I have long been talking about the lack of arctic air so far this winter, despite having a weak polar vortex, which has the tendency to allow arctic air southward through the mid-latitudes. We have not seen arctic air in any real significant stretch thus far in the United States. Eastern Russia, on the other hand, has been where the arctic air has lurked over the last four-to-six weeks.
The pattern may be changing to allow more of a "winter" feel into the eastern half of the United States starting late next week.
First, the southern jet stream has been quite active during the last few months. Its activity has been producing substantial precipitation over much of the U.S. over the past month. This has included significant winter storms for the Southern and Central Plains to the Northeast. This jet stream is expected to become a little less active next week.
Second, the weak polar jet stream looks to take over and a blocking pattern will take shape next week as a ridge develops over the West Coast and a deep trough sets up east of the Rocky Mountains. At first, there will not be an arctic connection with just a couple of storms moving through the country.
However, models are hinting at the arctic air making an intrusion to at least the northern half of the country and especially southern Canada late next week. With the polar jet steam continuing to be forecast weaker than normal, this blocking pattern may lead to better drainage of arctic air southward from Canada through the end of the month.
Despite the snow that came to the Central and Southern Plains and Midwest last week, there is little snow cover over winter wheat areas. With warm weather next week ahead of the arctic intrusion, significant snow cover is not expected. We will not know the true depth of the cold air intrusion until maybe as late as this weekend, but the potential extreme cold could come with winterkill opportunities.
This may be more likely over the Midwest than for the Central and Southern Plains, but there is ample time for that to change in the models. A slight shift westward in the upper level trough will allow the cold air to slide south along the spine of the Rockies.
I should mention that not all models are on board with the arctic intrusion. The American GFS model and its model ensemble is anticipating this arctic intrusion much more than the European model or its ensembles, as of the evening runs on Jan. 4.
However, there are hints of it in some of the European's model members of its ensemble of this possibility. Instead, the European extended model waits one more week before bringing in the arctic air. Both models extend much of this cold air through the Plains and western half of the Midwest well into February. An extended winter chill is looking more likely to move from Russia to North America. The question now is the extent and duration.
John Baranick can be reached at email@example.com
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