If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Grangeville: The hottest months are usually August and July with an average temp of 65°F, while the coldest months are December and January with an average of 31°F. The snowiest months in Grangeville are February, January, April, and October, with each month seeing an average of 6 inches of snowfall.