Weather will likely play an important role when you plan your trip to Cornwall, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually July and August with an average temp of 65°F, while the coldest months are January and February with an average of 23°F. The snowiest months in Cornwall are January, March, February, and December, with each month seeing an average of 8 inches of snowfall.