Many residents of the U.S. have had to deal with record-setting frigid temperatures and dangerous wind chills lately but that is about to change during Christmas week and beyond.
December has featured two significant plunges of polar air, with the coldest one beginning late last week and extending through the weekend. On December 17th, Bismarck, North Dakota, set a daily record with a low temperature of -30 degrees. The wind chill temperature dove down to a ridiculous -48 degrees. On Sunday, Sioux Falls, South Dakota, tied a daily record with -26 degrees and a wind chill temperature of -35ºF.
NFL players and fans had to withstand temperatures barely above zero in Chicago (for the Bears vs. Packers game) while conditions weren’t much better in Kansas City for the (Chiefs vs. Titans game) with temperatures around 10 degrees.
As far south as Dallas, Texas, the temperature plunged to a frigid 18 degrees early Sunday morning with a wind chill around 0ºF.
Weather Pattern for the Final Week of December 2016
During the month of November, some very cold air built up in the higher latitudes on the other side of the globe, especially in Siberia. The cold expanded into across the pole and into North America in early December as a large ridge of high pressure (bulge in the jet stream) spread northward from the North Pacific and Alaska to westernmost Canada.
Conversely, there was a trough of low pressure (dip in the jet stream) into the central U.S. This allowed some very cold air to plunge southward. Since the origin of this air mass was over land and frozen water to the north, it’s defined as “continental polar air”. Because, there is no large high pressure ridge on the east side of North America, this air mass is not locked in place so conditions can change rather rapidly. This will be the case as we move toward Christmas and beyond.
Upcoming December pattern
As we progress through the week, the jet stream pattern aloft will change rapidly and so will the temperatures across most of the nation. As the ridge of high pressure aloft breaks down, the jet stream pattern will flatten out and be more oriented from west to east across the nation. The prevailing air mass with be from the North Pacific Ocean, while the polar air retreats northward into Canada.
Although the North Pacific is chilly, it’s not nearly as cold as the frozen land masses and ice to the north. This intrusion of what’s defined as “maritime polar” air into the nation will set the stage for generally milder temperatures as we move toward Christmas and likely beyond. The coldest temperatures, and best chance for any wintry precipitation will be confined to areas closer to the Canadian border and in the higher elevations of the West. The threat of thunderstorms in the Plains will also increase as we head to the weekend.
Holiday travelers will probably like the temperatures by the end of the week. This will lead into a very mild Christmas Day for many of you.
The latest computer model guidance suggests that this milder temperature pattern is likely be to around for awhile.