The coldest day of winter in the Northeast is projected for Saturday. During the afternoon, the 12Z GFS indicates temperatures not reaching 10F in Boston while wind chill is routinely 10-15F below zero (during the afternoon). The Sunday morning low temperatures are near zero in Boston. The Boston heating degree day for Saturday is probably around 60 with an effective HDD of 70-75.

A sizeable change in the Pacific North America (PNA) index is forecast by all models over the next 2 weeks. The persistent strong positive phase fueling the warm and dry West U.S. climate for much of January finally breaks down. Next week, the PNA pattern shifts to negative phase supportive of a cooler and wetter West U.S. low-pressure trough pattern. In response, the strengthening negative North Atlantic oscillation (-NAO), fueling East U.S. cold fades mid-month likely causing a cold retreat.

In South America, several weather hazards are indicated in the GFS 10-day precipitation outlook. Developing heavy rains last through the next 10 days east of Paraguay to the Southeast Brazil Coast. Meanwhile, Northern Argentina is dry and extremely hot through 10 days. The exception is an area of heavy thunderstorms in Central Argentina during the 6-10-day period.

Well-documented is the cold influence on North America and Eurasia climate by an ongoing intense negative arctic oscillation (-AO). Additionally, -AO has inspired a vigorous Southern Europe storm track most recently associated with Winter Storm “Kristin” and effects on Portugal and Spain. -AO continues well into February maintaining the energetic Southern Europe storm track.