Weather will likely play an important role when you plan your trip to Smiths Falls, 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 66°F, while the coldest months are January and February with an average of 25°F. The snowiest months in Smiths Falls are January, February, December, and November, with each month seeing an average of 18 inches of snowfall.