Many times each year, especially in late fall, winter, and early spring, many valleys of northern and western Utah experience temperature inversions. Inversions occur when air near the ground radiates (or loses) heat to space during the nighttime hours. As a result, warmer, lighter air rises and rests on top of the cold, heavier air, creating stable and stagnant weather conditions in lower elevations. These inversions are caused by the existence of a cold surface high pressure system (called "The Great Basin High") and warm high pressure conditions aloft. When these inversions last beyond a few days they can reach 2,000 feet above the valley floor and produce pollution and extensive fog in the valleys. This effect is more pronounced when there is considerable snowcover in the valleys.
Much of the information for this section originally appeared in the copyrighted book Utah's Weather and Climate, edited by Dan Pope and Clayton Brough, in 1996. UCCW Directors have received permission from the copyright owners of this book to reproduce such information on its website and to revise and updated it where appropriate.