Substantial Pattern Change Expected as We Move into December

For those who love cold and the potential for lots of snow some good news exists as we move into and through the first week of December. For a while now, long-range teleconnection patterns have all indicated a major shift within the northern hemispheric pattern would occur which would favor major cold into the eastern United States as well as the possibility for increased storm chances.

Last night's 8-10 day mean 500mb height anomalies from the Euro (image on the left) and GFS (on the right) both indicate an extremely favorable pattern for some significant cold to pour into the eastern United States.  Both models indicate extreme blocking developing across the north-central Atlantic extending into Greenland (indicating a rather robust negative phase of the North Atlantic Oscillation (NAO) along with substantial ridging developing across the far western United States, extending northward into far western Canada and into Alaska (indicating a positive phase of the Pacific North-American teleconnection pattern (PNA) and negative phase of the Eastern Pacific Oscillation (EPO):

The configuration of the northern hemispheric pattern above is extremely favorable for very cold air to pour right into the eastern half of the United States.  There is a great deal of model support as well, especially within the GFS ensembles (unfortunately I don't have permission to post Euro ensemble data) for the AO, NAO, and EPO to tank and for the PNA to sharply rise:

While we recently are in a rather low state of angular atmospheric momentum (AAM) the forecasts are for the low state to relax with AAM hedging more towards the "circle of death".  Typically, when the atmosphere is in a really low AAM state, especially when La Nina forcing is present, this will favor troughs to dig into the western United States with ridging developing and strengthening across the southeastern United States. The extreme high latitude blocking, however, would work to suppress any ridge development across the southeastern United States:

There is also stratospheric support for blocking to develop as computer forecast models all indicate the likelihood for warming to occur within the stratosphere above the far north latitudes which will work to weaken the polar vortex and favor southward displacement. 

All in all the signals have been in place for quite some time on the potential for a rather significant pattern change to occur and one that will favor some major cold to spill into the eastern United States.  At the same time, this projected pattern will also become quite active.  With plenty of cold air available we'll have to certainly watch for snow events! One thing to also keep in mind is, if the blocking becomes as extreme or perhaps even more extreme than modeled, this could lead to a suppressed storm pattern meaning the storm track is well south of New England or well off the coast.  Regardless, for those who like interesting winter and root for snow and cold you may be in luck!