By Julia · weather-canada.com editorial team · Published · 4 min read
Anyone who has lived in Calgary will tell you the January forecast can swing by twenty degrees in a day. The usual explanation is the chinook, a warm, dry wind that comes down the eastern slopes of the Rockies. A reanalysis like ERA5 does not label chinooks, and this article does not claim to spot any single one. It asks something simpler: in ten years of daily data, how large are the swings on the prairies, and does Calgary really stand apart?
Fourteen days in January 2018
Start with a stretch where the answer is visible by eye.
CalgaryEdmontonWinnipeg
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editorial team.
On December 31, 2017, Calgary's daily high is −28.8 °C, the end of a cold spell that is part of the outbreak described in the article on cold snaps. On January 1 the high is −4.1 °C: a jump of 24.7 degrees in one day, the biggest one-day change in Calgary's November-to-March record for 2016–2025. For the next eight days the highs stay between −1.8 and 3.5 °C, the peak coming on January 6. On January 9 the high is −1.8 °C, on January 10 it is −17.9 °C, and on January 11 it is −22.6 °C. By January 13 it is +2.6 °C again.
Edmonton follows almost the same script, from −23.0 °C on December 31 to −5.4 °C on January 1 and −23.9 °C on January 11. Winnipeg misses the first thaw: its highs stay between −20 and −9 °C until January 6, then touch about zero from January 7 to 10. So in this fortnight the warm spell was an Alberta-wide event with a different timing in Manitoba, not something that belongs to Calgary alone. That is worth knowing before attributing every winter thaw to a chinook.
Where Calgary does stand apart
The picture changes when you count, rather than pick the dramatic days.
| City | Days per winter above 0 °C | Days per winter at 5 °C or more | Average one-day change in the high (degrees) | Highest winter high (°C) |
|---|---|---|---|---|
| Calgary | 44.7 | 15.4 | 3.8 | 15.1 |
| Edmonton | 26.4 | 2.8 | 3.8 | 10.6 |
| Winnipeg | 15.5 | 1.3 | 4.1 | 9.2 |
| Toronto | 57.3 | 18.6 | 3.2 | 16.3 |
| Vancouver | 86.3 | 61.3 | 1.4 | 14.3 |
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editorial team.
Between December and February, Calgary has on average 44.7 days a winter with a high above freezing, Edmonton 26.4 and Winnipeg 15.5. At 5 °C or more the gap is wider: 15.4 days in Calgary, 2.8 in Edmonton, 1.3 in Winnipeg. Toronto, with a far milder January, has 18.6 days at 5 °C or more, so Calgary's count falls just over three days short of Toronto's. Calgary also holds the warmest winter high of the group with 15.1 °C, reached on February 26, 2016. Edmonton's best was 10.6 °C and Winnipeg's 9.2 °C.
CalgaryEdmontonWinnipeg
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editorial team.
The pattern repeats in every winter of the series. Calgary had between 11 and 25 days at 5 °C or more, and the 25 came in 2021–22. Edmonton never exceeded 8, Winnipeg never 7. The winter of 2023–24 was exceptional for all three: 19 days in Calgary, 8 in Edmonton, 7 in Winnipeg.
But the swings are not unique to Calgary
If chinooks made Calgary swing more, the average change from one day's high to the next would be larger there than elsewhere. It is not. Across December to February the mean one-day change in the daily high is 3.8 degrees in Calgary, 3.8 in Edmonton, 4.1 in Winnipeg, 3.2 in Toronto and 1.4 in Vancouver. The prairies are all jumpy; what sets Calgary apart is the ceiling, how often the jump lands above freezing. Winnipeg's average swing is larger, but it swings between cold and colder.
| Day | High the day before (°C) | High that day (°C) | Change (degrees) |
|---|---|---|---|
| Jan 1, 2018 | −28.8 | −4.1 | 24.7 |
| Jan 13, 2018 | −18.1 | 2.6 | 20.7 |
| Feb 20, 2025 | −16.8 | 3.7 | 20.5 |
| Dec 2, 2024 | −16.6 | 3.9 | 20.5 |
| Feb 28, 2024 | −14.4 | 5.6 | 20.0 |
| Dec 18, 2022 | −3.2 | −22.5 | −19.3 |
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editorial team.
Five of the six biggest one-day jumps in Calgary's November to March record are rises, the largest being the 24.7 degrees of January 1, 2018 and the smallest a rise of 20.0 degrees, from −14.4 to 5.6 °C, on February 28, 2024. The sixth is a fall of 19.3 degrees, from −3.2 to −22.5 °C, on December 18, 2022.
January is a lottery
A last way to see the variance is the mean temperature of January itself.
| Year | Calgary | Edmonton | Winnipeg |
|---|---|---|---|
| 2016 | −7.3 | −10.6 | −14.6 |
| 2017 | −8.5 | −9.9 | −12.9 |
| 2018 | −7.0 | −10.4 | −12.5 |
| 2019 | −3.5 | −8.3 | −17.1 |
| 2020 | −9.6 | −14.1 | −12.3 |
| 2021 | −4.9 | −8.0 | −8.5 |
| 2022 | −6.8 | −10.7 | −18.7 |
| 2023 | −5.0 | −7.7 | −11.6 |
| 2024 | −10.3 | −13.3 | −10.5 |
| 2025 | −5.7 | −7.9 | −15.3 |
Open-Meteo, ERA5 archive, 2016–2025 (reanalysis, not a weather station); calculation by the editorial team.
Calgary's Januaries run from −10.3 °C in 2024 to −3.5 °C in 2019, a gap of nearly 7 degrees. Edmonton's range from −14.1 °C in 2020 to −7.7 °C in 2023. Winnipeg's gap is the widest, 10 degrees, between −18.7 °C in 2022 and −8.5 °C in 2021. A resident who plans for "a typical January" will be wrong most years.
What to do with it
Dress in layers that open as well as close: the temperature can be −20 °C in the morning and above zero by the afternoon. In Calgary, a thaw followed by a refreeze turns melt into ice on roads and sidewalks, so a fresh round of cold after a mild spell deserves more caution than the mild spell itself. And treat the average winter as a useless planning figure on the prairies. The range, as shown in this article and in the one on wind chill, is the thing to prepare for.
Period of the data cited: 2016–2025.