In mountainous areas most live in the valleys and often hike in the mountains – normally a colder environment as you gain elevation. However in winter, often a surface temperature inversion will form in these areas as cold air, in contrast to the norm of temperature decreasing several degrees for every 1000 feet gained, remains trapped in the valleys, and often along with the any air pollution that may exist.
Inversions are likely to happen during periods with long winter nights, calm