Utah receives plenty of sunshine. On an annual basis, Salt Lake City receives 67% of all possible sunshine, averaging 125 clear days, 101 partly cloudy days, and 139 cloudy days a year. In comparison, Milford receives 70% of all possible sunshine, averaging 151 clear days, 103 partly cloudy days, and 111 cloudy days. Salt Lake City's sunniest month is July (with 83% possible sunshine), while Milford's brightest month is June (with 83% possible sunshine).
The average daily accumulation of solar energy generally increases the farther south one travels from the Utah-Idaho border. Average daily accumulations range from 400 langleys in the northern part of Utah, to about 500 langleys in the extreme southwestern part of the state. (A langley is a unit of radiant energy equal to one gram calorie per square centimeter.) The greatest energy accumulations occur during the summer months. Logan/USU averages about 670 langleys per day during July, and Salt Lake City about 690. South of Utah, Las Vegas, Nevada averages about 748 langleys in June. By contrast, the accumulations during the month of December are 275 langleys at Las Vegas, while in the northern portion of the state, Salt Lake City accumulates an average of only 154 langleys and Logan/USU 148 langleys.
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.