Heat dome to peak Canada Day with 40 C humidex

A significant heat event is expected to build across southern Ontario next week, including Toronto, with humidex values potentially reaching the low 40s, according to The Weather Network.

The heat is expected to begin Sunday, June 28 and persist throughout the week. Daytime highs will generally range from the low to mid-30s Celsius on most days. However, on Canada Day, July 1, the humidex could make it feel like temperatures are in the low 40s, potentially marking the peak of the heat event.

Environment Canada's Toronto forecast shows the city warming sharply into next week, with highs of 32°C on Tuesday, June 30 and 33°C on Canada Day, along with a chance of showers or thunderstorms. Toronto's seasonal normal for this time of year is 26°C, meaning next week's daytime highs could sit several degrees above average.

With many people planning to spend time outdoors for Canada Day celebrations—at the beach, hosting barbecues, or attending community events—Torontonians are being urged to take precautions against heat-related illness by staying hydrated, limiting strenuous outdoor activity during peak afternoon hours, and seeking shade or air-conditioned spaces when possible. The Weather Network notes that heat domes are stationary areas of high pressure that trap hot air beneath them, leading to prolonged periods of above-seasonal temperatures. Forecasters are also monitoring the potential for thunderstorms throughout the week as heat and humidity continue to build.