Fog is a cloud that is close to the ground. It forms when air near the ground cools and water vapor in the air condenses into tiny but visible water droplets. Fog tends to form first in the lower areas and along and over bodies of water such as the Great Salt Lake and Utah Lake. In January 1931, Salt Lake City logged a record 21 days of dense fog which reduced visibility to one-quarter mile or less. In January of 1985 and again in 1992, 16 days of dense fog were recorded in Salt Lake City.
In Salt Lake City, November through February are considered the "fog months." Since 1948, there have been an average of 12 days of heavy fog in this four-month period. By month, the average number of heavy fog days are: one day in November, four days each in December and January, and three days in February.
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.