Oymyakon, Siberia managed to hit -76 degrees Fahrenheit twice in December, a temperature that had been reached only one other time in the last 25 years. The generation of such extreme cold air originates with the lack of sunlight far northern latitudes receive this time of year, which means they radiate heat to space without any solar energy offsetting that infrared cooling.
Water vapor content in the air also plays a role in the creation of extremely cold air. Contrary to what many people think, cold air does not become dry because it is cold, but instead air becomes cold because it is dry. The reason air can get so dry is because it has been slowly sinking from high in the atmosphere, where very little water vapor is present.
The constant shifting of air masses in the northern hemisphere usually keeps any one region from experiencing the extreme cold for more than a week or two.