Saint-Firmin has an oceanic climate (Köppen climate classificationCfb). The average annual temperature in Saint-Firmin is 9.2 °C (48.6 °F). The average annual rainfall is 1,097.0 mm (43.19 in) with October as the wettest month. The temperatures are highest on average in July, at around 18.5 °C (65.3 °F), and lowest in January, at around 0.3 °C (32.5 °F). The highest temperature ever recorded in Saint-Firmin was 37.5 °C (99.5 °F) on 19 August 2012; the coldest temperature ever recorded was −23.5 °C (−10.3 °F) on 27 December 1962.
Climate data for Saint-Firmin (1981–2010 averages, extremes 1951−present)