4:46 a.m. EDT Tuesday 30 June 2026
Impact Level: High
Forecast Confidence: Very High
A long duration heat event begins today.
What:
Maximum temperatures of 31 to 34 degrees Celsius, and potentially up to 37 degrees Celsius for some areas.
Minimum temperatures of 21 to 25 degrees Celsius.
When:
Today through Friday, and possibly into the weekend.
Additional Information:
The hottest days are expected to be Wednesday and Thursday, with maximum temperatures of 34 to 37 degrees Celsius expected. Minimum temperatures of 21 to 25 degrees Celsius will provide little relief from the heat.
Hot and humid air can also bring deteriorating air quality and can result in the Air Quality Health Index approaching the high-risk category.
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.
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.
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: https://www.canada.ca/en/health-canada/services/climate-change-health/extreme-heat/how-protect-yourself.html https://www.canada.ca/en/health-canada/services/climate-change-health/extreme-heat/who-is-at-risk.html
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.
In effect for:- St. Catharines - Grimsby - Northern Niagara Region
