Extreme Heat Alert Issued for Southern Ontario

Toronto is about to get its first heat wave of 2025 and it is expected to reach dangerous levels

TORONTO, June 21, 2025 – Things are about to heat up to dangerous levels in southern Ontario on Sunday, and the heat wave is expected to continue into Tuesday. Environment and Climate Change Canada has issued a Severe Weather Warning for dangerous heat and humidity beginning Sunday afternoon. Temperatures are expected to reach as high as 35 celsius Sunday and 37 on Monday carrying through to Tuesday morning.

The first significant heat event of the season with dangerously hot and humid conditions will begin Sunday afternoon and is expected to continue into the week.

What

Daytime highs of 31 to 36 degrees Celsius. Humidex values of 40 to 45. Overnight lows of 21 to 25 degrees Celsius, providing little relief from the heat.

When

Sunday afternoon to Tuesday night.

Additional information: The extreme heat and humidity may continue into Wednesday. A cold front is expected to push through the region late Tuesday but there is some uncertainty with how far south this front will get. Should it remain farther north, the heat event may continue for Wednesday primarily for southwestern Ontario and the GTA.

Where

Simcoe – Delhi – Norfolk; Dunnville – Caledonia – Haldimand; 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; Picton – Sandbanks Park; Merrickville-Wolford – Kemptville; Westport – Charleston Lake; Brockville – Prescott; Gananoque – Mallorytown; Maxville – Alexandria; Cornwall – Lancaster; Winchester – Newington; Morrisburg – Long Sault; Midland – Coldwater – Orr Lake; Orillia – Lagoon City – Washago; Barrie – Collingwood – Hillsdale; South River – Burk’s Falls; Bayfield Inlet – Dunchurch; Deep River – Whitney – Eastern Algonquin Park; Western Algonquin Park – Lake of Two Rivers; Huntsville – Baysville; Town of Parry Sound – Rosseau – Killbear Park; Port Carling – Port Severn; Bracebridge – Gravenhurst; Oxtongue Lake – Fort Irwin – Northern Haliburton County; Haliburton – Minden – Southern Haliburton County; Bancroft – Hastings Highlands – Denbigh; Kaladar – Bannockburn – Bon Echo Park; Fenelon Falls – Balsam Lake Park – Northern Kawartha Lakes; Apsley – Woodview – Northern Peterborough County; Lindsay – Southern Kawartha Lakes; Peterborough City – Lakefield – Southern Peterborough County; Prescott and Russell; Petawawa – Pembroke – Cobden; Barry’s Bay – Killaloe; Renfrew – Arnprior – Calabogie; Smiths Falls – Perth – Eastern Lanark County; Plevna – Sharbot Lake – Western Lanark County; Ottawa North – Kanata – Orléans; Ottawa South – Richmond – Metcalfe; City of Hamilton; Bruce Peninsula – Sauble Beach – Tobermory; Owen Sound – Blue Mountains – Northern Grey County; Saugeen Shores – Kincardine – Southern Bruce County; Hanover – Dundalk – Southern Grey County; Wingham – Blyth – Northern Huron County; Listowel – Milverton – Northern Perth County; Goderich – Bluewater – Southern Huron County; Stratford – Mitchell – Southern Perth County; Mount Forest – Arthur – Northern Wellington County; Guelph – Erin – Southern Wellington County; Kitchener – Cambridge – Region of Waterloo; Innisfil – New Tecumseth – Angus; Shelburne – Mansfield – Northern Dufferin County; Orangeville – Grand Valley – Southern Dufferin County; Caledon; Mississauga – Brampton; Halton Hills – Milton; Burlington – Oakville; St. Catharines – Grimsby – Northern Niagara Region; Niagara Falls – Welland – Southern Niagara Region

Advice for residents

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.

Know the early signs of heat exhaustion

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. Heat stroke is a medical emergency!

What to do in case of heat exhaustion

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.

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.

How to 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: 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.

posted by Terry Lankstead with info from Environment and Climate Change Canada

Other articles from totimes.ca – otttimes.ca – mtltimes.ca