Heat warning continues for Montreal area as humidex nears 42

A woman reads in the St. Lawrence River in the Verdun borough of Montreal on Wednesday, July 16, 2025. THE CANADIAN PRESS/Christinne Muschi

Environment Canada has extended a heat warning for the Montreal area, with temperatures expected to feel like the low 40s with the humidex through Friday.

The warning, issued early Thursday, covers Metro Montreal, Laval and the Vaudreuil area.

The sweltering conditions come following a hot, and in some places volatile, Canada Day, when severe thunderstorms swept across southern Quebec, prompting a brief tornado alert in the Lanaudière and Laurentians regions and forcing the cancellation of evening festivities in Ottawa.

Ottawa hit by major rainfall

As of Wednesday, Environment Canada said roughly 110 millimetres of rain had fallen at the Ottawa Airport.

At one point, Hydro One in Ontario was reporting 168,000 customers in the dark.

Hydro-Quebec also reported that a little more than 10,000 homes and businesses were off the grid.

As of Wednesday morning, that number was down to about 4,20 address, with 2,300 of those in the Outaouais region.

READ MORE: Heat wave gripping much of Ontario, Quebec tracks east to Maritime provinces

Sweltering heat

Daytime highs in Montreal are forecast to reach 31 to 33 C on Thursday and Friday, with humidex values between 40 and 42. Overnight lows between 20 and 24 C will offer little relief.

Cooler, less humid conditions are expected to move in Saturday.

• Hourly and 7-day forecast on our CTVNewsMontreal.ca weather hub

Watch out for at-risk individuals

The weather agency is urging people to check on older adults, those living alone and other at-risk individuals multiple times a day, either in person or by phone.

Early signs of heat exhaustion include headache, nausea, dizziness, thirst, dark urine and intense fatigue. Anyone experiencing these symptoms should stop their activity and drink water.

Heat stroke — marked by red and hot skin, dizziness, nausea, confusion or a change in consciousness — is a medical emergency. Environment Canada says to call 911 immediately and try to cool the person down while waiting for help by moving them to a cool place, removing extra clothing and applying cold water or ice packs.

To stay safe during the heat, officials recommend:

• Drinking water often, before feeling thirsty
• Closing blinds and turning on air conditioning or fans, or moving to a cooler space such as a cooling centre, library or shaded park
• Scheduling outdoor activities during the coolest parts of the day
• Wearing lightweight, light-coloured, loose-fitting clothing and a wide-brimmed hat
• Never leaving people or pets inside a parked vehicle

Montrealers without air conditioning can visit one of the city’s cooling centres, pools or splash pads. A list of locations is available on the City of Montreal’s website.

READ MORE: Where to cool off in Montreal: every public pool, wading pool and splash pad, mapped

- With files from The Canadian Press