If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Jamesburg: The hottest months are usually July and August with an average temp of 73°F, while the coldest months are January and February with an average of 37°F. The snowiest months in Jamesburg are February, January, March, and April, with each month seeing an average of 5 inches of snowfall.