Colder air will invade the storm in the Northeast bringing heavy snow in upstate New York and a change to snow in other parts of the mid-Atlantic and New England Wednesday into Thursday.
A surge of warmer air and heavy rain will continue to push northward through New England and into New Brunswick and Nova Scotia into Wednesday.
Meanwhile, the slow movement of the storm will allow cold air to catch up with lingering moisture farther to the southwest in the Northeastern states Wednesday into Thursday.
Portions of the northern tier of Pennsylvania, central and northern upstate New York and southern Quebec could receive 6-12 inches (15-30 cm) of snow with locally higher amounts through Thursday.
The worst travel conditions will be along Interstate-81 north of Scranton Pennsylvania to the Canada border and the I-90 portion of the New York Thruway, from Utica to Rochester.
In part of this area, the weight of the snow can bring down some tree limbs and cause sporadic power outages.
Occasional snow is forecast in parts of central and southeastern Pennsylvania, as well as western New England as the colder air is drawn into the storm Wednesday into Thursday.
Just enough snow can fall in the swath from the interior mid-Atlantic to western New England to coat grassy and elevated surfaces. Roads that became wet in these areas during the first part of the storm can become slippery at times as a result.
Snow and ice that changed to rain in northern New England will change back to intermittent snow on Thursday with an additional accumulation possible.
Intermittent snow or flurries can survive the trip to the Interstate-95 corridor Wednesday into Thursday, including Philadelphia and New York City, with the aid of gusty northwest winds.
The touch of snow can reach the northern and western suburbs of Baltimore and Washington, D.C. Snow showers are unlikely to return to southeastern New England for the duration of the storm.
Accumulating snow is in the offing for parts of West Virginia, western Maryland and western Pennsylvania as moisture on the back end of the storm is enhanced by the eastern Great Lakes and squeezed out over the higher terrain.
After a temperature dip into the end of the week, the mercury will trend back to average levels this weekend, then above average for much of next week. Typical highs during the middle of December are generally in the middle to upper 30s over the central Appalachians and the middle 40s in the I-95 corridor.