The upper air flow across North America has shifted enough during the past week or so to allow for much more seasonable temperatures to encompass Western Canada. In some cases, temperatures have even fallen somewhat below normal, helped along by the snow cover, long nights and high pressure which has promoted radiational cooling.
Radiational cooling is common across northern latitudes during the winter when snow cover is common and nights are long. When skies are clear and winds are light or calm, any warmth near the surface quickly escapes to space. This process works better with snow cover and is especially efficient with fresh, fluffy snow.
If you're not fond of the recent colder spell of weather, then you may not have to wait too long for a return of mild conditions as we still have a strong El Nino in place across the tropical Pacific ocean. The current spell of colder weather has been created by a southward shift in the location of the polar jet stream in response to a strong ridge through the western Atlantic Ocean.
It appears that the strong ridge far to our southeast and the trough across Western Canada and the western U.S. will last into early next week before both features flatten out to allow the polar jet stream to move in a west-to-east fashion once again. The polar jet stream is also expected to lift northward into Western Canada again, allowing a return of the Pacific flow that warmed the region during November and through the first half of December.
It comes as no surprise that we should see a return of mild conditions around or shortly after the new year begins, since the probability of warm weather during a strong El Nino is very high for much of western and central Canada. Attached is a forecast for January 6 to 12, and Jan. 13 to Jan. 19, for North America. These were released today for North America, and were produced by the National Centers for Environmental Prediction in the U.S.
As you can see, widespread warmth is again forecast for western and central Canada into the north-central U.S. with only the far northeast portion of Canada seeing any chill. These temperature forecast depictions are very close to what typically has been observed during past strong El Ninos.
With a strong El Nino like we are seeing through the Pacific, we are pretty confident that periods of colder weather, as we are seeing now, will be short-lived this winter and that the warmer pattern that appears to be returning soon are more of the norm.
Doug Webster can be reached at firstname.lastname@example.org
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