If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Hillsdale: 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 29°F. The snowiest months in Hillsdale are January, March, November, and December, with each month seeing an average of 10 inches of snowfall.