How are heat warnings triggered in Canada?


Over the winter I produced a map showing the thresholds for triggering snowfall warnings in Canada, but now that summer is in full swing, it’s time to do the same for heat.

Environment Canada issued a “special weather statement” for southern British Columbia over the weekend because the temperature was expected to reach 30 to 40 degrees Celsius, but they issued no statement for the Cariboo region of the province even though the forecast was also calling for temperatures in the mid-30s.


My friends in Quesnel and Williams Lake were feeling left out, as they should. The above map gives the false impression that temperature was going to be cooler in the Cariboo than Vancouver and Cranbrook (Williams Lake and Quesnel were 34°C while Cranbrook was 31°C).

But that aside, Environment Canada has set different thresholds across the country for triggering a heat warning, and in addition, they can use their discretion to add warnings in special circumstances — say if it’s the first heat wave of the summer. In this case, they issued a “special weather statement” which is not the same thing as a “warning.” They do not issue heat warnings for most of BC for some reason even if the forecast was calling for 500°C. I guess they figure we’re tough, and can handle it.

Ignoring the fact that places like Cranbrook were never forecast to reach 35°C, it looks likely the red area was generated on account of being the first heat wave of the year. Don’t ask me why Williams Lake didn’t get included in the statement even though it was over 35°C in the valley bottom (the airport 1,000 feet above the city was 34°C).

Environment Canada defines 13 different sets of criteria for triggering a heat warning in Canada. Some make sense, but others should be revised. Why bother listing a threshold for Nunavut when it never gets remotely close to the trigger point (40°C) while not listing one for southern British Columbia where most summers exceed 40°C?

Perhaps the silliest of all is the convoluted criteria set for Vancouver and the South Coast. It takes the average of today’s 2pm temperature at the Vancouver or Abbotsford airports and tomorrow’s forecast high to determine if a warning is warranted. Surely, there’s a better way to trigger a warning!


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3 Responses to How are heat warnings triggered in Canada?

  1. Pingback: Rainfall Warning Thresholds in Canada | Questioning The Data

  2. Pingback: What Does it Take to Trigger an Extreme Cold Alert in Canada? | Questioning The Data

  3. Pingback: It’s so Hot in Canada that the Northwest Territories is Under a Heat Warning for the First Time EVER! | Questioning The Data

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