Climate averages 1991–2020
Sarnia weather
in September.
A mild, moderately wet month: the 4th warmest and the 8th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a mild month in Sarnia: daytime highs average 21.7°C and nights cool to about 14.7°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 73 mm of rain on roughly 9 days, which makes September a moderately wet month (the 8th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 33 min on an average September day.
The nearest other city in this atlas is Clinton Township (61 km away). In September its highs average 22.1°C, about as warm as Sarnia, with 67 mm of rain.
Among the 86 cities listed in Canada, Sarnia ranks 3rd of 86 for the warmest September highs and joint 22nd of 86 for the driest September (rainfall, lowest first). The mean September high of those 86 cities is 19.8°C; Sarnia is 1.9°C warmer than that mean.
From September to October, average highs fall by 6.9°C to 14.7°C, and monthly rainfall rises from 73 mm to 76 mm.
The annual picture
September in context
Monthly precipitation
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Sarnia climate table
| Month | Average highHigh / low | Average low | Precipitation mm/month | Wet days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | -1.2°C-7.8°C | -7.8°C | 57 | 9.6 | 9.49 h |
| February | -0.3°C-8.0°C | -8.0°C | 52 | 8.4 | 10.510 h |
| March | 4.6°C-3.7°C | -3.7°C | 57 | 9.6 | 11.912 h |
| April | 11.4°C2.8°C | 2.8°C | 85 | 11.4 | 13.413 h |
| May | 18.3°C9.7°C | 9.7°C | 85 | 12.0 | 14.615 h |
| June | 23.7°C15.9°C | 15.9°C | 87 | 10.7 | 15.315 h |
| July | 26.1°C18.8°C | 18.8°C | 71 | 11.0 | 15.015 h |
| August | 25.2°C18.3°C | 18.3°C | 70 | 10.4 | 13.914 h |
| September, selected | 21.7°C14.7°C | 14.7°C | 73 | 9.1 | 12.513 h |
| October | 14.7°C8.5°C | 8.5°C | 76 | 10.8 | 11.111 h |
| November | 7.7°C2.2°C | 2.2°C | 66 | 9.7 | 9.810 h |
| December | 1.8°C-3.3°C | -3.3°C | 56 | 9.4 | 9.19 h |
Precipitation (rain or snow, as water) is the average of the 30 separate monthly totals. A wet day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Clinton Township in SeptemberUnited States · 61 kmHigh 22.1°C · Low 14.8°C · 67 mm rain
- Shelby in SeptemberUnited States · 62 kmHigh 22.1°C · Low 14.3°C · 72 mm rain
- Sterling Heights in SeptemberUnited States · 68 kmHigh 22.3°C · Low 14.6°C · 67 mm rain
- Rochester Hills in SeptemberUnited States · 70 kmHigh 22.0°C · Low 14.0°C · 75 mm rain
- Warren in SeptemberUnited States · 74 kmHigh 22.4°C · Low 14.3°C · 67 mm rain
- Troy in SeptemberUnited States · 74 kmHigh 22.1°C · Low 14.2°C · 70 mm rain
- Southfield in SeptemberUnited States · 87 kmHigh 22.4°C · Low 14.2°C · 70 mm rain
- Waterford in SeptemberUnited States · 88 kmHigh 22.0°C · Low 13.6°C · 73 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Sarnia) is explained once on the Sarnia year overview and on the Sources, method and limits page.