The next cold temperature issue arises in the week-3 forecast when all “weeklies” models project an evolving upper trough in the East U.S. ECM continues with the strongest trough forecast. For the moment, arctic air is not anticipated with this upper trough.

The mega-cluster ensemble, combining ECM and GFS, projects “most likely” temperature anomaly scenarios for early January cooling off the U.S. to near normal while Canada stays warm. The most likely candidate for colder than normal temperatures is the Interior West and possibly Western Canada.

Typical of climate pattern(s) nowadays, regional SSTA are influencing local climate in unexpected ways. The best recent example is the cooling of the western North Atlantic basin initiated by north-turning tropical cyclones during the late warm season. The low-pressure area off the U.S. East Coast has invited surprising chill to the East U.S. as meteorological winter begins.

Ahead of a strong cold front, a squall line featuring possible severe thunderstorms, a rarity for December, moves from the Northern Mid-Atlantic States early this afternoon across southern New England this evening. Locally heavy rain causing flooding high wind, and severe thunderstorms are possible.