The well-advertised El Nino across the tropical Pacific is in a strong phase as we move toward the end of October and is expected to peak before the end of 2015. History from previous strong El Ninos show they can have a big influence on the weather and climate of Western Canada.
As we have already seen during early and mid-fall, mild weather has had the upper hand across Western Canada due to the dominance of Pacific origin air masses. Periods of cooler weather have been mostly brief in nature or without too much vigor since the machine that helps produce very cold weather across northwest and northern Canada has been largely disrupted.
The attached charts show today's NOAA temperature outlook for November across North America and what stands out is the nearly full coverage of orange and red colors which denote above-normal temperatures forecasts. This chart is very close to what we expect to see for temperature departures during the cold season across North America during a well-established El Nino.
Temperatures are expected to average more than 2 degrees Celsius above normal across the western Prairies and more than 3 degrees C above normal across the eastern Prairies next month. It is important to note that while the monthly average is most likely to be above normal, there are also mostly likely to be a few short periods of colder weather intertwined; however, these colder periods should be short and without the extreme chill that the past few winters have presented.
The main reason for the minimal amount of cold weather for Western Canada is the lack of high pressure development across northwest Canada. This happens because the main jet stream tends to roll in from the Pacific in a west-to-east fashion and without the buckle into a ridge that we saw during the past two years. One part of Canada that can see a little more cold is across far eastern and northeastern regions which are where there is a better opportunity for a mean trough or at times a polar vortex to develop.
As winter continues, we will likely see cooler-than-average weather develop across the southern United States. Past strong El Ninos show this cooler regime expanding to cover the southern half of the U.S. by early spring, while Canada tends to remain quite mild through the entire period.
Doug Webster can be reached at firstname.lastname@example.org
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