Multi-day heat wave to grip Central Ontario. Here’s how to beat the 45 humidex

Centennial Beach in Barrie, Ont in the 2026 summer. (CTV News/Luke Simard)

A multi-day heat wave is set to grip central Ontario starting today, with Environment Canada issuing a yellow heat warning as temperatures climb to “potentially dangerous levels.”

The national weather agency says daytime highs will range from 30 C to 37 C, while overnight temperatures will sit between 20 C and 24 C, offering little relief from the heat.

Humidex values to skyrocket

Humidex values could reach 38 to 45, with Tuesday expected to be one of the hottest days of the weather event.

This warning covers Barrie, Innisfil, Orillia, Midland, Collingwood, Newmarket, Caledon and several surrounding areas.

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Environment Canada says prolonged heat can affect everyone’s health, especially older adults, young children, people with chronic illnesses, those who work or exercise outdoors and anyone who does not have access to air conditioning.

Here’s how you can prepare

Residents are encouraged to drink plenty of water, limit outdoor activity during the hottest part of the day, wear lightweight clothing and check in regularly on family members and others who may be vulnerable.

Environment Canada also says that the hot, humid conditions could lead to deteriorating air quality, with the Air Quality Health Index potentially reaching the “high-risk category” in some communities.

This heat warning is expected to remain in effect until at least Wednesday evening or Thursday, says weather experts.

Environment Canada advises everyone to stay alert for signs of heat exhaustion or heat stroke, which is a medical emergency.

When heat becomes a medical emergency

If you experience any of these symptoms during extreme heat, health officials advise you to move to a cool place and drink liquids right away.

Symptoms of heat exhaustion:

• Headache
• Nausea or vomiting
• Dizziness or fainting
• Rapid breathing and heartbeat
• Extreme thirst (dry mouth or sticky saliva)
• Decreased urination with unusually dark yellow urine
• Changes of behaviour in children (like sleepiness or temper tantrums)

Did you know? The Ontario government notes that sunburned skin loses its sweating efficiency. This makes it harder for your body to regulate its temperature.