Discussion: Forecast models are in good agreement on a cold spike striking the Northeast U.S. Thursday night/Friday morning and lasting through next weekend. The peak of cold is Friday morning through Saturday morning when very cold temperatures are accompanied by high wind producing extreme wind chill.
ECMWF projects temperatures dropping to 14F in Boston Friday morning (Fig. 1) with widespread singles numbers away from the coast and subzero for New York/Vermont with wind! Well below normal zero wind chill factors! Due to cold advection (strong cold wind) there is little temperature rise during the day on Friday as maximum temperatures fair to reach 20F and stay near 10F away from the coast (Fig. 2).
On Saturday morning Boston drops to 5F with 13F in New York City and Philadelphia (Fig. 3). Inland areas with snow cover are below zero. The wind is not quite as gusty but wind chill remains well below zero Saturday morning.
Saturday afternoon is not quite as cold or as windy as Friday afternoon. By Sunday temperatures begin to recover but remains below normal.
Fig. 1: ECMWF minimum temperature forecast for Friday morning.
Fig. 2: ECMWF maximum temperature forecast for Friday afternoon.
Fig. 3: ECMWF minimum temperature forecast for Saturday morning.