It seems the cold spots have been in either Siberia or Europe over the past 5 years or so. The Pacific jet didn't help during those years, just scouring out any cooler air in Canada. This year, we saw some of the cold pockets actually come up and over the poles, down into eastern Canada. I don't know if there is actually a why? Almost like a roulette wheel, a game of chance where the cold air will drop into to? Of course it will follow the path of least resistance, which some can explain better than myself...