By Julia · weather-canada.com editorial team · Published · 4 min read
A Winnipeg afternoon at 33 °C and a Toronto afternoon at 33 °C are not the same afternoon. The difference is water vapour, and Canada has a number for it: the humidex, which combines temperature and dew point into the temperature it feels like. According to the Canadian Centre for Occupational Health and Safety, 30 to 39 means some discomfort, 40 to 45 great discomfort where exertion should be avoided, and 46 and over is dangerous, with heat stroke possible.
This article uses two kinds of data. Humidex values are those published by Environment and Climate Change Canada (ECCC) for each city's airport station, hour by hour, from 2016 to 2025. The 30 °C counts and warm-night counts come from the ERA5 reanalysis at the city centre. The two sources are never mixed in one figure, and the reanalysis is not a station.
Two thermometers, two summers
Start with a gap. From May to September, ERA5 gives Ottawa 12.3 days a year at 30 °C or more, Winnipeg 11.3, Toronto 7.5, Montréal 5.3, Calgary 5.1 and Vancouver 1.1. But on the humidex, Toronto reaches 30 on 66.7 days a summer, Montréal on 62.2, Ottawa on 60.8 and Winnipeg on 45.6. A humidex of 30 is reached four to twelve times as often as an air temperature of 30 °C.
| City | Humidex 30+ (days) | 40+ (days) | 46+ (days) | Highest hourly humidex and date |
|---|---|---|---|---|
| Toronto | 66.7 | 6.2 | 0.2 | 46 · Jun 30, 2018 |
| Montréal | 62.2 | 5.0 | 0.0 | 45 · Jul 1, 2018 |
| Ottawa | 60.8 | 5.9 | 0.3 | 47 · Jul 1, 2018 |
| Winnipeg | 45.6 | 2.3 | 0.1 | 46 · Jul 17, 2022 |
| Halifax | 40.5 | 1.0 | 0.0 | 42 · Jul 21, 2019 |
| Vancouver | 12.4 | 0.1 | 0.0 | 40 · Jun 28, 2021 |
| Calgary | 11.8 | 0.0 | 0.0 | 37 · Jun 28, 2021 |
| Edmonton | 18.0 | 0.3 | 0.0 | 44 · Jul 10, 2024 |
Environment and Climate Change Canada, hourly observations at each city's airport station (MSC GeoMet, climate-hourly), 2016–2025; wind chill and humidex as published by ECCC; counts by the editorial team.
The table above shows how the cities line up. At the great-discomfort level, 40 or more, Toronto has 6.2 days a summer, Ottawa 5.9, Montréal 5.0 and Winnipeg 2.3. Halifax has 1.0, Edmonton 0.3, Vancouver 0.1 and Calgary none in ten years. The 46 and over rung appears only in Toronto, Ottawa and Winnipeg, at 0.2, 0.3 and 0.1 days a year, which is one to three days in a decade.
The warm east, the dry middle
Ottawa has more days above 30 °C than Toronto, but Toronto has more humid days: its humidex of 30 or more is more frequent, and its nights are warmer. In the reanalysis, Toronto has 14.5 nights a summer with a minimum of 20 °C or more between June and August, against 7.9 in Ottawa, 6.8 in Montréal and 4.5 in Winnipeg. That is the number that decides sleep.
Winnipeg is the clearest case for the dry-heat side. Its 30 °C days are nearly as many as Ottawa's, and in 2021 the reanalysis counts 27 of them between May and September, the most of any year in the four cities charted below. Yet its humidex of 40 or more occurs on 2.3 days a summer, because the prairie air is drier. When Winnipeg does get both, it is serious: its highest humidex in the ten years is 46, on July 17, 2022.
TorontoOttawaWinnipegVancouver
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editorial team.
Peaks: the highest hourly humidex per station
- Ottawa, 47, July 1, 2018.
- Toronto, 46, June 30, 2018.
- Winnipeg, 46, July 17, 2022.
- Montréal, 45, July 1, 2018.
- Edmonton, 44, July 10, 2024.
- Halifax, 42, July 21, 2019.
- Vancouver, 40, June 28, 2021, and Calgary, 37, the same day.
The date pattern is telling. Three of the top peaks fall on June 30 and July 1, 2018, in Toronto, Ottawa and Montréal. Vancouver and Calgary share a June 28, 2021 peak, and the reanalysis agrees: June 28, 2021 is also Vancouver's hottest day in the daily series, at 36.4 °C. Edmonton's 44 in July 2024 is a reminder that prairie cities can reach humid heat when the dew point rises.
Episodes, not days
Humidex of 40 or more rarely arrives alone. Grouping days within two days of each other across Toronto, Montréal, Ottawa and Winnipeg gives clear episodes.
| Period | Cities at humidex 40 or more | City-days at 40 or more | Highest hourly humidex and city |
|---|---|---|---|
| Jun 30 – Jul 2, 2018 | Toronto, Montréal, Ottawa | 9 | 47 · Ottawa |
| Jul 7 – Jul 10, 2020 | Toronto, Montréal, Ottawa | 10 | 43 · Ottawa |
| Jul 24 – Jul 27, 2020 | Toronto, Montréal, Ottawa, Winnipeg | 8 | 43 · Winnipeg |
| Aug 9 – Aug 16, 2021 | Toronto, Montréal, Ottawa, Winnipeg | 9 | 41 · Toronto |
| Aug 6 – Aug 8, 2022 | Toronto, Montréal, Ottawa | 7 | 43 · Toronto |
| Sep 4 – Sep 6, 2023 | Toronto, Montréal, Ottawa | 7 | 42 · Toronto |
| Jun 18 – Jun 20, 2024 | Toronto, Montréal, Ottawa | 8 | 44 · Toronto |
| Aug 1 – Aug 3, 2024 | Montréal, Ottawa, Winnipeg | 7 | 41 · Ottawa |
Environment and Climate Change Canada, hourly observations at each city's airport station (MSC GeoMet, climate-hourly), 2016–2025; wind chill and humidex as published by ECCC; counts by the editorial team.
The longest stretch in the data is August 9 to 16, 2021, with humidex at 40 or more in at least one city on six of the eight days. The highest peak is in the spell of June 30 to July 2, 2018, when three cities were at 40 or more and Ottawa reached 47. In the table, only the eight episodes with the most city-days are listed. Several others, such as June 22 to 24, 2025, with Toronto at 46, came close.
TorontoMontréalOttawaWinnipeg
Environment and Climate Change Canada, hourly observations at each city's airport station (MSC GeoMet, climate-hourly), 2016–2025; wind chill and humidex as published by ECCC; counts by the editorial team.
Year to year, the count moves a lot. Toronto had 11 days at 40 or more in 2018 and 10 in 2025, but only 1 in 2017 and 3 in each of 2019 and 2023. Ottawa had 11 in 2025 and 10 in 2018. Winnipeg never exceeded 4 in a summer. Do not plan a summer by the average: plan by the range.
What to do with the numbers
At a humidex of 30 to 39, which Toronto sees about two months a year, you need water and shade, not a plan. At 40 or more, move strenuous work and exercise to the morning or evening, and keep an eye on the person who does not look hot: older people, children, and anyone working in the heat. At 46 and over, the CCOHS wording is "dangerous". For the other summer hazard, which looks very different in the data, see wildfire smoke. For the temperature record of the decade, ten years of Canadian weather.
Period of the data cited: 2016–2025.