Calgary experiences a humid continental climate within eastern parts of the city and a subarctic climate within western parts of the city due to an increase in elevation. The city has warm summers and freezing, dry, but like all of Alberta extremely variable winters. It falls into the NRC Plant Hardiness Zone 4a.
According to Environment Canada, average daily temperatures in Calgary range from 16.5 °C (61.7 °F) in July to −7.1 °C (19.2 °F) in January.
Winters are cold and the air temperature can drop to or below −20 °C (−4 °F) on average of 22 days of the year and −30 °C (−22 °F) on average of 3.7 days of the year, but 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, and may last several days. As well, Calgary’s proximity to the Rocky Mountains 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 summer, daytime temperatures range from 10 to 25 °C (50 to 77 °F) and exceed 30 °C (86 °F) an average of 5.1 days in June, July, and August, and occasionally as late as September or as early as May, and in winter drop below or at −30 °C (−22 °F) 3.7 days of the year. As a consequence of Calgary’s high elevation and aridity, summer evenings tend to cool off, with monthly average low temperatures below 10 °C (50 °F) throughout the summer months.
Calgary has the most sunny days year round of Canada’s 100 largest cities, with just 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 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.
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.
The highest temperature ever recorded in Calgary was 36.7 °C (98.1 °F) on August 10, 2018. The coldest temperature ever recorded was −45.0 °C (−49.0 °F) on February 4, 1893.