December has been warm so far across the U.S. but changes are on the way. A stratospheric warming event causing arctic air to generate in southern Canada coupled with a progressive Madden Julian oscillation to configure the upper air pattern supportive of delivering the cold to the U.S. is ahead. As always the degree of cold experienced in the U.S. will be dependent on snow cover. Most forecast models indicate a considerable expansion of snow cover over the next 2 weeks caused by upslope flow into the Rockies, lake-effect snows in the vicinity of the Great Lakes and an evolving storm track that could bring significant snow to the Northeast.
The incoming cold is not unprecedented in recent years. Interestingly, only 3 starts to a New Year (of the past 10) have been warmer than normal. Into early January 2018 is projected as the 3rd coldest of the past 10 years and very close to 2010. The coldest start to January in the past 10 years was in 2014, the second of 2 consecutive “polar vortex” winter seasons.
The Climate Impact Company 11-15 day forecast indicates the bold cold across the northern U.S. for late December into early January.
Pictured: The Climate Impact Company 11-15 day temperature anomaly outlook.