The very cold weather pattern of the past several weeks is on its way out of town for a while as some significant changes to the upper air pattern across North America are now underway. Gone is the strong ridge near the west coast of North America which has been blocking any flow of milder Pacific air into the interior of the continent. Also gone is the persistent polar vortex that has been swirling about through central and eastern Canada so far this winter.
We are left with a jet stream flow moving in a west to east motion across southern Canada and the northern U.S. allowing Pacific air to flood eastward pushing arctic air back to the northern reaches of Canada. The weakened polar vortex is expected to take a vacation in the area of the northwest islands of Canada and through the southern Arctic Ocean during the next week and maybe a bit longer.
Causes for the decided changes of our weather can be tied to the weakening of some of the blocking high latitude high pressure areas near the North Pole and through the Gulf of Alaska. These changes have allowed the jet stream to start to move into the British Columbia coast and to allow the polar vortex to lift back northward to a little more normal location.
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The resulting arrival of Pacific air across the Prairies during the coming days and a storm track to the north of the region will send temperatures skyrocketing as strong Chinook or Foehn winds develop. Gusty west winds will downslope off of the Canadian Rockies bringing temperatures above and even much above normal to many areas as we move through the next week.
This type of weather pattern generally is a dry one for the Prairies with most of the Pacific moisture being shed on the west side of the mountains. The Pacific winds then rise over the Rockies and downslope into Alberta and Saskatchewan where mild, dry weather occurs. Manitoba also benefits with the warming trend but not quite as much as areas further to the west. Some polar air influence can keep temperatures a little closer to average across the eastern Prairies in a pattern like we are expecting next week.
One of the adverse effects of the upcoming weather pattern is the potential of strong and damaging Chinook winds at times. Not only can temperatures rise quickly, but strong winds can damage property and even have been known to blow cars off the roads and derail trains.
As for how long the midwinter warming spell may last we think that there is potential that a good part of the next two weeks may be mild. Thereafter there are some signals that begin to show cooling temperatures but not to levels that we have had to endure during the past several weeks. As long as the strong west coast ridge and polar vortex combination do not return we probably will not see any extreme cold. That does not mean that further down the road in February that more cold weather could return to the region. In fact, one of the U.S. monthly computer models does show a return of rather cold weather several weeks from now, so don't put away the ear muffs just yet.
Doug Webster can be reached at firstname.lastname@example.org
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