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Heat Warnings


Learn about heat illnesses and how to take precautions and prevent health issues in extreme heat.


Many people look forward to enjoying the outdoors during the summer. While it is important to spend time outside, it is also important to remember the health problems extreme heat and humidity can cause.

What is a heat warning/extended heat warning and when is it issued?

Heat Warning

When forecast temperatures are expected to be at least 31°C and overnight temperatures are above 20°C for 2 days or the humidex is at least 40 for 2 days.

Extended Heat Warning

When forecast temperatures are expected to be at least 31°C and overnight temperatures are above 20°C for at least 3 days or humidex is at least 40 for at least 3 days.

What is humidex?

Humidex describes how hot, humid weather feels to the average person. This measurement is calculated using temperature and humidity readings.

Who is at greatest risk from extreme heat?

Extreme heat and humidity is a potential danger to us all. Factors such as obesity, dehydration, fever, infection, sunburn and alcohol abuse can increase a person's risk.

Those at greatest risk include:

  • Older adults (over the age of 65)
  • Infants and young children
  • People with chronic illness such as heart disease or asthma
  • People with physical or mental disabilities
  • People who work in the heat
  • People who exercise in the heat
  • People who have limited resources to protect themselves

What are heat illnesses?

When a person's body temperature rises quickly and sweating is not enough to cool the body, heat illness occurs. High body temperatures can lead to:

  • Heat stroke
  • Heat exhaustion
  • Fainting
  • Heat cramps (muscle cramps)
  • Heat rash
  • Heat edema (swelling of hands, feet and ankles)

What are symptoms of heat illness?

If you experience any of the following symptoms during extreme heat, immediately find a cool place and rehydrate by drinking liquids. Water is best.

  • dizziness or fainting
  • nausea or vomiting
  • headache
  • rapid breathing and heartbeat
  • extreme thirst
  • decreased urination with unusually dark yellow urine

How can I prevent heat illness?

  • Pay close attention to how you feel while outside in the heat
  • Visit neighbours, friends and older family members, especially those who are chronically ill, to make sure that they are staying cool and hydrated.
  • Plan outdoor activities during cooler parts of the day
  • Close awnings and curtains to block out the sun
  • Avoid sun exposure. Wear a wide-brimmed hat or use an umbrella.
  • Wear loose-fitting, light-coloured clothing made of breathable fabric
  • Drink plenty of cool liquids, especially water before you feel thirsty
  • Prepare meals that do not require cooking in the oven
  • Take a break from the heat and spend some time in a cool place
  • Use a fan to help stay cool
  • Take cool showers or baths
  • Never leave people or pets in a parked vehicle or in direct sunlight

Are there cooling centres in Halton?

In the event of a heat warning, there are a number of cooling centres and places for you to visit including swimming pools, splash pads and air-conditioned public facilities. Malls and movie theatres can be a good escape from the heat as well.

Visit your local municipal website for hours and locations.


What can I do to help prepare for extreme heat events?

  • Ensure air conditioners are working properly.
  • Ask your doctor or pharmacist if certain medications you may be taking can increase your health risk in the sun and heat.
  • Choose light-coloured paint for the exterior of your home.
  • Plant a broadleaf tree to provide shade and shelter to the house.

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