Winter may officially start in December, but typically late fall and early winter is fairly mild when compared to January and February. So, why is that?
In most seasons, the arctic air takes a little time to gather strength (coldness) at the poles. With that said, the cold air at the poleward regions is weaker in the shoulder seasons, and gains strength as winter continues.
Often when these cold air pockets break off and get sent south by the jet stream, it’s referred to as the “Polar Vortex.” The below image, courtesy of the National Weather Service sums up this term well:
However you term the cold air – Polar Vortex, Canadian High Pressure, or something else – it’s all part of living in the continental interior of North America, and a common experience during the brutal winter months!