Published on Jun. 9, 2026, 11:35 AM
Ontario will see high heat and humidity this week, with humidex values nearing the 40s and increasing thunderstorm risks from Tuesday through Thursday, bringing potential for torrential downpours, localized hail, and strong winds
Ontario will experience a surge in heat and humidity this week as high atmospheric moisture and low pressure systems approach the Great Lakes. Temperatures will feel like the 30s, with humidex values nearing the 40s. The warmest days are forecast for Wednesday and Thursday.
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The muggy air will help to fuel a thunderstorm risk with the threat for torrential downpours at times.
Thunderstorm risk returns to southern Ontario Tuesday
Thunderstorm activity begins Tuesday afternoon in southwestern Ontario, the Lake Huron shores, and cottage country.
The Greater Toronto Area (GTA) may see evening and overnight storms.
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These storms will be slow-moving, with the potential for heavy to torrential downpours.
Heavy rain and hail risk in eastern Ontario Wednesday
On Wednesday, isolated thunderstorms may develop in eastern Ontario, including Petawawa, Ottawa, and Cornwall, bringing a risk of intense rainfall, localized hail near 2 cm, and slow storm movement.