On average, there are 191 sunny days per year in West Yellowstone. Average daytime temperatures vary from 28°F (−2°C) in January to 84.5°F (29.2°C) in July. Heavy snowstorms may occur as early as September or as late as May, though most snow falls from November to March. Throughout the state, summer nights are generally cool and pleasant. It’s best to pack a sweater and light jacket, as the difference between morning and evening temperature could be vast.