If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Henniker: The hottest months are usually July and August with an average temp of 67°F, while the coldest months are January and February with an average of 27°F. The snowiest months in Henniker are January, March, February, and November, with each month seeing an average of 10 inches of snowfall.