Ag Weather Forum

The mild conditions observed across Canada during most of December are about to become a memory as upper level wind patterns are beginning to shift. The flow of modifying westerly Pacific winds is already beginning to wane and during the next several days a modest ridge will take shape across the Gulf of Alaska blocking the Pacific flow.

The polar vortex has either been cycling about near the North Pole or has been on the Asian side of the pole during most of December and has been weak. If our model projections are correct, changes are also coming for the pool of swirling high level winds as well.

Current indications are for the polar vortex to strengthen and slowly move southward to the Hudson Bay region by this time next week. The combination of the evolving polar vortex and ridge through the eastern Gulf of Alaska will create a cold air making pattern for a large portion of Canada next week. Arctic air which has been mostly absent during the past couple of weeks will return in a big way as surface high pressure builds across western Canada allowing for radiational cooling over the widespread snow cover.

Below and possibly well below normal temperatures may visit the Prairies before we are done with December. More cold weather may be in the works for the new year as well but there appears to be a difference with the expected upcoming pattern to that of last winter.

The persistent blocking we saw last winter led to the nearly endless cold for several months. This time around there appears to be minimal amounts of blocking and this may produce more of a cyclical temperature pattern for western Canada as we move into January. The location of the main polar vortex may be across northeastern Canada allowing for interruptions in the cold weather pattern.

Even if the more changeable temperature pattern is what we see during the next few weeks a significant return of winter weather is most definite for next week into early January. As for snow potential with the new pattern, more often than not we see a burst of light to moderate snow as cold air arrives and moves up against the mountains with the threat of major snowfall mostly limited.

With the expected limited high latitude blocking during the next few weeks, the door remains open for some warm spells as down sloping winds develop off of the Rockies. A weak El Nino also remains in place which favors milder weather for western Canada so even though the cold is coming in the short term, it probably will not be as persistent as last winter.

Doug Webster can be reached at doug.webster@dtn.com

(ES)

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