A warmer-than-average summer is coming to Ontario
As May closes and June prepares to roll in, the long-awaited 2025 summer forecast for Ontario has arrived, and it’s shaping up to be warmer, more humid, and stormier than usual. According to The Weather Network, much of Canada is bracing for a hot season, and Ontario is fully in line with this trend.
Southern and eastern Ontario: early heat and high humidity
Cities like Toronto, Ottawa and London will see an early onset of summer heat, with June expected to jump-start warm conditions, possibly bringing the first heat wave before Canada Day.
Despite stretches of hot and humid days, cooler air masses may occasionally sweep through, delivering brief periods of relief. However, daytime highs are projected to remain near to slightly above seasonal norms, and night temperatures will likely stay elevated, intensified by persistent humidity.
Frequent thunderstorms and moist conditions
The muggy air expected to blanket much of the province will also act as a catalyst for thunderstorms. With precipitation totals forecasted to be near or slightly above average, expect frequent showers and the occasional storm system. Still, meteorologists anticipate occasional stretches of dry weather, especially toward the mid-summer period, though no prolonged drought is in sight for southern and eastern Ontario.
Northern Ontario: mixed signals and wildfire risks
The picture becomes more complex in northern Ontario, particularly when comparing the western and eastern sides of Lake Superior.
Western areas, including Thunder Bay, are likely to experience a hot and dry summer, which elevates the wildfire threat, especially north and west of Lake Superior. If realized, this could again bring poor air quality and heavy smoke across parts of Ontario, as seen during the wildfire season of 2023.
In contrast, eastern parts of northern Ontario, such as Sudbury, should expect warmer-than-usual conditions, accompanied by elevated humidity levels. This combination will lead to frequent showers, thunderstorms, and oppressively warm nights, though daytime temperatures may remain more moderate compared to the west.
Atlantic hurricane season and its impact on Ontario
Although Atlantic hurricane activity is expected to be near or slightly above average, with fewer tropical storms than recent years, the jet stream configuration might still steer a tropical system toward the northeastern United States. If that occurs, eastern Ontario may experience secondary effects, including heavy rains and gusty winds.
As the calendar flips to June, residents across Ontario should prepare for a dynamic summer, characterized by heat, humidity, intermittent storms, and regional wildfire concerns.
