Hazardous heat in Ontario grows with rising severe storm, tornado risk

Yahoo

21-06-2025

Heat and a growing thunderstorm threat this weekend will pose a threat to outdoor plans in southern Ontario.
A large cluster of storms is forecast to sweep across southern Ontario Saturday, but with some uncertainty in timing and intensity. However, there is a widespread chance of severe storms north and east of the Greater Toronto Area (GTA), with torrential rainfall, large hail and potent wind gusts as the main hazards. There is even a tornado risk in northeastern Ontario.
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Be sure to keep an eye on local weather alerts as conditions change.
In addition to the storm threat, high heat and humidity are expected. Together, they are a dangerous combination––even for relatively healthy individuals. Use extreme caution this weekend and next week as temperatures soar.
The ridge of high pressure responsible for the building heat will nudge toward Ontario to start the weekend. This 'ring of fire,' as meteorologists call it, can serve as the focus for development of strong to severe thunderstorms.
These clusters of storms can be quite difficult to forecast—but also quite intense with strong winds, torrential rain, and vivid lightning.
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Renewed rounds of storms are expected to develop Saturday afternoon and continue into the overnight hours.
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The first batch of storms could build through the late afternoon and evening for northeastern, central and eastern Ontario. The second round could arrive late Saturday night and continue into the overnight hours.
There is still lots of uncertainty on how these storms will develop, but all modes of severe weather will be possible—including torrential rains, strong wind gusts, large hail, and even one or two tornadoes in northeastern Ontario (severe-likely region).
Make sure you have a way to receive severe weather warnings the moment they're issued.
We'll see temperatures and humidity increase to dangerous levels as the ridge of high pressure intensifies through the weekend and into next week.
Southern Ontario will endure a multi-day stretch of extreme heat and humidity beginning Sunday, with temperatures climbing into the low- to mid-30s and humidex values rising toward the mid-40s.
Sunday through Tuesday will serve as the focus of the extreme heat and humidity. We're expecting at least three days of temperatures of 33°C or higher across most of the GTA and southwest—with daytime humidex values into the mid-40s.
Overnight lows will remain in the mid 20s, providing little relief for those living without reliable access to air conditioning.
If Toronto airport reaches a temperature of 35°C, likely on Monday, it would fall in the top-10 warmest June days on record.
If we see three or more consecutive days of 33°C or higher at Pearson airport, it will have been 13 years (since 2012) since we experienced a stretch of heat like this in June.
Record-breaking or not, this is an impressive heat wave that needs to be taken seriously.
Drink plenty of water. Avoid caffeine and alcohol, which can be dehydrating.
Avoid direct sunlight, especially during peak hours and when the UV rating is high.
Wear lightweight, loose-fitting clothing.
Use air conditioning when possible. If you do not have access to air conditioning, consider visiting a cooling centre, a shopping centre, or a public library.
Check on elderly relatives and other vulnerable neighbors.
Avoid strenuous activities during the hottest parts of the day.
If you experience symptoms of heat-related illnesses like dizziness, nausea, or confusion, seek medical attention.
Stay with The Weather Network for all the latest on conditions across Ontario.
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