Montreal is classified as a warm-summer humid continental climate in the Montréal-Trudeau airport and a hot-summer humid continental climate (Köppen climate classification: Dfa) at McGill University.
Summers are warm to hot and humid with a daily maximum average of 26 to 27 °C (79 to 81 °F) in July; temperatures in excess of 30 °C (86 °F) are common. Conversely, cold fronts can bring crisp, drier and windy weather in the early and later parts of summer.
Winter brings cold, snowy, windy, and, at times, icy weather, with a daily average ranging from −10.5 to −9 °C (13.1 to 15.8 °F) in January. However, some winter days rise above freezing, allowing for rain on an average of 4 days in January and February each. Usually, snow covering some or all bare ground lasts on average from the first or second week of December until the last week of March. While the air temperature does not fall below −30 °C (−22 °F) every year, the wind chill often makes the temperature feel this low to exposed skin.
Spring and fall are pleasantly mild but prone to drastic temperature changes; spring even more so than fall. Late season heat waves as well as “Indian summers” are possible. Early and late season snow storms can occur in November and March, and more rarely in April. Montreal is generally snow free from late April to late October. However, snow can fall in early to mid-October as well as early to mid-May on rare occasions.
The lowest temperature in Environment Canada’s books was −37.8 °C (−36 °F) on January 15, 1957, and the highest temperature was 37.6 °C (99.7 °F) on August 1, 1975, both at Dorval International Airport.
Before modern weather record keeping (which dates back to 1871 for McGill), a minimum temperature almost 5 degrees lower was recorded at 7 a.m. on January 10, 1859, where it registered at −42 °C (−44 °F).
Annual precipitation is around 1,000 mm (39 in), including an average of about 210 cm (83 in) of snowfall, which occurs from November through March. Thunderstorms are common in the period beginning in late spring through summer to early fall; additionally, tropical storms or their remnants can cause heavy rains and gales. Montreal averages 2,050 hours of sunshine annually, with summer being the sunniest season, though slightly wetter than the others in terms of total precipitation—mostly from thunderstorms.