If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in Fond du Lac: 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 24°F. The snowiest months in Fond du Lac are January, April, February, and December, with each month seeing an average of 9 inches of snowfall.