If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in St. Johnsbury: The hottest months are usually July and August with an average temp of 63°F, while the coldest months are January and February with an average of 22°F. The snowiest months in St. Johnsbury are March, January, February, and November, with each month seeing an average of 15 inches of snowfall.