Canada's heat warning colour system explained
Environment Canada uses yellow, orange, and red alerts; Toronto is under orange as temperatures feel like 40 C.
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With a heat dome stifling large swaths of Canada, millions are living under yellow and orange heat alerts issued by Environment Canada. To help the public understand the severity of warnings, the agency introduced a colour-coded system on November 26, 2025.
The colour system—yellow, orange, then red—helps emergency services and agencies quickly assess the severity and likely impact of extreme weather. Environment Canada issues heat warnings 18 to 24 hours before an extreme heat event when daily temperatures will reach heat warning thresholds for two or more days in a row with no relief overnight. Single-day heat events do not trigger warnings.
Yellow represents the most common alert. Impacts are "moderate, localized and/or short-term" and may cause damage, disruption, or health impacts including increased illness or death risk, brownouts, power outages, workforce impacts, and outdoor event delays. A yellow heat warning typically involves elevated daytime and overnight temperatures for just a couple of days, according to meteorologist Ross Hull at Global News.
Orange alerts are less common and issued when severe weather is "likely to cause significant damage, disruption, or health impacts." Impacts are "major" and "widespread," potentially lasting several days. Orange heat alerts can bring higher illness and death risk, travel disruption, water shortages, power outages, crop damage, and widespread impacts on essential services and outdoor events. "A red heat warning would indicate taking it to even another level," Hull said. "You're talking more than three days."
Red alerts are rare, with impacts described as "extensive, widespread, and prolonged." Red heat warnings signal "very dangerous and possibly life-threatening weather" that "will cause extreme damage and disruption."
