As has been depicted by many of our weather forecasting tools, we are seeing a strong period of high latitude blocking across Canada. This blocking pattern will peak later this weekend into early next week before weakening and by 10 days from now should be a distant memory.
When we speak of high latitude blocking, we are talking about an area of high pressure in the upper levels that builds northward into Greenland or northeast Canada and breaks up the polar vortex, forcing it southward from its normal home across northern Canada. When this happens, we normally see arctic cold displaced southward from when it normally would bring the big chill to southern Canada and the U.S.
This scenario is underway as we speak and during the next several days a piece of the polar vortex will move from eastern portions of the Northwest Territories southward through Manitoba and then on eastward across the northern Great Lakes and finally across southeastern Canada early to middle of next week. At the same time, a ridge through the western portion of the continent will allow for a large arctic high to develop across northwestern Canada which will slowly push southeastward across the Prairies by early next week and into the northern and northeastern U.S. by the middle of next week.
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The coldest weather of the season will accompany this arctic surge for most of interior Canada and the northern U.S. with below- to well-below-normal temperatures likely to visit the Prairies from this weekend into early next week. Thereafter, we are likely to see a moderation trend as the blocking pattern breaks down and arctic air loses its grip on Western Canada.
During the final week of January we expect to see the western North America ridge weaken allowing more of a westerly flow of Pacific-influenced air sending temperatures upward to normal and most likely to above-normal levels at times before the month is complete. Many of the same prediction tools that gave us notice of the cold wave now arriving are also showing the return of a much milder weather pattern later this month into February.
The accompanying forecast chart from the U.S. National Center for Environmental Prediction for February shows an impressively mild pattern once again for Canada as westerly winds aloft transport Pacific air eastward. This temperature pattern is quite consistent with an El Nino pattern which is still strongly in place.
Our fairly brief period of high latitude blocking has disrupted El Nino for Canada for the early and mid-part of January, but signs are pretty strong that mild conditions are going to make a return during the last week of January and for a good portion of February. As we have said all along, the potential fly in the ointment is whether we see a return of any high latitude blocking next month.
Most of our prediction tools show minimal threat of blocking at this time. We had about a two-week warning of our current cold outbreak so we should get some reasonable warning if another period of cold weather decides to invade western or central Canada during the second half of the winter.
Both the cold pattern of the next week and the milder one to follow are expected to feature less-than-average precipitation for the Prairies. This is also a consistent outcome for a strong El Nino weather pattern.
Doug Webster can be reached at email@example.com
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