If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Barrie: The hottest months are usually July and August, with an average temperature of 18°C, while the coldest months are February and January, with an average of -4°C. The snowiest months in Barrie are March, December, January and February, with each month seeing an average of 38 cm of snowfall.