Taking into account the local weather in Alliston is an important factor for planning your visit, especially if you plan to spend your trip poolside. The hottest months are usually August and July with an average temp of 63°F, while the coldest months are February and January with an average of 26°F. The snowiest months in Alliston are February, January, March, and April, with each month seeing an average of 25 inches of snowfall.