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As parts of eastern Canada bake in 30+°C temperatures, there have been many questions on whether this is a true heat wave or not.

Is this an official heat wave or not? Experts explain


Andrea Bagley
Digital Reporter

Friday, August 12, 2016, 7:19 PM - As parts of eastern Canada bake in 30+°C temperatures once again, there have been many questions on whether this is a true heat wave or not.


SUMMER 2016: Visit the Summer Forecast Guide to the Season for the 2016 Summer Forecast, Fall Weather Preview and much more


"Up until several years ago, the general rule (for most provinces, but not all) was three or more consecutive days with temperatures 32°C or higher," says Weather Network meteorologist Dayna Vettese. "There is no longer an "official" definition of a heat wave."

According to Vettese, Environment Canada removed the definition and never reinstated one, so it remains open to interpretation.

"I think it’s still a good general theme to follow the previous criteria when it comes to heat waves, but it’s important to note that Canada is a very large country and what may be considered "hot" in southern Ontario will differ from what is considered "hot" in, say, Vancouver or St. John’s," Vettese adds.

The old criteria also differed across the country where Ontario was based on three consecutive days of 32+°C, but Quebec was based on 30°C, mainly due to differing climates in these regions.

How do heat warnings differ from a heat wave?

Environment Canada still issues heat warnings, which take into account dangerous, potentially life threatening heat.

"When a heat warning is issued, the public is being warned that the temperatures will be to a point where it could be dangerous. Whereas the term "heat wave" is generally used conversationally," explains Vettese.

Alerting parameters Environment Canada uses for issuing a Heat Warning:

Alert type Location Threshold criteria
Warning     Newfoundland and Labrador, New Brunswick, Nova Scotia and Prince Edward Island Issued when humidex value or temperature expected to reach 40 for at least one hour. 
Warning Quebec, except Nunavik

Issued when the humidex value is 40 or greater and when the temperatures is 30 degrees or warmer, and both conditions persist for at least one hour. 

Or

Issued when temperature is 40 degrees or greater. 

Warning Ontario - Extreme southwest (Essex and Chatham-Kent counties)

Issued when 2 consecutive days of daytime maximum temperatures are expected to reach 31 degrees or more and nighttime minimum temperatures are expected to fall to 21 degrees or more.

Or

Issued when 2 consecutive days of humidex values are expected to reach 42 or more. 

Warning Ontario - Remainder of southern Ontario (including Districts of Parry Sound and Nipissing) 

Issued when 2 consecutive days of daytime maximum temperatures are expected to reach 31 degrees or more and nighttime minimum temperatures are expected to fall to 20 degrees or more.

Or

Issued when 2 consecutive days of humidex values are expected to reach 40 or more. 

Warning Ontario - North

Issued when 2 consecutive days of daytime maximum temperatures are expected to reach 29 degrees or more and nighttime minimum temperatures are expected to fall to 16 degrees or more. 

Or

Issued when two consecutive days of humidex values are expected to reach 36 or more. 

Warning Saskatchewan, Manitoba, Northwest Territories and Nunavut Issued when humidex value or temperature expected to reach or exceed 40 degrees. 
Warning Alberta - Extreme south (including Pincher Creek, Cardston, Lethbridge, and Medicine Hat Issued when 2 consecutive days of daytime maximum temperatures are expected to reach 32 degrees or more and nighttime minimum temperatures are expected to fall to 15 degrees or higher. 
Warning Alberta - Remainder of Alberta Issued when 2 consecutive days of daytime maximum temperatures are expected to reach 29 degrees or more and nighttime minimum temperatures are expected to fall to 14 degrees or higher. 
Warning British Columbia - Vancouver Issued when the temperature is expected to reach 29 degrees or more on consecutive days.
Warning British Columbia - Abbotsford Issued when the temperature is expected to reach 34 degrees or more on consecutive days. 

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