A heat wave is usually defined as a period of 3 or more consecutive days with temperatures of 32° C or higher. High HUMIDITY is not a requisite, yet most, but not the worst, heat waves are oppressively humid. By these criteria St John's and Vancouver have never experienced a heat wave, and Victoria has had only one, lasting 4 days in 1941.
The frequency of hot spells increases inland. Periods of up to 5 successive hot days have been recorded in every province from BC to NS. The BC interior usually records the most protracted heat waves - as long as 30 days. Across the southern Prairies and in southern Ontario, hot spells can last 10-15 days. Other places experience heat waves of only 3 to 5 days.
The most memorable heat waves occurred during the DROUGHTS and dust storms on the prairies in the 1930s. Other notable heat waves were in August 1944 in the Maritimes, August 1953 in Ontario, July 1963 in Québec and August 1981 in southern BC.
The 1936 heat wave originated in the southwestern US and was continent-wide. Heat records that were set in 16 states still stand. The heat wave penetrated Canada during the first week of July. In southern Saskatchewan and Manitoba, the hottest period ran 13 days from the 5th to the 17th, and in Ontario the spell lasted 8 days, beginning over northwestern Ontario on the 7th and ending across the province on the 14th. In Manitoba, temperatures reached 44.4° C at St Albans on the 11th and at Emerson on the 12th, the hottest days ever recorded in the province. In Winnipeg, temperatures topped 32° C on 13 consecutive days and peaked at 42.2° C on the 11th. That night it "cooled" to 28.3° C.
In Ontario, a new provincial high temperature of 42.2° C was set at Atikokan on the 11th and 12th and repeated at Fort Frances on the 13th. At Toronto, the heat wave was its most intense on record for observations going back nearly a century. A peak of 41.1° C was recorded on the 10th and the "highest low" occurred early on the morning of the 11th, 26.6° C.
The 1936 heat wave killed 780 Canadians - 376 males and 404 females, most of whom were elderly and infants. A year earlier there were only 42 heat-related deaths. In July 1936, there were another 400 indirect casualties including several drownings. Ontario had the greatest number of deaths - nearly 600 persons - and in Toronto over 225 succumbed to the heat. Heat-related deaths in Manitoba exceeded 70.