Overall, I remain very optimistic about the end of this month, even if the next week or so will be an unabated blowtorch.
There are a couple of pattern drivers that lead me to believe that a pattern change is on the way, both of which have been discussed in this thread already!
1) The tropical forcing. We are currently in phase 6, and there is considerable agreement that we will enter phase 7 (and perhaps 8!) at high amplitude. This is shown by the RMM plots as well as standard OLR anomalies:
Phase 7 in December and January in -ENSO are correlated with very cold patterns for the E US as a whole:
Therefore, I do believe that the MJO will have a positive effect on the pattern. There is a chance that the La Nina could destructively interfere with the propagation of the MJO, but the overall weak status of the ENSO state as well as the very high confidence of propagation overall lead me to believe that this is unlikely.
2) The Scandinavian ridging that is going to develop in the medium range with very high confidence. Both major ensembles are in great agreement that a highly anomalous Scandinavian ridge is going to form. A 2 sigma ridge will certainly have an impact on our pattern. These cutoff ridges are known to retrograde towards the NAO domain and provide intense blocking (March 2018) as well as provide heat fluxes to disrupt the SPV, which is also being shown on modeling as well. This is also coupled with a strong MJO pulse into 6/7, which has been known to help disrupt the SPV as well. Both of these may work in tandem to significantly perturb the SPV and promote prolonged blocking (this has been shown in some extended model runs).
Based on the two significant pattern drivers noted here, I do expect a pretty quick change into a favorable (perhaps highly favorable) pattern for winter weather around Christmas week. There will likely be a period of time where the cold air dumps into the W US, but it should leak over as it usually does. The one wild card is if the MJO wave is interfered with. If this is the case, there could be some prolonged ridging over the E US as the western trough remains in place. However, I really don't buy it here.
Generally, based on the composites shown, the MJO will have more of a positive impact on the EPO domain (and some Greenland blocking influence), and the Scandinavian ridge will have much more of an impact on the NAO domain. It's certainly nice to see all of these pattern drivers move forward and become stronger in time, and it shows that the pieces will likely be in place to shake things up. Therefore, I do expect some insanely warm weather over the next week, but I have the impression that it'll snap the other way to close out the month.
