Photo: P199 · CC BY-SA 3.0Winter nights in Sarnia are milder than in 83% of Canadian towns
The warmest part of a July day comes in at 26.5°C on average. By July afternoons alone, it runs hotter than 65% of Canadian towns. Expect the most rain and snow in June and the least in February. From June to September, highs of 22–27°C make it easy to spend the day outdoors.
1991–2020 normals from ECCC’s Sarnia station, 4.4 km east.
A year in Sarnia at a glance
Each month’s typical high and low, in °C.
What stands out about Sarnia’s climate
Compared with Canadian towns, with its place among towns of 2,500+ in Ontario beside it.
What a year in Sarnia feels like
Seasons and months as ECCC’s 1991–2020 normals give them: a typical day’s high and low.
131 frost days and 124 days above 20°C a year
Frost comes from October to April; in January almost every night freezes. About 15 days a year top 30°C.
Frost days by month
Average days at 0°C or below
Days above 20°C by month
Average days
About 871 mm of rain and snow a year
About 113 days a year bring 1 mm or more.
Rain and snow by month
Millimetres
Rain alone by month
Millimetres
112 cm of snow in a typical year
From November to April snow is likely; January is the peak, at about 34 cm.
Snowfall by month
Centimetres
Snow on the ground by month
Centimetres at month’s end
Heating a home in Sarnia
92% of a year’s heating need falls between October and April. Months averaging under 10°C: November to April.
Think of it as a year’s worth of daily shortfalls below 18°C, added up. By this count, homes here need less heating than 86% of Canadian towns.
Living with Sarnia’s climate
The averages read for the garden, the outdoors and the coldest and hottest days.
The comfortable months for a day outside, highs of 17–27°C and nights of 8°C or more: Jun, Jul, Aug and Sep.
Parks & trails →Expect around 14 days a year when the wind chill sinks below −20.
Storms, floods and heat waves sit outside these normals; Sarnia’s hazards page covers them.
Flood & hazards →ECCC’s normals location: Sarnia
ECCC builds the Sarnia normals from 4 stations’ records over 1991–2020, joined where one replaced another.
| Distance from the town | 4.4 km east |
| Station altitude | 181 m |
| Completeness | meets the WMO “3 and 5” rule |
| WMO standard normals | No |
| Coldest reading, 1991–2020 | −28.0°C |
| Hottest reading, 1991–2020 | 37.9°C |
| Average wind | 15.0 km/h on average, most often from the south |
| Next-nearest location | Strathroy-Mullifarry, 58 km |
How Sarnia compares
Placed among 2,611 Canadian towns and neighbourhoods of 2,500+, each on its nearest normals location; each dot is another location used in Ontario.
Nearby towns’ climate
The nearest places on a normals location of their own: those that share Sarnia’s would only repeat its figures. Sarnia has few close neighbours with figures, so the list reaches 40–49 km out.
| Town | July high | January low | Rain & snow |
|---|---|---|---|
| Sarnia | 26.5°C | −8.2°C | 871 mm |
| Watford 40 km · Strathroy-Mullifarry | 27.3°C 0.8°C warmer | −8.5°C about the same | 966 mm |
| Dawn-Euphemia 41 km · Ridgetown | 27.2°C 0.7°C warmer | −8.2°C about the same | 903 mm |
| Walpole Island 46 49 km · Windsor Riverside | 29.2°C 2.7°C warmer | −6.3°C 1.9°C milder | 935 mm |
Sarnia weather by month
Average daily high and low, mean temperature, rain and snow (as water) and snowfall by month, 1991–2020.
| Month | High | Low | Mean | Rain & snow | Snow |
|---|---|---|---|---|---|
| January | −0.9°C | −8.2°C | −4.6°C | 57 mm | 34 cm |
| February | 0.0°C | −7.9°C | −4.0°C | 48 mm | 20 cm |
| March | 5.0°C | −3.7°C | 0.6°C | 57 mm | 22 cm |
| April | 11.9°C | 1.5°C | 6.7°C | 79 mm | 4 cm |
| May | 18.7°C | 7.4°C | 13.1°C | 85 mm | 0 cm |
| June | 24.0°C | 13.0°C | 18.6°C | 93 mm | 0 cm |
| July | 26.5°C | 16.0°C | 21.3°C | 80 mm | 0 cm |
| August | 25.5°C | 15.3°C | 20.4°C | 71 mm | 0 cm |
| September | 22.2°C | 11.3°C | 16.7°C | 84 mm | 0 cm |
| October | 15.4°C | 6.0°C | 10.7°C | 78 mm | 1 cm |
| November | 8.0°C | 0.4°C | 4.2°C | 80 mm | 7 cm |
| December | 2.1°C | −4.4°C | −1.2°C | 60 mm | 25 cm |
| Year | 13.2°C | 3.9°C | 8.5°C | 871 mm | 112 cm |
February strays furthest from its normal year to year, by 2.9°C; June the least
March has the widest record range, −22.3°C in 2003 to 27.9°C in 2012; the tick on each bar is the month’s normal.
Where Sarnia’s numbers come from
Averages over 30 years, not a forecast.
- Normals: the 1991–2020 Canadian Climate Normals at Sarnia, the closest ECCC location with twelve months of temperature normals.
- Comparisons: a pool of Canadian towns and neighbourhoods of 2,500 or more, read alike; whole cities and reserves stay out of it.
- Not on this page: hours of sunshine, missing from the 1991–2020 normals, and a height correction: the town has no elevation on file.
Canadian Climate Normals 1991–2020 · ECCC Data Services End-use Licence. Data Source: Environment and Climate Change Canada
Questions about Sarnia’s climate
How warm does Sarnia get in summer?
Of all twelve months, July has the warmest afternoons, about 26.5°C.
How cold does Sarnia get in winter?
Expect nights around −8.2°C in January; no month is colder.
How much rain and snow does Sarnia get?
The yearly total is about 871 mm. June gets 93 mm, the most of any month; February gets 48 mm, the least.
Are these figures for Sarnia itself?
Yes. They were measured in Sarnia, at ECCC’s own station there.
Data Source: Environment and Climate Change Canada · ECCC Data Services End-use Licence Today’s forecast for Sarnia →
Adapted from Statistics Canada (Census of Population 2021, population estimates 2025, 2021 census boundaries) under the Statistics Canada Open Licence; this does not constitute an endorsement by Statistics Canada. Neighbourhood names in some cities © OpenStreetMap contributors (ODbL).