I use global indices to help predict the NAO as the use of some of these indices appears to raise the overall correct sign to around 80%) that this season should see the PNA average > 0 and the NAO < 0. A lesser possibility is that the PNA and NAO both average < 0. I'll likely have a firmer idea on both these indices once the November global data is in.
All said, one should not yet write off DCA's prospects for snowfall. I do believe New England, especially Boston will see above to much above normal snowfall. But the proverbial window of opportunity has not yet slammed shut on DCA.
