Climate of Edmonton

Edmonton has a humid continental climate (Köppen climate classification Dfb).^[1] It falls into the NRC 4a Plant Hardiness Zone.^[2]

The city is known for having cold but sunny winters.^[3] Its average daily temperatures range from a low of −10.3 °C (13.5 °F) in January to a summer peak of 18.1 °C (64.6 °F) in July.^[4] The average maximum is 23.5 °C (74.3 °F) in July, and the average minimum is −14.7 °C (5.5 °F) in January.^[4] Temperatures can exceed 30.0 °C (86.0 °F) for an average of four to five days anytime from late April to mid-September and fall below −20.0 °C (−4.0 °F) for an average of 24.6 days. On June 30, 2021, at approximately 5:00 pm Edmonton South Campus reached a temperature of 37.4 °C (99.3 °F). This surpasses the previous 37.2 °C (99.0 °F) set on June 29, 1937.^[5][6] On July 2, 2013, a record high humidex of 44 was recorded, due to an unusually humid day with a temperature of 33.9 °C (93.0 °F).^[7][8] The lowest overall temperature ever recorded in Edmonton was −49.4 °C (−56.9 °F), on January 19 and 21, 1886 and February 3, 1893.^[9]

Summer lasts from late June until early September, and the humidity is seldom uncomfortably high. Winter lasts from November to March and in common with all of Alberta^[10] varies greatly in length and severity. Spring and autumn are both short and highly variable. Edmonton's growing season is from May 9 to September 22;^[4][11] Edmonton averages 135–140 frost-free days a year.^[4][12] At the summer solstice, Edmonton receives 17 hours and three minutes of daylight, with an hour and 46 minutes of civil twilight.^[13] On average Edmonton receives 2,299 hours of bright sunshine^[14] per year and is one of Canada's sunniest cities.^[4]

The summer of 2006 was a particularly hot one for Edmonton, as temperatures reached 29 °C (84 °F) or higher more than 20 times from mid-May to early September.

Edmonton's geography is also capable of producing summers where temperatures do not exceed 29.0 °C (84.2 °F). In Edmonton City Centre, the summer of 1916 had the lowest yearly maximum temperature of 27.2 °C (81.0 °F), and most recently in summer 1999 with a yearly maximum temperature of 28.8 °C (83.8 °F).^[15] Edmonton International Airport saw its lowest yearly maximum temperature at 28.3 °C (82.9 °F) in the summer of 1974.^[16] Summer 1980 and 1993 saw no daily minimum above 12.8 °C (55.0 °F) at Edmonton International Airport.^[16] The lowest yearly maximum daily minimum at Edmonton City Centre is 13.3 °C (55.9 °F), which was set and tied 5 times between 1883 and the last instance set in 1907.^[15] Summer 1992 also saw no dew point above 16.5 °C (61.7 °F) in Edmonton International Airport and 15.4 °C (59.7 °F) in Edmonton City Centre.^[15][16]

The winter of 2011–12 was particularly gentle. From December 22, 2011, till March 20, 2012, on 53 occasions Edmonton saw temperatures at or above 0.0 °C (32.0 °F) at the City Centre Airport.^{[17][18][19][20]}

The winter of 1969 was particularly cold. Between January 7 and February 1, temperatures at Edmonton's Industrial Airport reached daily highs of −6 °F (−21.1 °C) on two occasions and lows ranged from −14 °F (−25.6 °C) to −39 °F (−39.4 °C). The city's daily newspaper, Edmonton Journal, issued certificates for residents who lived through 'Edmonton's record cold spell'.

Edmonton has a fairly dry climate. On average, it receives 476.9 millimetres (18.78 in) of precipitation, of which 365.7 millimetres (14.40 in) is rain and 111.2 millimetres (4.38 in) is the melt from 123.5 centimetres (48.6 in) of snowfall per annum.^[4] Precipitation is heaviest in the late spring, summer, and early autumn. The wettest month is July, while the driest months are February, March, October, and November.^[4] In July the mean precipitation is 91.7 mm (3.61 in).^[4] Dry spells are not uncommon and may occur at any time of the year. Extremes do occur, such as the 114 mm (4.49 in) of rainfall that fell on July 31, 1953.^[4] Summer thunderstorms can be frequent and occasionally severe enough to produce large hail, damaging winds, funnel clouds, and occasionally tornadoes.

Twelve tornadoes had been recorded in Edmonton between 1890 and 1989,^[21] and eight since 1990.^[22] A F4 tornado that struck Edmonton on July 31, 1987, killing 27, was unusual in many respects, including severity, duration, damage, and casualties.^{[citation needed][23][24]} It is commonly referred to as Black Friday due both to its aberrant characteristics and the emotional shock it generated.^[25] Then-mayor Laurence Decore cited the community's response to the tornado as evidence that Edmonton was a "city of champions," which later became an unofficial slogan of the city.^[26][27]

A massive cluster of thunderstorms occurred on July 11, 2004, with large hail and over 100 mm (4 in) of rain reported within the space of an hour in many places.^[28] This "1-in-200 year event" flooded major intersections and underpasses and damaged both residential and commercial properties. The storm caused extensive damage to West Edmonton Mall; a small glass section of the roof collapsed under the weight of the rainwater, causing water to drain onto the mall's indoor ice rink. As a result, the mall was evacuated as a precautionary measure.^[29]