Some winters are easy on us with mild weather and not much snow, while others have a completely different theme featuring bitter cold and snow piles to tell your grandchildren about. So why can one year be so different than the next? In some cases, during one winter we can see a significant overhaul in a weather pattern during the same season.
The answer is not so easy to understand and most likely lies more in the category of theory than an etching in stone. Europe has endured four severely cold winters during the past 10 years, including a couple that even ranked in the top five coldest on record. During those same years, North America was pretty mild with moderating Pacific air more prevalent than arctic chill.
Winters can be so different partly because of the position of air that meteorologists call the polar vortex. This is a pool of very cold air up at 25,000 to 50,000 feet above the ground that is also like a large whirlpool of bitter cold air. The jet stream flows to the south of the polar vortex in general, and as waves within the jet stream pass along, a new surge of cold air is released southward behind the wave.
This is the part of the answer we know the most about. The part of the big answer as to why one year the polar vortex makes a home across northeast Europe or western Russia then the next year settles in across the Hudson Bay region of Canada is more in the theory category.
The key to our cold weather potential each winter lies in whether the polar vortex is on the Asian side of the pole or the North American side. This year it has been located across Canada much of the time and that's why Canada and the U.S. have been shivering so much during the recent weeks. Europe has seen a much more moderate winter temperature-wise so far due to the lack of the upper level cold whirlpool. There have been important wind and rain storms for Europe, however.
The reasons why the polar vortex likes one side of the pole one year versus the next are still unclear. The cold pattern we have been in actually got started last spring. A very cold spring was recorded across central and Western Canada fueled by high latitude blocking. It seems that weather has a memory as the polar vortex returned during the fall across Canada, this time due not so much to high latitude blocking but by a persistent ridge near the west coast of North America.
This ridge blocks the modifying influence of the Pacific across North America and allows cold air to quickly build up across the snow-covered land scape. The result is the type of winter we have endured to date with December temperatures averaging 3 to 7 degrees C (6 to 14 degrees F) below normal across the Prairies.
The model forecasts into January are telling us that the Prairies will see some moderation while central and Eastern Canada stay very cold. Experience tells me that as long as that pesky polar vortex and west coast ridge are still around that episodes of very cold weather can be expected for the Prairies, maybe not quite has harsh as we have seen during December, but still annoyingly cold.
Doug Webster can be reached at firstname.lastname@example.org
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