Residents of Waterloo and surrounding areas are facing a multi-day heat wave this week, with humidex values making it feel as hot as 36 by Monday afternoon. Environment Canada has issued a heat warning for Waterloo Region, Guelph and Wellington County that started Monday July 13 and could last into Wednesday or Thursday evening.
On Monday at 3 p.m., the temperature at the Region of Waterloo International Airport already hit 30.5°C with a humidex of 36. Forecasters say Tuesday will be the hottest day, with the mercury climbing to 35°C and a humidex of 43. Some parts of southwestern Ontario could see humidex readings as high as 45, according to Environment Canada.
Overnight lows are expected to stay between 20°C and 24°C, offering little relief. The UV index on Tuesday is forecast to hit 9, which is considered very high, so sunscreen and shade are essential for anyone heading outside. The heat may also worsen air quality, with the Air Quality Health Index possibly reaching the high-risk category.
Local paramedics are preparing for another busy stretch. During the Canada Day heat wave at the end of June, emergency calls jumped by 14 to 14.5 per cent compared to the same period in 2025. To help people cope, cooling spaces are open across the region at city halls, township offices, community centres, library branches and shopping malls during regular business hours.
Some relief is on the way. Showers are expected to return Wednesday with a 30 per cent chance, and showers could continue through the weekend.
