There is no question that a major storm is going to develop Wednesday night & Thursday along the Atlantic seaboard. All the models have it. The upper air supports it. The impacts on our weather are obvious on the Arctic cold in that it will bring the worst of it Friday and Saturday. Saturday morning in particular will be the coldest day of this stretch that began back on Christmas. We will see much of our area from Eastern Pennsylvania to New Jersey & Southern New England at or below zero Saturday morning. Even Friday morning will be brutal with lows in the single digits to below zero. How cold will depend on any additional snow cover and that is the big question that is left to be answered.
The European upper air jet stream shows the forecast problem. It would be easy if we had a full phased upper trough but we don't. Instead we have a ton of northern energy interacting with separate features from the southern half of the jet stream. It appears that the upper trough energizes the coastal low offshore and keeps it well offshore. Normally this would be a no brainer. Storm well offshore means no snow with the low far out to the east. However the issue remains complicated. The northern upper trough seems to hang back on the European model which develops and pulls precipitation back unusually far to the west. This idea also shows up on the Canadian model and to a lesser extent the GFS model...READ MORE AT http://www.meteorologistjoecioffi.com/index.php/2017/12/31/major-atlantic-storm-thursday-offshore-impacts-arctic-air/