Prepare for powerful thunderstorms across Ontario and Quebec
Sunday, July 6, 2025 – Ottawa, Ontario – Widespread thunderstorms, some severe, are set to impact Southern Ontario and Southern Quebec this Sunday, driven by a potent mix of heat, humidity, and an incoming cold front. Conditions will feel tropical, with humidex values climbing dramatically across the region, making for an unstable atmosphere primed for storm development.
High heat and unstable air over Southern Ontario
By early Sunday afternoon, areas stretching from Windsor through the Greater Toronto Area, the Ottawa Valley, and into Quebec City will experience elevated chances of thunderstorm activity. A low-pressure system, fed by high humidity, will sweep across Ontario, increasing the likelihood of localized flooding, strong wind gusts, and hail.
Severe storm risk in Southwestern Ontario and Eastern Quebec
The most intense weather is expected to develop in two main regions:
Southwestern Ontario, including communities near Lake Huron, Georgian Bay, and extending toward Cottage Country, will likely see storms forming by early evening. The main hazards here include short bursts of torrential rain, potentially causing flooding, along with hail and gusty winds.
Simultaneously, a warm front lifting through Eastern Ontario and into Southern Quebec—including Ottawa, Montreal, and nearby areas—will provide the trigger for stronger storm cells. These could carry wind gusts reaching 110 km/h (68 mph) and nickel-sized hail, with rotation not completely ruled out. Due to the high moisture levels, even brief storms may dump significant rainfall, leading to localized flood concerns.
Be weather aware throughout Sunday
As you move through your Sunday plans, keep close tabs on weather alerts. The risk of severe thunderstorms stretches well beyond urban centres into rural and cottage regions. Conditions may change rapidly, especially in Eastern Ontario and Southern Quebec, where instability will peak in the late afternoon into evening hours.
Stay tuned for updated watches and warnings, and monitor radar frequently if you’re travelling or spending time outdoors across Ontario and Quebec.
