"At what temperature is cold weather considered 'arctic?' " This very good question came into the weather office this week. Actually, there is no temperature consideration at all.
"Arctic air" does not refer to a certain temperature. Rather, "Arctic air" is a reference to the source region of a mass of air.
Air that comes to us from near or north of the Arctic Circle is considered arctic. During winter, the weather that comes our way from these regions is extremely cold due to the lack of sunlight.
The cold air we endured from Christmas into early January was of Arctic origin. However, the cold weather of the recent past had been drifting around the northern Plains and Canadian prairie provinces for weeks and would not be considered "Arctic."
Air that comes our way from the Arctic Circle in spring is likely to be a lot less frigid than wintertime Arctic air, but would still be considered Arctic because of its origin.