Environment Canada has issued a heat warning for the city of Toronto, the GTA and much of southern Ontario, with humidex values expected to reach the equivalent of 40 C on Sunday.

A warm front is expected to bring a flow of hot and humid air over southern Ontario. Environment Canada says current information suggests daytime highs near 31 C and low temperatures near 21 C for Sunday and Monday.

A special air quality statement has also been issued for the city on Sunday. The weather agency says the statement is in place due to the possibility of deteriorating air quality and high levels of air pollution.

“Hot and sunny conditions are expected to cause increasing ground-level ozone concentrations in southwestern Ontario and the Golden Horseshoe area,” says Environment Canada in a statement.

The weather agency is warning that individuals may experience symptoms such as increased coughing, throat irritation, headaches, or shortness of breath. People who suffer lung diseases, such as asthma and COPD, are at high risk due to air pollution.

The humidex, a Canadian creation first used in 1965, combines temperature and humidity levels into one value intended to show the temperature the average adult will perceive it to be, even if the actual temperature value is lower. It’s intended to measure comfort: a 40 on the humidex signals that you aren’t in danger from heat stroke yet, but there could be great discomfort from the heat, especially if you are engaging in a lot of physical activity outside.

The risk is elevated for young children, the elderly, those battling illness, or people working or exercising outdoors, Environment Canada says. The agency reminds people never to leave children or pets in parked vehicles.

As well as a high humidex, Monday may also have some rain, with scattered showers predicted for the afternoon and a risk of a thunderstorm.

The skies may become cloudier as the day goes on, with wind gusting west from 30 to 50 km/h in the morning. The temperature is predicted to be only slightly cooler than Sunday, with a high of 31 C.

A cold front crossing southern Ontario is expected to cut through the heat on Monday night, and by Tuesday, the city should be waking up to a more manageable heat, with an expected high of 25 C. Mid to high 20s are predicted for the remainder of the week.

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With files from Bryann Aguilar

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