If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Dexter: The hottest months are usually July and August with an average temp of 64°F, while the coldest months are January and February with an average of 23°F. The snowiest months in Dexter are March, January, April, and December, with each month seeing an average of 22 inches of snowfall.