John Wheeler: Arctic air has well-known characteristics
When Arctic air is driven southward, its frigidity is usually tempered by conditions along the way.
FARGO — When the forecast calls for Arctic air, most people immediately know what is coming. By definition, Arctic air is not just any cold air. It is air which has come to us directly from the Arctic. Specifically, this refers to air from approximately 66.6 degrees North latitude, which is about 1,000 miles north of the Canadian border and roughly 1,350 miles north of I-90. At this latitude, there is barely any daylight for most of the winter. With so little solar radiation, this air gets very cold.
When Arctic air is driven southward, its frigidity is usually tempered by conditions along the way. The speed at which it gets here and the amount of air mixing in from other regions determine its temperature once it arrives. Other important factors are snow cover and sky conditions. If Arctic air travels here under a clear sky and over deep snow it will have been warmed less by either solar or terrestrial infrared radiation.