December Thaw: Long-Lasting Break From Arctic Chill For Most

http://www.weather.com/forecast/national/news/december-thaw-major-warming-trend

After several rounds of arctic chill this fall, most of the country will enjoy a long spell of warmer-than-average weather over the next week or two -- just as meteorological winter has begun.

 

A jet stream pattern that has encouraged cold air masses from near the Arctic Circle to rush southward into the U.S. will change over the next several days, allowing much milder air from the Pacific Ocean and Gulf of Mexico to become the dominant influences on temperatures nationwide.
Computer forecast models are in strong agreement that this will allow unseasonably warm weather to take over a large part of the Lower 48 later this week and on into next week.