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.
What do the alert colours represent?
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.
Yellow alert: What it represents
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.”
Below are potential outcomes from a heat wave classified as a yellow alert, according to Environment Canada:
- Increased risk of illness or death
- Brownouts and/or power outages
- Animals at risk
- Outdoor events delayed and/or adjusted
- Workforce impacts due to higher temperatures indoors and outdoors
“A yellow heat warning would be an elevated daytime and overnight temperature for just a couple of days,” Hull said.
Orange alert: What it represents
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:
- Higher risk of illness or death
- Localized travel disruption
- Risk of localized water shortages
- Brownouts and power outages
- Animals at higher risk
- Crops, plants and gardens at risk of damage
- Items, vehicles or materials left in direct sunlight are at risk of damage
- Some damage to critical infrastructure
- Outdoor events delayed and/or cancelled
- High impacts on essential services
Red alert: What it represents
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.”
A red alert for a heat event can result in the following, according to Environment Canada:
- Extreme risk of illness or death
- Widespread travel disruption due to route damage and/or aircraft, train, or vehicle performance
- Excess demand and potential damage to utilities, including energy and water
- Power outages and water shortages
- Animals at extreme risk
- Crops, plants, and gardens at risk of extreme damage
- Items, like vehicles or materials left in direct sunlight at risk of damage or destruction
- Damage to critical infrastructure
- Outdoor events delayed and/or cancelled for multiple days
- Prolonged, widespread impacts on essential services
What is the difference between weather warnings, advisories and watches?
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.
This story was originally published by Global News on June 30, 2026. CityAM Canada is republishing it for our Canadian readers.