Extreme Heat Grips Ontario as Temperatures Soar Above 35 C in Some Regions

A widespread heat event continued across much of Ontario on Monday, bringing dangerously high temperatures and humid conditions that are expected to persist into Tuesday in many areas.

Large portions of northern, northwestern and southern Ontario face a significant risk of heat-related illnesses, including heat exhaustion and heat stroke, as daytime temperatures climb well above seasonal averages.

The most intense heat is expected across parts of northwestern Ontario and areas north of Lake Superior, where daytime highs are forecast to reach between 35 C and 40 C. Overnight temperatures are expected to remain elevated between 20 C and 23 C, providing little relief from the heat. Humidex values could climb into the high 30s and mid-40s.

Temperatures of this magnitude have not been experienced in some of these regions for many years.

Across most of northern Ontario and southern portions of the far north, temperatures are expected to range from 33 C to 36 C through Tuesday. Overnight lows are forecast to remain between 20 C and 23 C, while humidex values are expected to reach the high 30s to mid-40s.

Southern Ontario, along with southern parts of northeastern Ontario and portions of the far north, is also entering a prolonged period of hot weather. Daytime temperatures are expected to reach between 30 C and 33 C, with overnight lows near 20 C. Humidex values are forecast to rise into the mid to high 30s.

Meanwhile, communities along the shores of Lake Superior and near Hudson Bay are expected to experience somewhat lower temperatures, though conditions will still be unseasonably warm. Highs between 27 C and 30 C are possible, with overnight lows around 17 C and humidex values in the low to mid-30s.

Health officials are encouraging residents to take precautions during the heat event by staying hydrated, limiting strenuous outdoor activities, seeking air-conditioned spaces when possible, and checking on vulnerable individuals, including seniors, young children and those with underlying health conditions.

The heat is expected to continue through at least Tuesday in many regions.

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Forecast confidence:

High

Impact scale:

Moderate

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Extreme heat can become dangerous quickly. Here are some important safety tips:

Stay Hydrated

• Drink water regularly, even if you don’t feel thirsty

• Avoid too much caffeine or sugary drinks

• During heavy activity outdoors, take frequent water breaks

Stay Cool Indoors

• Use air conditioning if possible

• Close blinds or curtains during the hottest part of the day

• Use fans, but remember that fans alone may not prevent heat illness in extreme temperatures

Avoid Peak Heat

The hottest part of the day is usually between 11 a.m. and 4 p.m.

• Limit strenuous outdoor activities during this time

• Schedule exercise or yard work early morning or evening

Dress for the Heat

• Wear lightweight, loose-fitting, light-coloured clothing

• Use a wide-brimmed hat and sunscreen outdoors

  
  

Never Leave People or Pets in Vehicles

Temperatures inside a parked car can rise dangerously fast — even with windows cracked open.

Watch for Heat Illness

Signs of heat exhaustion:

• Heavy sweating

• Dizziness

• Weakness

• Nausea

• Headache

Move to a cool place and drink water.

Signs of heat stroke (medical emergency):

• Confusion

• Fainting

• Very high body temperature

• Hot, dry skin or stopped sweating

Call emergency services immediately if someone shows signs of heat stroke.

Check on Vulnerable People

Older adults, infants, young children, outdoor workers, and people with health conditions are at higher risk.

Protect Pets

• Ensure pets always have fresh water and shade

• Avoid walking dogs on hot pavement

• Watch for overheating signs like excessive panting or lethargy