Weather is probably a major factor when you plan your trip to Sillian, 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 54°F, while the coldest months are January and December with an average of 24°F. The snowiest months in Sillian are February, January, March, and December, with each month seeing an average of 137 inches of snowfall.