An active jet stream will continue to carry Pacific storms into the West Coast, and after a week of flooding the country with warm air, producing record warm temperatures in several cities for the month of December, this mild air will be offset by a deepening but broad trough that will allow cold air to seep southward from Canada. Near the Canadian border, this will mean cold air produces below normal temperatures in the Northern Plains and Upper Midwest. In the southern United States, the mild air will be well entrenched and too far from any Canadian push of cool, meaning above normal temperatures prevail. For a belt between, including the Northeast, near normal or perhaps very slightly above normal temperature should be the result.
Precipitation is a very difficult forecast in the Northeast. There are some regions that are obvious, like the northwest United States, where Pacific storms continue to slam into the coast. It does appear as though the Eastern slopes of the Rockies ignite with snow in an upslope event this period, to the delight of skiers. Meanwhile, it remains to be seen how two particular strong energetic disturbances behave in the Northeast - one around the 15th, another at the very end of the period. Both of these have the potential to tap moisture available in the Southeast United States, but it's quite tenuous at this point as to whether that moisture truly does phase with the northern stream energy. As such, I've opted for a near normal precipitation forecast for the Northeast.