I think that we will begin to see a transition to colder for the last few days of november into the first week of december with nothing extremely cold yet, Keep that in mind. I do not see a storm suddenly shifting the pattern to frigid before a snap back to more seasonal values. I think that the change will be gradual and the process going on now will set us up for an exciting winter pattern come december. Once we get into the favourable pattern, things will become very interesting with cold and snow storms but keep in mind it is still november and winter has not started yet. For week one of december i see near to slightly below normal temps across the eastern two thirds of canada. A key change by week 2 is the strong ULL in the Gulf of Alaska will have broken down already leading to more troughiness over the bering straits and a strong ridge over the GOA. This will lower the heights across the eastern part of the u.s as well as ontario and quebec. This will be the same case across eastern asia. Due to the strong blocking ridge that is forecast to develop in this time period across greenland the PV will shift south eastwards and allow the arctic air to plunge SE for weeks 2-4 of december.
Keep in mind though that if you live in atlantic canada you will be influenced by this ridge and will not experience as extreme negative departures. Part of this shift will be due to the warmest anomalies in the pacific setting up in nino 3.4 and 4 which is a cold signal across eastern NA. Also we are seeing a warmer then normal stratosphere centred across the eastern us and east asia. This will promote s strong trough across these regions and allow a ridge to form across greenland, alaska and the north pole because of cold stratospheric temps here. So it is the favourable ENSO setup, stratospheric setup and above normal snowfall that will allow the arctic air masses bottled up in NW canada to drop SE.
Because of the regeneration of the El Nino we are seeing a much stronger subtropical jet which will allow storm systems to move into the south central states undercutting the eastern trough and create the opportunities for snowstorms in mid to late december. This winter may be the one to make up for the lousy winters we have been having lately. Things look drastically different from last winter as a complete reversal may be taking place. This are looking up my friends, just be patient.