Pattern Change En Route?

For the past few weeks or so long-range computer forecast models had hinted that we would see a major pattern change as early as Thanksgiving and we would see much colder weather work into the Northeastern United States.  This, however, has been pushed off but there are some really strong signals that perhaps around the 8th of December this pattern change occurs but the question is for how long?

The latest 8-10 day 500mb height anomaly forecast from the European model and GFS model continue to suggest that we will see strong ridging develop across northern Canada and Arctic region.  While these models have been showing this in the 8-10 day mean for quite some time the "8-10" day never seems to arrive.  However, there is growing consensus that this will indeed occur and perhaps around December 8th.  Ridging in this area would do one of a few things; it would work to further weaken the polar vortex and also allow to to become displaced further to the south which would enhance the likelihood for much colder Arctic air to sink southward into the United States:

 
The support lies within the forecasts for some of the major global teleconnection indices such as the Eastern Pacific Oscillation (EPO), Arctic Oscillation (AO), and North Atlantic Oscillation (NAO).  One of the major teleconnection patterns, the Pacific-North american (PNA) is not very supportive, however, and with this I do think that the pattern change could be rather brief.  Looking into the major global indices, long-range forecasts suggest that the EPO and NAO will really become negative around December 8th.  When the NAO and EPO are negative this enhances the likelihood for really cold Arctic air to work southward into the United States.  The forecasts for the AO though are much more uncertain (as we will see below).  Given the projected 500mb height pattern featured above the more likely scenario will be for the AO to tank negative as well.  The forecast for the PNA is to also become negative and that actually would enhance potential for a trough out in the western United States which can support ridging here in the east.  If, however, the EPO/NAO are quite negative this would suppress ridging:

So what can we expect?  I think there are some strong signals for at least a brief pattern change around the 8th of December and we will have a period of very cold weather.  The big question is does that mean we will get snow?  That is not so easy to answer, however, if the pattern remains as active as it has been this past week there is a good bet we could have our first big snow threat of the season right around this time.  Hopefully (for snow lovers) we can cash in because this pattern change may be brief and we could return to more a more temperate regime.