Preword: Before reading on, please disregard all past calls for a favorable pattern change and good December in recent days. Those prospects are not likely now.
I was one of the first to call for it, and now am one of many beginning to rethink calls for a pattern change. In fact, I'm outright canceling any of my hopes of a more favorable pattern after mid December, and here's why.
That high pressure system over the Bering Sea kind of acts as if you had a piece of string being held up by two vertical structures. This Bering sea ridge of high pressure is one of these 'vertical structures', and the other one is off the Canadian Maritimes. The middle of the 'string' holds the cold and snow, and because those two 'vertical structures' are in place, this 'string' cannot move south and deliver winter-like weather to the States.
Many were calling for a big pattern change around Mid December which would supposedly get us into the real winter pattern we were waiting for and had been denied of last year. Well, here's the new pattern.
But we have another problem-- the Pacific North American index, or the PNA index.
The PNA's territory is off the West Coast and in the Northeast Pacific. In short, whatever weather happens in the West US, the opposite is observed in the East. So, if we saw a ridge of high pressure in the West, the PNA would be positive and the East would see cool and stormy weather. The negative PNA gives the storms to the West and the warmth to the East.
And just like that, the East gets the short end of the stick, while the West benefits greatly, especially in skiing resorts.
In case anyone's wondering, the North Atlantic Oscillation (NAO) stays neutral-ish around this forecast period, not really benefitting anyone and not trying to demolish the negative PNA.
What this means for the East is that we will still see very unseasonably warm temperatures, off and on. Thanks to the cold and storms now favoring the Rockies, it is probable that these systems will push east and give the rest of the nation a break from warm weather before it gets going again. The polar vortex (a.k.a. the Arctic Oscillation (AO)) looks to be stronger than normal, and you know what that means- enhanced probabilities of warm weather, nationwide.