After a mild autumn and warm start to December the climate pattern reverses much colder as a “polar vortex” regime evolves in 9-10 days lingering into middle December. Early season chill especially in the Midwest with widening/deepening snow cover is expected.

Negative North Atlantic oscillation unfolding and causing a series of pattern-changing cold troughs across Europe. The result is early season snow cover which is a surprise given the very warm autumn.

Pictured: The Climate Impact Company cold season 2017-18 U.S. heating degree day forecast. Climate discussion: The winter 2017-18 climate pattern is locking in. Here are the contributing factors.