Prolonged Heat Wave and Severe Storms Impact Ontario, Quebec, and the Maritimes

A prolonged and intense heat wave has swept across much of eastern Canada, impacting Ontario, Quebec, and the Maritime provinces, with Environment Canada issuing heat warnings for large swathes of the country. The event, characterized by sustained high temperatures and elevated humidity, has been driven by a 'heat dome'—a high-pressure system trapping hot, humid air over the region and preventing cooling ventilation.

In Toronto, Environment Canada recorded a temperature of 35.9 C at Pearson Airport by 4 p.m. on Canada Day, with the humidex making it feel closer to 48 C. This marked the warmest Canada Day on record at Pearson since its opening in 1938, though it fell just short of the city’s all-time July 1 record of 36.7 C, set in 1911 and 1931. With overnight lows offering little relief—temperatures in Toronto were expected to dip only to 24 C—health officials and climatologists expressed concern about the cumulative health impacts, especially as the heat event persisted for multiple days.

Environment Canada issued orange-level heat warnings for much of southern Ontario, from Windsor through Ottawa and Thunder Bay, and for large areas of Quebec, including Montreal and Quebec City. Forecasts predicted daytime highs between 31 C and 37 C, with humidex values in some areas reaching 44–45 C. In Quebec, Montreal saw temperatures around 32 C, prompting public health officials to urge residents, especially those moving on the province’s traditional July 1 'moving day,' to hydrate and take frequent breaks. Heat warnings extended eastward to New Brunswick, Nova Scotia, and Prince Edward Island, where temperatures were forecast to reach 29 C but feel closer to 41 C with humidity. Overnight lows in the Maritimes hovered around 18–20 C, with warnings in place for Thursday and Friday.

The duration of the heat wave, rather than the absolute temperature, has been flagged as the main risk by meteorologists. Peter Kimbell, a warning preparedness meteorologist with Environment and Climate Change Canada, noted that the orange alert level—introduced in late 2025—was triggered due to the expectation of four consecutive days of high heat. He emphasized that this level of sustained heat can be dangerous, particularly for vulnerable groups. Climatologist David Phillips highlighted that the first heat wave of the summer is often the most dangerous, as people are not yet acclimatized, and that high nighttime temperatures increase risk, as the body cannot recover.

Across affected regions, public health authorities have urged residents to drink water, avoid strenuous activity during peak heat, stay in shaded or air-conditioned spaces, and check on those at greater risk—such as the elderly, infants, people with chronic illnesses, and those experiencing homelessness. Michelle Murti, Toronto’s medical officer of health, and Dr. Nicola Mercer, medical officer of health for Wellington-Dufferin-Guelph, reiterated that heat-related illnesses can affect anyone and are preventable with appropriate precautions. Signs of heat exhaustion include headache, nausea, dizziness, thirst, dark urine, and extreme tiredness, while heat stroke—marked by confusion, hot red skin, and changes in consciousness—is a medical emergency.

The City of Toronto expanded cooling measures, opening 24-hour cooling centres and activating its heat relief network, which includes libraries, community centres, and pools. Outreach organizations such as Fred Victor deployed teams to distribute water and sunscreen to unhoused residents and direct people to cooling spaces. Fred Victor CEO Keith Hambly highlighted additional vulnerabilities among those with chronic health conditions or who take medications requiring temperature control, and noted increased risks for people using drugs outdoors following the closure of supervised consumption sites.

The heat wave has coincided with severe thunderstorms across Ontario and Quebec, leading to widespread power outages. Hydro One in Ontario reported up to 168,000 customers without power at one point, with outages affecting regions such as Barrie, Alliston, Orillia, Newmarket, and Huntsville. Hydro-Quebec reported more than 10,000 homes and businesses off the grid. In some areas, including Simcoe County, restoration efforts continued into Thursday, with utilities urging residents to avoid downed lines and promising 24/7 work until service was restored.

Severe storms brought additional hazards, including wind gusts up to 100 km/h, hail up to 4 cm in diameter, and torrential rainfall. Ottawa Airport recorded approximately 110 mm of rain. In central Ontario, storms caused significant tree damage and further outages, but no injuries were reported in Barrie. The National Capital Region cancelled several Canada Day events, including fireworks, due to safety concerns. Environment Canada warned of the potential for flash flooding, property damage, and injury from falling branches, strong winds, and hail. Residents were urged to monitor alerts and secure loose outdoor items.

In the agricultural sector, southwestern Ontario farmers expressed mixed responses to the extreme weather. Following weeks of storms—including tornadoes and hail that damaged crops—some welcomed the heat as beneficial for corn and pumpkin growth, though others noted that the combination of wet and dry spells had complicated planting and affected crop maturation and yields. Farmers observed that the timing and variability of conditions have led to smaller vegetables and potentially delayed or shortened produce availability for consumers.

In response to the heat, some public events were cancelled, including Toronto’s World Cup broadcasts at Nathan Phillips Square and community events in London repurposed as cooling centres. Beachgoers in Durham Region were advised to avoid swimming at four public beaches due to unsafe E. coli levels, possibly exacerbated by recent storms and runoff. Public health guidance suggested avoiding swimming after heavy rains or when water is cloudy.

The extreme heat also prompted new discussions about tenant rights and building adaptation. As of July 1, Ontario tenants have the explicit right to install air conditioning units if not supplied by landlords, subject to conditions intended to prevent damage and allow landlord inspection. The move is part of a broader adaptation to more frequent and severe heat events attributed to climate change.

Looking ahead, meteorologists indicated that while a slight moderation in temperatures was expected in some areas the following week, forecasts suggested further heat waves could occur later in the summer. The late July to early August period is historically the hottest for southern Ontario, and experts cautioned that this current heat wave may not be the last of the season.

The evolving climate patterns and the impacts of prolonged heat underscore the need for continued public health vigilance, infrastructure adaptation, and community support, particularly for vulnerable populations. Authorities continue to stress the importance of collective action, both in immediate response to extreme weather and in long-term planning for a warmer future.