Historic Heat Wave Comes to an End

A cold front passed through the Winnipeg area early this morning between 6 and 7 am, ending what was an historic heat wave across the southern Prairies. The heat started last Monday (Aug 6) in the western Prairies and last Tuesday (Aug 7) in the Eastern Prairies. However, the peak of the heat occurred from Thursday through Sunday (Aug 9 to 12), and moved from west to east. The heat wave was the result of an upper-level ridge of high pressure over the western US which expanded northward into Canada for several days, spreading a hot and dry air mass into the region. However, by Sunday, humidity also became part of the equation in the Eastern Prairies as south-southeasterly winds pumped in moisture from the US Midwest. 

The remainder of this post will go through the peak of the heat day-to-day from Friday through Sunday. Note that hotspots for Alberta and Saskatchewan are only from ECCC stations, while in Manitoba, both ECCC and Mb Ag stations are considered.

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Friday August 10

Hotspots

Alberta	Saskatchewan	Manitoba
40.8°C Barnwell	40.1°C Maple Creek and Assiniboia	36.0°C Waskada and Boissevain

On Friday (Aug 10), the heat peaked in southern Alberta and southwestern Saskatchewan with highs between 36 and 41°C. Southern Manitoba reached highs between 31 and 36°C. Multiple all-time records were broken for both the month of August and all-time, in southwestern Saskatchewan and Alberta. 

Calgary (YYC) reached 36.5°C, the hottest temperature ever recorded at the Calgary Airport since records began in 1881, beating the old record of 36.1°C in 1919 and 1933. It was also the hottest temperature in August, beating the old record of 35.6°C in 1914. As a result of the heat, ENMAX Power reported that the city reached an all-time record for electricity demand. 

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Saturday August 11

Hotspots

Alberta	Saskatchewan	Manitoba
35.1°C Spondin	42.3°C Moose Jaw	39.7°C Alonsa

The peak of the heat moved into southern Saskatchewan and southwestern Manitoba on Saturday. Widespread highs above 40C occurred from the US border northward to Regina and Moose Jaw. Temperatures rose very quickly in the morning as well, with temperatures of 38C in the Assiniboia and Yellow Grass areas already by 11 am CST. By noon CST, it had already reached 40.4°C in Yellow Grass. 

Moose Jaw reached a record 42.3°C, the 2nd hottest day ever recorded in the city since 1894. It was also the highest temperature recorded in Canada (ECCC weather station network) since 2007, when Woodrow, SK reached 43.0°C. Regina reached 41.3°C, the 3rd hottest day ever recorded in the city since 1884. It also beat the old all-time record for August of 40.6°C in 1949. Lastly, it was the latest date in the year that Regina hit 40°C, the previous latest being August 6, 1949. 

It was a very dry Las-Vegas-style heat in Saskatchewan as well. Relative humidity dipped to 9% at Regina Airport (YQR), the lowest on record since 1953. The previous record was 10% in 1959 and 1961. 

In Alberta, the cold front moved through Friday night into Saturday, with hot temperatures confined to the extreme southeastern corner of the province on Saturday. 

Winnipeg reached 37.1°C, the hottest day since August 23, 2011 (37.2°C). It also broke the old record of 34.9°C in 1978. 

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Sunday August 12

Hotspots

Alberta	Saskatchewan	Manitoba
29.0°C Masinasin	38.6°C Estevan	40.0°C Elm Creek and Waskada

On Sunday, the peak of the heat moved into southern Manitoba and was also still in the extreme southeastern corner of Saskatchewan. Widespread highs between 35 and 40°C occurred throughout southern Manitoba. As mentioned previously, humidity was also high with dewpoints reaching the low to mid 20s. The humidity gradually decreased through the day due to boundary layer mixing, first in southwestern Manitoba south of Brandon then in the Red River Valley by late afternoon. 

In Deloraine, the temperature had already reached 33°C at 10 am CDT and 35°C at 11 am CDT. Down sloping wind off the Turtle Mountains helped this localized region heat up much more quickly than its surroundings however. By the end of the day, Waskada and Elm Creek were the only locations that hit 40°C with highs of 40.0°C.

In Winnipeg, the high of 37.5°C was the hottest since June 17, 1995 (37.8°C). It also broke the daily record of 35.0°C in 1972 and it was the 9th hottest August day on record since 1873. This was only the third time since 1872 that the city exceeded 37°C two or more days in a row - the last time being in August 1949, and the only other time being in July 1936. In addition, the last time the Airport exceeded 35°C two days in a row was in June 1995. 

Humidex reached 45.0 at Winnipeg Airport (YWG), the third highest humidex value in August since 1953:

Highest humidex values in August since 1953 at Winnipeg Airport (YWG):

45.5 Aug 4, 2001

45.1 Aug 13, 1965

45.0 Aug 12, 2018

44.4 Aug 4, 1983

Brandon had a humidex of 44.4, the second highest humidex value in August since 1958:

Highest humidex values in August since 1958 at Brandon Airport (YBR):

46.2 Aug 4, 2001

44.4 Aug 17, 1995 and Aug 12, 2018

43.5 Aug 22, 1969

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In Winnipeg, the three-day period from Aug 10 to 12 exceeded 32.0°C, officially making it a heat wave (according to the older version of the ECCC weather glossary). This was the first official heat wave at the Airport since a four-day heat wave in August 2013 (Aug 25-28). Note that this definition of a heat wave is not widely agreed on in Canada. The most recent version of the ECCC weather glossary does not even define a heat wave. 

According to Rob's Obs, it was also the 3rd hottest weekend on record in Winnipeg since 1872.

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If you would like more information or statistics (such as emphasis on other cities), please contact Weatherlogics or post a comment under this post. This post and the information contained in it is subject to copyright. Copies or dissemination, in whole or in part, is not permitted without permission from the author.