The persistent cold pattern that has covered much of Canada during the past few weeks is showing some signs of breaking down a bit. Temperatures are now moving into a pattern of variable if not highly variable readings as arctic air and Pacific air start to play tag across the region.
The reasons behind these changes are tied to a weakening of the polar vortex that has been across west-central Canada during recent weeks a shift of this feature to northeastern Canada. The strong ridge across the eastern Pacific northward to Alaska has also de-amplified to the west coast of Canada which allows for a better chance of some Pacific air making it into western Canada for brief periods.
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When a milder day occurs don't get used to it because in a pattern like this above freezing temperatures one day can be followed by readings below -20C the next. Precipitation prospects for a pattern such as this are generally light with the greatest chances coming behind arctic fronts when upslope winds have a better chance of developing.
The best chance of mild weather at times will be across Alberta during the next week or two while Manitoba might be the region seeing more dominant arctic cold.
Some of the computer model output is showing a January featuring milder than normal for a large portion of central and western Canada. Confidence is this pattern is low since the overall ridge/trough pattern across North America has not changed much recently. It will take only a little strengthening of the polar vortex and ridge to again bring more persistent cold to the Prairies during the next few weeks. Only time will tell if bitter cold returns for January or if chinnook winds take the bite out of the arctic cold.
Doug Webster can be reached at firstname.lastname@example.org
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