Widespread warnings as Ontario and Quebec enter into second day of heat wave

Temperatures will jump into the 30s for most of Ontario and Quebec this week as potentially record-setting, and dangerous, heat moves into the provinces

While some individuals are more prone to health risks during times of hot weather, extreme heat can affect everyone.

Such is the case in Ontario and Quebec this week as the mercury soars to the 30s, with humidex levels stretching into the 40s for many locales. Hot and humid air can also bring deteriorating air quality, and can result in the air quality health index (AQHI) getting near the high-risk category.

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The heat will arrive ahead of the summer solstice, and well before Saint-Jean-Baptiste Day in Quebec.

Watch out for heat-related impacts, such as heat exhaustion and/or heat stroke. Remember to drink plenty of water. Avoid strenuous work outdoors.

The heat and humidity will also fuel daily thunderstorm risks, so people will need to be weather-aware.

Major heat builds over the region

This week’s heat wave could break records across Ontario and Quebec as a strong ridge of high pressure builds over the eastern U.S. and the Great Lakes.

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Air sinks beneath a strong ridge, warming up as it descends toward the surface. Hot, muggy winds blowing straight from the Gulf of Mexico will add tropical humidity to the mix.

Ontario and Quebec June humidex records_June 17

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Between the ridge and the humidity combined, we're in for a days-long stretch of hot daytime highs and little to no relief from the stuffy air at night.

The heat arrives in earnest Tuesday through Thursday as daytime high temperatures climb into the lower to middle 30s for just about everyone throughout southern Ontario and southern Quebec. Widespread heat warnings are in effect.

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Humidex values could climb as high as the mid-40s throughout the Greater Toronto and Hamilton Area, in and around Ottawa, and across Montreal.

Ontario and Quebec Thursday temperatures and feels-like values_June 17

Humidex records will be challenged all across Ontario, and will be similar in magnitude to the June-July 2018 heat wave event. As we continue to move in the direction of a warming world, extreme heat events like these are expected to increase in frequency.

Air quality in the region will likely suffer due to this stagnant, humid air mass.

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Extreme heat has a compounding effect on your body. This level of heat could cause heat-related illnesses in even healthy individuals.


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The only potential relief from this predicted heat will come from scattered thunderstorms that may erupt in the hot and humid air parked over Ontario and Quebec.

Any storms or clouds will help to cap daytime temperatures, even if only for a little while.

Tuesday could bring a few scattered thunderstorms south and east of Georgian Bay, and may offer some brief relief from the heat.

Tuesday southern Ontario and Quebec storm risk map_June 17

If storms do materialize Tuesday, some could reach severe warning criteria in locales stretching from southern Lake Huron to parts of eastern Ontario. The main hazards will be strong wind gusts, large hail and heavy rain.

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Increased potential for heat-related illnesses

Extreme heat is a leading weather-related cause of death around the world, claiming more lives every year than tornadoes and hurricanes combined. Hot temperatures are truly a silent killer.

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Explainer: Heat Stroke, heat exhaustion symptoms, health

Folks who are highly susceptible to the heat include those in homes without air conditioning, elderly people, unhoused people, outdoor workers, those living with chronic health conditions, and folks taking certain medications.

Check on vulnerable friends, family, and neighbours over the coming week. Stay alert for the signs of heat-related illnesses.

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Heat exhaustion occurs when a person’s body temperature climbs too high and they struggle to cool off. Symptoms of heat exhaustion include dizziness, excessive sweating, and weakness. Developing heat exhaustion is a serious sign that your body is in distress and you need to find a way to cool off immediately.

Heat stroke is a life-threatening medical emergency that occurs when a person’s body temperature is so high that their vital systems begin to shut down.

During heat stroke, sweat production stops and body temperatures soar very quickly. A victim suffering from heat stroke may exhibit confusion and loss of consciousness. Heat stroke can be fatal if not treated immediately.

Why heat waves aren’t ‘just summer weather’

The risk for heat-related illnesses will sharply increase during this upcoming heat wave as a result of the expected duration of hot temperatures and high humidity.

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Humid air retains heat better than dry air, so nighttime temperatures won’t cool off enough to provide meaningful relief for folks without reliable access to air conditioning.

extreme heat safety tips

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Hot days running into stuffy nights will compound the effects of high heat on the human body, resulting in an increased potential for heat exhaustion and heat stroke.

Simply circulating air with fans won’t be enough to provide necessary relief from this level and duration of high heat. Air conditioning is a vital survival tool during a days-long heat wave.

Take advantage of community cooling centres if they’re available. Stay well-hydrated throughout the week, and avoid strenuous work outdoors during the heat of the day.

Stay with The Weather Network for all the latest on this impending heat wave.

Thumbnail image courtesy: Getty Images

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