Extreme heat

A heat wave or conditions of extreme heat occur when temperatures hit 32 degrees Celsius or higher, for three or more days in a row. These extreme hot weather events can lead to:

  • Increased humidity
  • Health concerns
  • Poor air quality or smog, which is the result of heat combined with air pollutants from industry, gas-powered vehicles, and other sources


Humidex values measure how hot the weather feels to the average person. Under normal conditions, your body produces sweat that evaporates to cool you down. Under extreme heat, the body must work harder to maintain its normal temperature. A humidex advisory is issued when humidex values are expected to reach 40 or more. The higher the humidex, the harder it is for your body to cool itself.

Smog alerts

Smog levels indicate and forecast the current air quality information. Most smog days in Ontario occur between May and September. When an alert is issued, avoid strenuous physical outdoor activities. If you have a heart or lung condition, consult your family doctor on how to keep healthy in the heat.

How to stay safe during extreme heat

  • Check local weather forecasts for updates
  • Check that your air conditioner is in working condition
  • Find places to cool down in your area
  • Check on your family or friends who are isolated and may be living alone
  • Ensure you have a backup generator
  • Stay hydrated by drinking plenty of water
  • Wear loose fitting clothes and hats to protect from direct sunlight
  • Keep your home cool by closing curtains and blinds during the day
  • Visit a city swimming pool, air-conditioned libraries, spray pads and community centres (call ahead because hours of operation may vary)
  • Take cold showers or baths, or go to an air conditioned public space
  • Avoid outdoor work and intense outdoor exercise in the heat or humidity
  • Never leave people or pets inside parked vehicles
  • Use fans to increase air circulation

For more information on extreme heat alerts and how to stay cool, refer to the Peel Region.