Southern Ontario has been experiencing a prolonged heat wave throughout July 2025, with Environment Canada issuing multiple heat warnings for the region. The heat wave has brought hot, muggy conditions, with temperatures in Toronto reaching a heat index of around 40 degrees Celsius. This period of elevated temperatures has been accompanied by deteriorating air quality, prompting special air quality statements and health advisories in Toronto and other parts of southern Ontario. The poor air quality has been exacerbated by lingering wildfire smoke, contributing to some of the worst air quality levels globally in Toronto. Additionally, a multi-day threat of severe thunderstorms, including heavy downpours, large hail, and strong winds, has been forecasted for southern Ontario and Quebec, with a low-pressure system expected to bring these conditions from Friday through Sunday. The storm risk has shifted south and east, affecting eastern Ontario and southern Quebec. Nearby regions such as the Chicago area and parts of New York have also issued air quality alerts amid similar heat and smoke conditions. Environment Canada forecasts that an incoming cooler air mass should bring an end to the heat wave in Toronto by Thursday night.