Weird Post-Christmas Winter Hot Spell To Embrace Most Of North America. But It Might Not Last Long

Forecast map via Tropical Tidbits showing most
of North America with temperatures above normal
roughly a week from now.  The map shows
how far temperatures would be above or
below normal for this time of year. They'd
be farthest above normal near Hudson Bay,
but since it's winter, those "warm" temperatures
would only be in the 20s and 30s.

 We're heading into the depths of winter in North America, but you wouldn't know it given the Christmas Week forecast for almost the whole continent.  

Normally, large sections of the vast land mass would be colder than average for the season while other big areas would be having mild spells. 

By mid to late week, the only areas that will be chiller than usual for the end of December are Alaska and a small adjacent piece of northwest Canada.  Western Mexico might also be on the cool side, but not by much. 

Virtually all of Canada, from the British Columbian coast to Labrador, and from the southern tip of Ontario all the way north to Nunavut in the Arctic will be warmer than average.

Same is true coast to coast in the Continental U.S., except for maybe a small spot in California's Central Valley.

Now, it's winter, so nobody will be exactly hot. A few record highs are possible during this weird spell, especially in areas of Canada roughly near Hudson Bay, and then down toward the Great Lakes. 

For instance, in northwestern Quebec, near the shores of Hudson Bay, normal highs this time of year and in the teens to near 20 below Fahrenheit.  By the end of the week, those places will be in the mid 20s to low 30s above zero Fahrenheit, which is impressively balmy for this time of year. 

I'll want to oversimplify this, but is a forecast
showing the overall air flow in North America
in the last days of December. Follow the green
lines, You seen they come off the Pacific'then curl
north into eastern Canada. That blocks any cold
air in far north from coning toward the U.S. Red
hatched lines in Canada depict an upper air 
pattern that strongly favors warmer 
than average temperatures.

But the impressive thing is how huge this area of above normal temperatures will be, especially for this time of year.

The reason for this is a massive flow of mild Pacific air flowing into North America from the west.  Additionally, there's a massive northward bulge in the jet stream beginning to form. It's centered in central and eastern Canada, and by the end of the week will be enormous. 

That warm Pacific Ocean air will be forced to move both eastward across the United States, and northward through central and eventually into northeastern Canada - way the hell up there. 

This arrangement is pushing the usual pools of frigid air far to the northwest, centering it north of Alaska. Plus, this cold pool looks like it's smaller in size and weaker than you'd usually see in the winter. 

Usually, this cold pool is much stronger, and often extends across much of the northern half of Canada, and often centers itself near or not far from Hudson Bay. When that happens, the usual, occasional bursts of Arctic air can easily flow into southern Canada and the eastern two thirds of the United States.

As long as this weird weather pattern holds in place, there will be no more cold air to be had in eastern North America for awhile, at least after a zone of frigid air over southern Quebec and the northeastern U.S. gets out of here within a few days.

Don't expect this balmy North American winter to last forever. In fact it probably won't last all that long.  

It appears one of the more likely scenarios is that the big northward bulge in the jet stream over Canada might split in two, with one northward bump to the east, and the other in western Canada. That would create a southward dip in the jet stream between the two. That southward dip would allow cold Arctic air to eventually spill into south-central Canada and at least parts of the United States. 

If I had to guess, this would start happening a few day into the New Year.  NOAA's three to four week outlook, issued Friday and covering the period January 4 to 17, pretty strongly predicts below normal temperatures for most of the eastern two thirds of the United States.  The cooling trend in New England might (or might not!) wait until a couple or few days after January 4.