Sarnia climate — normals and trends
Sarnia (Canada) has a hot-summer humid continental climate (Dfa) under the Köppen-Geiger classification. Its mean annual temperature is 8.8 °C and it receives 829 mm of precipitation per year.
These figures are normals computed over 86 complete calendar years, from 1940 to 2025, using ERA5 reanalysis data from the Copernicus programme.
The warmest month is July (22.1 °C on average) and the coldest is January (-4.7 °C). Rainfall peaks in May.
Sarnia averages 118 frost days, 8 hot days (≥ 30 °C) and 125 rainy days per year.
Sarnia has warmed by +1.7 °C between 1940 and 2025, or +0.20 °C per decade. This trend is statistically significant.
The number of frost days there went from about 132 to 104 per year over the period.
The hottest day of the period reached 37.1 °C (on 25 June 1988) and the coldest -27.0 °C (on 16 January 1994).
Data from ERA5 reanalysis (Copernicus Climate Change Service), redistributed under a CC-BY 4.0 licence. Normals are recomputed whenever the archive is updated.
Climate normals · ERA5
SarniaOntario
- coords
- 42.98°, -82.40°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
8.8°C
Average daily high
12.5°C
Average daily low
5.2°C
Annual rainfall
829mm
Sunshine / day
8.7h
Mean relative humidity
74%
Average peak wind
20.2km/h
Seasonal range
26.8°C
Frost days (< 0 °C)
118 d/yr
Hot days (≥ 30 °C)
8 d/yr
Rainy days (≥ 1 mm)
125 d/yr
Annual snowfall
87.6 cm
Average feels-like high
10.3 °C
Average feels-like low
2.1 °C
Average peak gust
39.4 km/h
Tropical nights (≥ 20 °C)
22 d/yr
Solar radiation
14.2 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+1.7 °C
since 1940
+0.2 °C per decade · r² = 0.34 · p = < 0.001
Trend fitted by linear regression (ordinary least squares) on annual means. A trend is shown only when it is statistically significant (p < 0.05).
A climograph overlays rainfall (bars) and temperature (line): the standard reading in climatology, where you can see at a glance whether the warm season is also the dry one.
Records for the period
Hottest day
37.1 °C
25 June 1988
Coldest day
-27.0 °C
16 January 1994
Wettest day
82 mm
25 June 1968
Windiest day
57.4 km/h
25 March 1947
Strongest gust
111.2 km/h
25 March 1947
Hottest feels-like
42.4 °C
14 July 1995
Coldest feels-like
-34.0 °C
4 January 1981
Snowiest day
30.1 cm
25 March 1947
Sunniest day
15.0 h
1 June 1940
Normals computed over complete calendar years 1940–2025.
A specific year
Pick a year and see how it compares to normal — warmer, drier or more extreme than usual?
Across the whole year
Month by month
| High | vs. normal | Precipitation | vs. normal | |
|---|---|---|---|---|
| Jan | -2.4 °C | -0.9 °C | 34 mm | -20 mm |
| Feb | -1.2 °C | -0.6 °C | 49 mm | -2 mm |
| Mar | 8.9 °C | +4.7 °C | 77 mm | +13 mm |
| Apr | 12.5 °C | +1.5 °C | 74 mm | -6 mm |
| May | 16.0 °C | -1.6 °C | 76 mm | -6 mm |
| Jun | 24.6 °C | +1.1 °C | 90 mm | +11 mm |
| Jul | 26.9 °C | +0.9 °C | 78 mm | +3 mm |
| Aug | 24.7 °C | -0.3 °C | 42 mm | -31 mm |
| Sep | 22.5 °C | +1.3 °C | 51 mm | -21 mm |
| Oct | 16.6 °C | +1.9 °C | 66 mm | -4 mm |
| Nov | 7.6 °C | 0.0 °C | 42 mm | -28 mm |
| Dec | 0.7 °C | -0.6 °C | 80 mm | +19 mm |
The year's extremes
What was the weather like that day?
Your birthday, a wedding, a memorable trip: discover the actual weather for any date since 1940.
Frequently asked questions
What is the climate of Sarnia?
Sarnia has a hot-summer humid continental climate (Köppen Dfa). Over 1940-2025, the average annual temperature is 8.8 °C and it receives 829 mm of precipitation per year.
What is the hottest day ever recorded in Sarnia?
The hottest day measured in Sarnia between 1940 and 2025 was 25 June 1988, reaching 37.1 °C.
What is the coldest day in Sarnia?
The coldest day measured in Sarnia between 1940 and 2025 was 16 January 1994, at -27.0 °C.
Does it snow in Sarnia?
Yes. Sarnia gets on average 87.6 cm of snow per year and has around 118 frost days.
Has the climate of Sarnia warmed?
Yes: Sarnia warmed by +1.7 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Sarnia?
The wettest day measured in Sarnia between 1940 and 2025 was 25 June 1968, with 82 mm of rain in 24 hours.
What was the windiest day in Sarnia?
The windiest day measured in Sarnia between 1940 and 2025 was 25 March 1947, with winds reaching 57.4 km/h.
What is the warmest month in Sarnia?
The warmest month in Sarnia is July (22.1 °C on average); the coldest is January (-4.7 °C).
How much does it rain in Sarnia?
Sarnia receives on average 829 mm of precipitation per year, spread over about 125 rainy days.
Is it sunny in Sarnia?
Sarnia gets on average 8.7 hours of sunshine per day, roughly 3,175 hours per year over 1940-2025.
What is the biggest single-day snowfall in Sarnia?
The heaviest 24-hour snowfall measured in Sarnia between 1940 and 2025 was 25 March 1947, with 30.1 cm.
Are there tropical nights in Sarnia?
Yes: Sarnia has on average 22 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Sarnia?
In Sarnia, between 1940 and 2025, the highest apparent temperature reached 42.4 °C on 14 July 1995, and the lowest was -34.0 °C on 4 January 1981.
Compare Sarnia with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Sarnia