December Thaw: Long Warm Spell Likely for Much of Western, Central U.S. Through Mid-Month

A prolonged spell of unusually warm December weather is expected to cover a sizable swath of the U.S. in the week ahead, and even the occasional interruptions in the mild pattern won't be all that cold.
A jet stream pattern that has encouraged cold air masses from near the Arctic Circle to rush southward into the U.S. has changed, allowing much milder air from the Pacific Ocean and Gulf of Mexico to become the dominant influences on temperatures.
Computer forecast models are in strong agreement that this will allow unseasonably warm weather to take over a large part of the western and central U.S., not to mention a large swath of western and central Canada, for most of the upcoming week.
This means temperatures will stay well above freezing, day and night, across much of the Deep South this weekend through at least Tuesday.
Meanwhile, subzero lows and single-digit highs in the north-central states should give way to high temperatures at or above freezing at times, especially late in the week ahead.
 http://www.weather.com/forecast/national/news/december-thaw-major-warming-trend