Overnight weather models continue to struggle regarding what happens late this week. Cold air will be spreading out across the Eastern United States with 2 waves of low pressure developing on the boundary between the cold air to the north and the warmer air to the south. The key driver in all this is the cold air and the northern jet stream. Weather models continue to show the battle between 2 streams. The north and the south continue to wage war on which one is going to be more dominant. It is a delicate balance between the two. The north has to be strong enough to bring down cold air (which it is) but if it is too strong it squashes the system in the south until it is well offshore.
You can see on the maps below the difference that occurs at the surface with the more dynamic look of the 0z GFS run verses the more suppressed look of the 6z run...READ MORE AT http://www.meteorologistjoecioffi.com/index.php/2017/01/02/snow-threats-hinge-cold-air-suppression/