What Canada’s colour-coded heat warnings mean as temperatures soar

An extreme heat event is identified when daily temperatures reach heat warning thresholds for two or more days in a row with no relief overnight.

With a heat dome currently stifling Canada, many parts of the country are under heat warnings issued by Environment Canada.

According to Environment Canada, millions of Canadians are under yellow and orange alerts for heat, with advisories listed across Ontario, Quebec, Alberta, Saskatchewan and the Northwest Territories.

An extreme heat event is identified when daily temperatures reach heat warning thresholds for two or more days in a row with no relief overnight.

Environment Canada also states that the agency aims to issue heat warnings 18 to 24 hours in advance of an extreme heat event. If a stretch of heat is expected to last a single day, no warning will be sent out.

In addition, heat warnings are issued “when air temperature and/or humidex forecasts reach levels that could impact your health,” Environment Canada states. This is also dependent on different temperature values across Canada.

Environment and Climate Change Canada (ECCC) introduced the colour-coded weather alerts on Nov. 26, 2025, in an effort to “tell you at a glance what risks the weather may pose to you.”

The weather alert colours start at yellow and, as the potential risk increases, they change to orange, then red.

The change to the colour-coded system helps “more easily communicate the severity or the seriousness of particular weather events to agencies that need to know about it,” said Ross Hull, a meteorologist with Global News.

The yellow alert serves as the most common alert, according to the ECCC. The impacts of a yellow alert are “moderate, localized and/or short-term.”

In addition, the weather that is classified under a yellow alert “may cause damage, disruption, or health impacts.”

“A yellow heat warning would be an elevated daytime and overnight temperature for just a couple of days,” Hull said.

The ECCC states that the orange alert is more uncommon and is issued when severe weather is “likely to cause significant damage, disruption, or health impacts.”

Any weather event identified under an orange alert has the implications of being “major” and “widespread,” with the potential to last “a few days.”

An orange alert issued for a heat event can consist of the following happening, according to Environment Canada:

Red alerts are identified as rare, with impacts being “extensive, widespread, and prolonged,” according to Environment Canada.

The implications of a red alert are listed as “very dangerous and possibly life-threatening weather” that “will cause extreme damage and disruption.”

“A red heat warning would indicate taking it to even another level,” Hull said. “You’re talking even more than three days. This would be sort of likely a very rare type of situation where, say, we’d be an entire week or more of this type of stifling heat and humidity, and that can lead to, obviously, some serious health issues for people.” 

Environment Canada outlines that a watch is put out for Canadians to “get ready” for “potential severe weather” and is issued when “conditions are favourable for the development of severe weather.”

If conditions escalate, a watch can be elevated to a warning.

Hull said that an advisory “is usually not to a degree that obviously a watch is needed.”

Environment Canada issues an advisory when Canadians must “act now to protect yourself from significant weather” and it is typically issued for blowing snow, fog, freezing drizzle and frost.

For a watch to be declared, Hull said that conditions “are favourable for a certain event to happen.”

“There generally is not a heat watch, for instance. A watch is more for — if we’re gonna use the summer context — a severe thunderstorm watch. That’s what you’re going to see a lot of during the summer. That would mean that conditions are favourable for a particular area to see severe weather,” he said.

Environment Canada states that warnings are issued for Canadians to “act now to protect yourself from severe weather.” Warnings are usually issued six to 24 hours in advance but can be longer.

Severe weather, such as tornadoes, can be issued with less than 30 minutes’ notice.