Hottest temperatures of the year set to hit southern Ontario this week
The hottest temperatures of the year are forecast in the Greater Toronto Area (GTA) this week, with daytime highs soaring into the 30s and humidex values returning to the 40s
Ontario is gearing up for its second significant heat event of the summer, with temperatures and humidex values set to rise substantially this week.
Daytime highs are expected to soar well into the 30s, with humidex levels potentially surpassing the 40s during the peak of this heat event.
FORECAST: Severe storms and isolated tornado risk for parts of Ontario, Quebec
Even a relatively healthy individual can succumb to heat-related illnesses without proper precautions.
What could compound the heat issues will be the wildfire smoke that has reached parts of the province from Quebec, lowering air quality into this week.
Second heat event of the summer arrives
On Sunday, temperatures felt like the low 40s across northwestern Ontario as the heat and humidity continued to ramp up. Over twenty weather stations across the province recorded daytime temperatures above the 30-degree mark, and even hotter weather is still on the way.
In fact, one northwestern Ontario town now holds Canada's record for highest daytime temperature so far in 2026. Sioux Lookout, located north of Dryden, reached 38°C on Sunday!
The heat trophy may go to Sioux Lookout, but the temperatures felt in other communities throughout the region on Sunday were also noteworthy:
Atikokan: 37.0°C
Ear Falls: 36.4°C
Fort Frances: 36.1°C
Pickle Lake: 35.3°C
Kenora: 35°C
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Temperatures across northern Ontario will climb significantly on Monday, with daytime highs in the mid to high 30s. Humidex values are expected to make it feel like the low 40s in many regions. In contrast, areas near Lake Superior, under the influence of a cool lake breeze, will feel much cooler—Marathon is forecast to reach just 17°C.
Thunder Bay is set to hit a sweltering 38°C by Monday afternoon, just shy of its all-time record high of 40.3°C, recorded on August 7, 1983.
In southern Ontario, daytime highs are forecast to range from the high 20s to low 30s, with humidex values reaching the high 30s.
Toronto's hottest day of the year on Tuesday?
The heat will intensify further on Tuesday for southern and eastern Ontario, making it likely the hottest day of the week. Temperatures are expected to soar into the high 30s, with humidex readings nearing the high 40s. Toronto could see a high of 37°C, potentially marking the hottest temperature of the year, surpassing the 36°C recorded on July 1.
Muggy conditions will create uncomfortable outdoor environments, and those at risk for heat-related illnesses should limit time outside and stay hydrated.
Tuesday's forecast humidex
Toronto: 46
London: 46
Windsor: 46
Kingston: 41
Ottawa: 45
Parry Sound: 38
A cold front is forecast to move into southern Ontario late Tuesday, bringing Wednesday's temperatures back down toward the 30-degree mark with humidex values staying in the low-to-mid 30s.
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Heat safety is vital
Extreme heat claims more lives around the world than any other type of severe weather.
Everyone is susceptible to heat-related illnesses without taking proper precautions, such as frequent breaks, adequate hydration, and air conditioning.
The compounding stress of hot days followed by muggy nights can be especially hard on vulnerable populations like the elderly, those with chronic health conditions, and folks who live without access to air conditioning. Keep in mind that certain medications can lower your body’s heat tolerance.