Climate of Calgary
Calgary has a semi-monsoonal humid continental climate (Koppen: Dwb, Trewartha: Dclo bordering Dcbo), with warm, wet summers summers and cold, dry, but highly variable winters. The city has an average temperature range from 16.9 °C (62.4 °F) in July to −7.6 °C (18.3 °F) in January. Average temperatures in Springbank Airport (slightly west of Calgary) range from 15.3 °C (59.5 °F) in July to −8.4 °C (16.9 °F) in January. The record high temperature is 36.7 °C (98.1 °F), held on August 10, 2018, and the record low temperature is −45.0 °C (−49.0 °F), held on February 4, 1893. However, in recent years, due to climate change, yearly low temperatures usually hover between −25 °C (−13 °F) and −36 °C (−33 °F).
Winters are cold, and the air temperature drops to or below −20 °C (−4 °F) for 22 days of the year on average, and as low as −30 °C (−22 °F) for 3.7 days of the year on average. These temperatures are frequently broken up by warm, dry chinook winds that blow into Alberta over the mountains. These winds can raise the winter temperature by 20 °C (36 °F), and as much as 30 °C (54 °F) in just a few hours, which may last several days. Calgary's proximity to the Rocky Mountains also affects winter temperatures with a mixture of lows and highs, and tends to result in a mild winter for a city in the Prairie Provinces. Temperatures are also affected by the wind chill factor; Calgary's average wind speed is 14.2 km/h (8.8 mph), one of the highest in Canadian cities. In the summer, daytime temperatures range from 10 to 25 °C (50 to 77 °F) and exceed 30 °C (86 °F) for an average of 5.1 days in June, July, and August, and occasionally as late as September or as early as May. As a consequence of Calgary's high elevation and aridity, summer days are often not humid, unlike many other major cities in Canada. Summer evenings also tend to cool off, with monthly average low temperatures reaching 9 to 10 °C (48 to 50 °F) throughout the summer months.
The wettest month is June with an average precipitation of 112.7 millimetres (4.44 in), while the driest month is January with an average precipitation of 10.0 millimetres (0.39 in). Calgary International Airport in the northeastern section of the city receives an average of 418.8 mm (16.49 in) of precipitation annually, with 326.4 mm (12.85 in) of that occurring in the form of rain, and 128.8 cm (50.7 in) as snow. The most rainfall occurs in June and the most snowfall in March. Calgary has also recorded snow every month of the year. It last snowed in July on July 15, 1999. The relatively low amount of precipitation in Calgary, when compared to other cities like Toronto, Vancouver, and Montreal, also gives Calgary a climate close to a cool semi-arid climate (Koppen: BSk, Trewartha: BSlo bordering Bsbo).
Thunderstorms can be frequent and sometimes severe, with most of them occurring in the summer months. Calgary lies within Alberta's Hailstorm Alley and is prone to damaging hailstorms every few years. A hailstorm that struck Calgary on September 7, 1991, was one of the most destructive natural disasters in Canadian history, with over $400 million in damage. Being west of the dry line on most occasions, tornadoes are rare in the region.
Calgary has the sunniest days year-round of Canada's 100 largest cities, with slightly over 332 days of sun; it has on average 2,396 hours of sunshine annually, with an average relative humidity of 55% in the winter and 45% in the summer (15:00 MST).
Calgary falls into the NRC Plant Hardiness Zone 4a and USDA zone 4b, as unlike NRC zones, USDA zones are solely based on low temperature. The average low temperature for Calgary is −31.5 °C (−24.7 °F), which would fall under USDA zone 4b.
Calgary has a short growing season, lasting 115 days between May 23 and September 15 on average.
On November 15, 2021, Calgary City Council voted to declare a climate emergency. A climate emergency declaration is a resolution passed by a governing body such as a city council. It puts the local government on record in support of emergency action to respond to climate change and recognizes the pace and scale of action needed.