There was an unusual ice storm about 100 miles north of where I live the day before Christmas. My younger daughter, 150 miles south, reported flooding from torrential rains and mid-60F temperature 3 days before Christmas. From what I've read over the past few years, the jet stream is becoming more erratic.
During the winter here, there used to be a pattern. Early in the winter, cold air would move in for about 3 days, go away for 3, and then return, ever colder. By January, the cold dips would be the worst, and last at least a week. The description I read was that during the summer, the jet stream had between 3 and 5 "waves," or "lobes," circling the globe. As the weather grew colder, the lobes begin to bulge larger, and move down from the polar region. By mid- winter, the lobes gathered into perhaps just one very larger wave that could extend from west to east coast of NoAm, and as far south as the Gulf of Mexico.
Now, the jet stream is breaking up, and instead of flowing like a river around the world, it is turning into eddies that move north and south rapidly and un-predictably. Instead of cold air gradually replacing warm air, there are much more rapid shifts, meaning that precipitation levels go way up.
The day before Christmas, our morning temp. was 4F. Tomorrow is predicted to be 48F.