**This post is dedicated to those who lost their lives in the tragic massacre in Connecticut. All information below is typed and published in honor of the children and teachers killed in this horrible event.**
The image above is composed of these two models' 8-10 day 500mb height anomaly forecasts. In areas of blue, a stormier pattern is likely to develop. Oranges and reds indicate a warmer and quieter pattern should develop. This is the pattern in the few days before Christmas.
The ECMWF model on the left shows a strong west-based negative NAO developing in the near future. If we have a negative NAO, the tendency for storms and cold weather to hit New England is increased. In a west-based negative NAO, a specific enhancement is placed on these two categories for the general East Coast. If you want to know how we determine a west-based negative NAO, it is literally the negative NAO signature (high pressure system over Greenland) being west of Greenland. In an east-based negative NAO, that ridge is east of Greenland and the Plains/Midwest get in on the cold and snow.
Also intriguing is the ECMWF's push for a slight positive PNA, as the persistent low pressure pattern causing our current, unfavorable negative Pacific-North American (PNA) index phase moves further offshore. The development of low pressure in the East forces high pressure to tend to develop in the Rockies, and suddenly we have the Pacific working in our favor. I would say to watch out for that deep high pressure system in the north Pacific, but if a piece of the polar vortex sticks itself in the Bering Sea, we don't have much to be concerned about in that aspect.
Speaking of the Polar Vortex (PV), notice how we see no strong low pressure anomalies in the Arctic. That's GOOD! What that means is the polar vortex is weak, and when you have a weak polar vortex, you have cold air trying to make a push south. If it were to move south, I have a good feeling it would enter the North Plains and get pulled south as a strong storm system makes its way across the central and east parts of the nation.
Lastly, and one of the more important items of interest is the intense meridional flow we will see if this solution evolves as forecasted by the ECMWF. Meridional flow, for those of you unfamiliar with the term is when the jet stream aligns in a more north-south pattern, rather than just west-east. When you have storms moving through areas of meridional flow, the spin in the energy, called vorticity, is enhanced. As a result, the storm system is strengthened. Ever wondered why storms are enhanced in negative NAO situations? Now you know.
In conclusion, the models seem to be latching onto a much better pattern (especially in the Pacific) for the last week or two of December. This favorable pattern could very well lead into January, where additional chances of more sustained cold are likely to be found. The areas that could be most affected by the new pattern include the Northeast first and foremost, with the Ohio Valley/Midwest/Plains likely to feel the effects as well.
Notice how I didn't mention the GFS here? It's because the GFS has been wobbling recently, and, when in doubt, seek comfort with those you trust (in my case, the ECMWF).