If you're hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Williston: The hottest months are usually July and August with an average temp of 68°F, while the coldest months are January and February with an average of 19°F. The snowiest months in Williston are March, October, April, and February, with each month seeing an average of 9 inches of snowfall.