You'll likely spend much of your trip indoors, but if you're planning to venture beyond the casino, looking at local weather trends is a good idea. The hottest months are usually July and August with an average temp of 60°F, while the coldest months are December and January with an average of 20°F. The snowiest months in Sun Valley are February, January, March, and December, with each month seeing an average of 16 inches of snowfall.