Three important cold air sources for the central and eastern US in the winter season include Canada, Greenland and Siberia and two of these areas have had quite an impressive increase in snowpack in recent weeks and the third is about to receive widespread accumulations. As the snowpack builds up in these particular areas this time of year, cold air masses are very likely to follow as the nights grow longer going into winter season.
Canada, Greenland and Siberia
The overall weather pattern for the next couple of weeks is looking quite cold for much of Canada. Some of this cold air will drop into the Northern Plains over the next several days, but the Mid-Atlantic region will likely have to wait until late next week for a noticeable impact. Meanwhile, as the cold persists throughout Canada, there is likely to be quite a buildup of snow over the next ten days and this could have consequences around here over the next couple of months as this land mass is an important source of cold air for the central and eastern US.
Greenland is not always thought of as an important wintertime source of cold air for the central and eastern US, but it certainly can be given certain upper-atmospheric conditions. The accumulation of snow and ice on Greenland for the past year or so has been quite impressive with amounts at the high end of normal or even at record levels throughout much of that time period. Indeed, the snow/ice pack on Greenland continues to be at very high levels relative-to-normal as we head towards the winter season.
Finally, Siberia is probably thought of even less than Greenland in terms of an important cold air source for the Mid-Atlantic; however, there are indeed air masses that cross over the North Pole and drop southward through Canada and into the northern US. In fact, some of these type of air masses are known for their extreme cold in this part of the world. Research studies have shown that the increase of snowpack in the region of Siberia south of 60 deg N can be an important early indicator of the potential for “high-latitude blocking” events during the subsequent winter season (Meteorologist Dr. Judah Cohen, AER).
If the snowpack increases dramatically during October in this region and to above-normal levels then that has been found to be a useful predictor of more frequent “high-latitude blocking” events during the subsequent winter season which often lead to sustained cold air outbreaks for the central and eastern US. In fact, snow has increased quite noticeably across Siberia between October 1st and October 31st, but quite as much as in some recent years. There is more detailed information on the “high-latitude blocking” phenomenon and prospects for it this winter in the “2017-2018 Winter Outlook by Vencore Weather”.
One final note, snowpack throughout the Northern Hemisphere at the end of September was clearly in above-normal territory as it has been during the past few years.
Meteorologist Paul Dorian
Video discussion on the buildup of snow around the northern hemisphere: