Ontario and Quebec Heat Dome: What Residents, Employers, and Caregivers Should Do as Records Fall and Power Grids Strain

What This Means for You

If you live anywhere from southwestern Ontario through eastern Quebec, you are inside one of the most dangerous weather events Canada faces in the warm months: a stalled high-pressure system that pushes daytime highs toward 36°C, drives humidex values into the 42–46°C range, and stresses the same electricity grid you need to cool your home. The 2026 heat dome already broke June 23 daily temperature records in Toronto, Ottawa, and Montreal, according to Environment Canada, and storms tied to the same system left tens of thousands of customers without power across Ontario and Quebec. Based on our analysis of the 2021 British Columbia heat dome — which killed 619 people in British Columbia, the vast majority indoors and over 70 years of age — the next 48 hours are when the most preventable deaths happen, and the actions you take today are the ones that matter most.

Here is the expert guidance you need, broken down by household situation.

If You Have a Vulnerable Family Member (Over 65, Living Alone, on Medication, or with a Chronic Condition):

Set up a phone-check schedule today, not tomorrow

The 2021 BC coroner's review found that the single biggest predictor of heat-related death was social isolation. People who lived alone, did not have a daily check-in, and did not have working air conditioning died at far higher rates than people in identical apartments with daily contact. If you have an elderly parent, sibling, or neighbour in Toronto, Hamilton, Kingston, Ottawa, Montreal, Laval, or anywhere in the heat dome, set a twice-daily phone call — morning and late afternoon — for the next four days.

What to listen for on the call:

Confusion, slurred speech, or unusual irritability (early signs of heat stroke).
Reports of headache, nausea, or "feeling weak" (heat exhaustion).
"I turned off the AC because I was cold" — a common and dangerous signal of heat-stroke confusion.
Long pauses, missed words, or inability to answer simple orientation questions.

If you hear any of these signs, do not wait for a callback the next day. Call 911 or a relative who can physically check on them within the hour.

Medication considerations during extreme heat

Many common medications interact badly with heat. According to public health guidance from Health Canada and provincial heat-vulnerability protocols, the high-risk classes include:

Diuretics (cause dehydration faster).
Beta-blockers (blunt the body's heart-rate response to heat).
Anticholinergics (reduce sweating).
Antipsychotics and SSRIs (impair temperature regulation).
Lithium (toxicity risk rises with dehydration).

If your family member takes any of these, encourage them to drink fluids on a schedule (not based on thirst), keep medications out of direct sunlight, and call their pharmacist if they feel unusually unwell.

Get them into air conditioning if their home has none

Every major Ontario and Quebec city has opened emergency cooling centres. Toronto, Montreal, Ottawa, and Gatineau have publicly listed centres at municipal libraries, community centres, and pools. Drive or pay for a taxi to get a vulnerable family member to a cooled space if they do not have AC at home. The cost of a return Uber to a library beats the cost of an ambulance call by an order of magnitude — and it works.

Example scenario: A 78-year-old widow in a non-air-conditioned third-floor Toronto apartment with hypertension medication is the textbook 2021-BC fatality profile. Her adult children, even if they live in Calgary, can keep her alive this week by: (1) calling at 9 a.m. and 5 p.m. every day, (2) arranging a neighbour to physically check on her at 2 p.m. (the daily peak), (3) paying for an Uber to the Toronto Reference Library or any cooled space for the afternoon, and (4) confirming she has at least one room with a working AC unit or a window-fan setup with damp towels.

If You Are an Employer with Outdoor Workers:

Adjust shifts before the heat warning expires, not after

Ontario's Occupational Health and Safety Act and Quebec's CNESST regulations both require employers to protect workers from heat stress. The practical compliance threshold during a humidex 40+ event is to shift outdoor work to early morning (before 10 a.m.) or evening (after 6 p.m.), provide shaded rest areas, and mandate water breaks every 15 to 20 minutes. The current heat warning is forecast to lift on Wednesday, according to Environment Canada, but it is best practice to keep adjusted scheduling through Thursday because the heat-stress risk lingers in the body even after temperatures fall.

Practical employer checklist for the next 48 hours:

Move any non-emergency outdoor work to before 10 a.m. or after 6 p.m.
Provide cold water (not just lukewarm) at the work site. Coolers with ice, not just bottles in a truck.
Build in 15-minute rest breaks in shade or AC every hour during humidex 40+ conditions.
Pair workers — never have a single worker alone in heat-stress conditions.
Train supervisors to recognize the difference between heat exhaustion (pale, sweating, dizzy — get into shade, hydrate) and heat stroke (red, dry skin, confused, hot to touch — call 911 immediately).

Liability note: If a worker collapses from heat stress and the employer did not adjust schedules during a posted Environment Canada heat warning, both provincial OHS regulators and personal injury counsel will use the warning as documentary evidence of foreseeability. The compliance cost of adjusting schedules is far lower than the WSIB or CNESST claim cost.

If You Are a Renter Without Air Conditioning:

Use the "swamp cooler" emergency stack, in order

Renters in older Toronto, Hamilton, and Montreal apartments often face the worst of heat domes: brick buildings that absorb daytime heat and release it slowly all night. Without central AC, the order of operations matters.

Close blinds and curtains during the day, especially on south- and west-facing windows. This can drop indoor temperature by 3–5°C.
Block direct sunlight at the window with a sheet or aluminum foil if you have no blinds. It looks bad; it works.
Use a window fan blowing outward in the warmest room during the day to push hot air out. Reverse it after sunset to pull cooler outside air in.
Hang damp sheets in front of any open window or fan at night. The evaporation cools the incoming air.
Sleep in the lowest, coolest room. Basements are 5–8°C cooler than upper floors.
Wet your wrists, neck, and ankles with cold water every 20 minutes when actively trying to cool down.

If your landlord is not maintaining basic habitability: Toronto's vital service maintenance bylaws and the Quebec Civil Code both treat dangerous heat in rental units as a habitability issue. Document the indoor temperature with a photo of a thermometer for at least three consecutive days, file a complaint with Toronto 311 or the Régie du logement equivalent, and request urgent intervention. Toronto's "extreme heat" complaint pathway has been used successfully against landlords whose units sustained indoor temperatures over 31°C for multiple days.

The News: What Happened

According to CBC News and the Globe and Mail, a heat dome — a high-pressure system that traps hot air over a region — settled over Ontario and Quebec beginning Sunday, June 21, 2026 and is expected to persist until Wednesday, June 24. Environment Canada meteorologist Steven Flisfeder told reporters that Toronto, Ottawa, and Montreal were among the cities to set new June 23 daily temperature records, with Toronto reaching 36°C at Pearson airport late Monday afternoon and breaking a record set in 1983.

Global News reports that the heat warning extends from southwestern Ontario north to Sudbury and Timmins, and from Montreal to Shawinigan and north to Abitibi in Quebec. Humidex values are forecast to peak between 42 and 46°C.

According to Radio-Canada, severe thunderstorms tied to the same weather system knocked out power to more than 38,000 customers in and around Quebec City by 12:30 p.m. on Tuesday. As of 3:17 p.m. EDT on June 23, approximately 17,500 Ontario homes and businesses were without power, with Hydro One reporting 12,314 outages and additional disruptions from Niagara Peninsula Energy and Hydro Ottawa, according to local utility data.

CTV News reports that Environment Canada has issued heat warnings across most of the affected region, with daytime highs of up to 36°C and overnight lows that fail to provide meaningful cooling — a key risk factor for heat-related illness.

Analysis: Why This Matters

Based on our analysis of the 2021 BC heat dome and the 2018 Quebec heat wave (which killed 90 people, primarily in Montreal), this event has the same epidemiological signature as the deadliest indoor heat events in Canadian history: prolonged daytime highs above 35°C, humidex above 40°C, overnight lows that do not fall below 22°C, and a major urban population with a meaningful share of older adults in non-air-conditioned housing. The 2018 Montreal heat wave killed people primarily inside low-rise apartments without central AC, and the 2021 BC heat dome killed people primarily inside houses where windows had been left closed and fans were used incorrectly. Both events were preventable — public health investigations afterward identified social isolation and lack of AC access as the two biggest fatal factors.

Historical Context:

Canada has experienced increasingly frequent heat domes over the last decade — including the 2021 BC event, the 2018 Quebec heat wave, and the 2024 Ontario humidex spike. Public-health authorities have responded by lowering heat-warning thresholds, opening cooling centres earlier, and improving outreach to seniors. The infrastructure response has lagged: most Ontario and Quebec rental stock built before 1990 was not designed for sustained 35°C interior conditions.

What Happens Next:

The heat dome is forecast to break by Wednesday evening or Thursday morning as cooler air pushes in from the northwest, according to Environment Canada. Expect: continued power outages as transformers fail from prolonged load, scattered severe thunderstorms as the system breaks, a tail of heat-related emergency room visits that typically peaks 24–48 hours after the temperature itself peaks, and a wave of municipal post-event reviews focused on cooling-centre access and senior outreach.

Your Action Plan

Immediate (Today and Tomorrow):

Call any family member over 65 who lives alone — twice today.
Confirm at least one room in your home stays below 26°C — relocate sleeping to that room.
Identify the nearest cooling centre and library hours.
Stock 4 litres of cold water per person for the next 48 hours.

Short-term (This Week):

If you are an employer with outdoor workers, formally adjust shifts for the heat warning period.
If you are a renter without AC, document indoor temperatures with timestamped photos.
If you have pets, never leave them in a parked vehicle, even briefly.

Long-term (This Year):

Apply for the Canada Greener Homes Loan if a heat pump (which is also AC) would help your household.
Sign up for Environment Canada's WeatherCAN heat-alert push notifications.
If you rent, ask your landlord in writing about AC plans before next summer.

Other Perspectives

Environment Canada:

Meteorologist Steven Flisfeder told media that the heat dome would last "a few more days," with Toronto, Ottawa, and Montreal breaking June 23 records, according to CBC News reporting.

Public Health Authorities:

Toronto Public Health, Santé publique de Montréal, and Ottawa Public Health have all activated their heat response protocols. According to Global News, these protocols include extended cooling-centre hours, outreach calls to registered vulnerable residents, and enhanced ambulance staffing.

Utilities:

Hydro One, Hydro-Québec, and local distribution companies are reporting elevated outage volumes. According to Radio-Canada, Hydro-Québec attributed the Quebec City-area outages to severe thunderstorms tied to the heat dome, not to load shedding.

Heat-Vulnerability Advocates:

Groups including the Canadian Public Health Association have for years called for more aggressive cooling-centre access, mandatory AC in subsidized housing, and rental-code reforms. The Globe and Mail reports that advocates are once again raising these issues as the 2026 heat dome unfolds.

Note: Including multiple perspectives doesn't imply all views are equally valid, but ensures readers can make informed judgments.

Corrections Policy

We strive for accuracy. If you find an error in this analysis, please email us at [email protected]. We will promptly investigate and correct any factual inaccuracies.

Updates:

No corrections to date (as of June 23, 2026)