Heat wave could last until Thursday
TORONTO, July 12, 2025 – Southern Ontario is in the throes of its third severe heat warning of the summer, with temperatures expected to hit as high as 32 celsius upwards of 40 celsius with the Humidex, according to Environment and Climate Change Canada. So, it is going to be a little hotter than usual at this year’s Toronto Outdoor Art Fair and anywhere else in TO this weekend. The sweltering days are expected to last until Thursday, with the hottest day being today, Saturday.
Over the next few days all of southern Ontario and Quebec for that matter, will experience hot and humid conditions. The temperatures and humidex will meet or be extremely close to heat warning criteria, with the hottest day being today. A shift in the weather pattern on Thursday will likely end this multi-day period of heat and humidity.
Heat Warning issues by Environment and Climate Change Canada for the following areas of Southern Ontario:
Simcoe – Delhi – Norfolk; Dunnville – Caledonia – Haldimand; Watford – Pinery Park – Eastern Lambton County; Sarnia – Petrolia – Western Lambton County; Chatham-Kent – Rondeau Park; Windsor – Leamington – Essex County; London – Parkhill – Eastern Middlesex County; Strathroy – Komoka – Western Middlesex County; St. Thomas – Aylmer – Eastern Elgin County; Rodney – Shedden – Western Elgin County; Woodstock – Tillsonburg – Oxford County; Brantford – County of Brant; City of Toronto; Uxbridge – Beaverton – Northern Durham Region; Newmarket – Georgina – Northern York Region; Pickering – Oshawa – Southern Durham Region; Vaughan – Richmond Hill – Markham; Belleville – Quinte West – Eastern Northumberland County; Cobourg – Colborne – Western Northumberland County; Tamworth – Sydenham – South Frontenac; Stirling – Tweed – Madoc; Kingston – Odessa – Frontenac Islands; Napanee – Consecon; Merrickville-Wolford – Kemptville; Westport – Charleston Lake; Brockville – Prescott; Gananoque – Mallorytown; Maxville – Alexandria; Cornwall – Lancaster; Winchester – Newington; Morrisburg – Long Sault; Lindsay – Southern Kawartha Lakes; Peterborough City – Lakefield – Southern Peterborough County; Prescott and Russell; Smiths Falls – Perth – Eastern Lanark County; Plevna – Sharbot Lake – Western Lanark County; Ottawa North – Kanata – Orléans; Ottawa South – Richmond – Metcalfe; City of Hamilton; Guelph – Erin – Southern Wellington County; Kitchener – Cambridge – Region of Waterloo; Caledon; Mississauga – Brampton; Halton Hills – Milton; Burlington – Oakville; St. Catharines – Grimsby – Northern Niagara Region; Niagara Falls – Welland – Southern Niagara Region
Just the Details
Heat Warning in effect for:
- Ottawa North – Kanata – Orléans
A prolonged period of near heat warning levels continues.
What: Daytime highs of 29 to 32 degrees Celsius and a humidex of 35 to 40.
Overnight lows of 19 to 23 degrees Celsius, providing little relief from the heat.
When: Continuing possibly till Thursday.
How to protect yourself and loved ones from this heat
Take action to protect yourself and others – extreme heat can affect everyone’s health. Determine if you or others around you are at greater risk of heat illness.
Check on older adults, those living alone and other at-risk people in-person or on the phone multiple times a day.
Watch for the early signs of heat exhaustion in yourself and others. Signs may include headache, nausea, dizziness, thirst, dark urine and intense fatigue.
Stop your activity and drink water.
Signs of heat stroke
Heat stroke is a medical emergency! Call 9-1-1 or your emergency health provider if you, or someone around you, is showing signs of heat stroke which can include red and hot skin, dizziness, nausea, confusion and change in consciousness. While you wait for medical attention, try to cool the person by moving them to a cool place, removing extra clothing, applying cold water or ice packs around the body.
What to do to avoid overheating
Drink water often and before you feel thirsty to replace fluids.
Close blinds, or shades and open windows if outside is cooler than inside.
Turn on air conditioning, use a fan, or move to a cooler area of your living space.
If your living space is hot, move to a cool public space such as a cooling centre, community centre, library or shaded park.
Follow the advice of your region’s public health authority.
Plan and schedule outdoor activities during the coolest parts of the day.
Limit direct exposure to the sun and heat.
Wear lightweight, light-coloured, loose-fitting clothing and a wide-brimmed hat.
Never leave people, especially children, or pets inside a parked vehicle. Check the vehicle before locking to make sure no one is left behind.
For more information about heat related treatment and prevention
For more information: How to protect yourself from the health effects of extreme heat Health risks and who is at risk of extreme heat events
Please continue to monitor alerts and forecasts issued by Environment Canada. To report severe weather, send an email to ONstorm@ec.gc.ca or post reports on X using #ONStorm.
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