Monthly climate averages for Cornwall, Canada. Based on 10-year ERA5 reanalysis data.
Dfa Hot-Summer Continental
Climate OverviewCornwall, Canada in September has warm conditions, with highs averaging 21.8°C (71°F).
This month falls at the beginning of Autumn.
Daily highs in September gradually drop from around 23°C (74°F) at the start to 20°C (67°F) by month's end.
Rainfall is heaviest during the last third of the month, while the middle tends to be drier.
Expect around 9.7h of sunshine at the start of September, decreasing to 8.6h by the end.
The warmest days tend to fall around the 4th, averaging 23.5°C (74°F).
Compared to August, this month is about 4°C cooler with 5 fewer rainy days. Temperatures begin dropping heading into October.
Daily averages based on historical data (2016–2025)
Daytime temperatures around 22°C (71°F) are ideal for full-day outdoor exploration.
Rain usually comes in shorter passing showers rather than all-day rain.
Recent yearly records for September have stayed close to the long-run average.
| Month | Temp | Feels Like | Rain | Sun | Humidity | UV | Status | Details |
|---|---|---|---|---|---|---|---|---|
| January | -2°C / -10°C | -7°C / -15°C | 12days (80 mm) Wet | 4.9h Fair | 77% Humid | 1.9 Low | Poor | View Details |
| February | 0°C / -10°C | -5°C / -15°C | 13days (82 mm) Wet | 6h Fair | 75% Muggy | 2.9 Moderate | Poor | View Details |
| March | 4°C / -5°C | 0°C / -9°C | 13days (90 mm) Wet | 7.4h Good | 72% Muggy | 4 Moderate | Poor | View Details |
| April | 11°C / 2°C | 8°C / -2°C | 13days (115 mm) Wet | 8.3h Good | 68% Muggy | 4.7 Moderate | Poor | View Details |
| May best | 19°C / 9°C | 18°C / 6°C | 12days (90 mm) Wet | 10.2h Excellent | 69% Muggy | 5.6 High | Good | View Details |
| June best | 24°C / 14°C | 25°C / 13°C | 13days (104 mm) Wet | 10.8h Excellent | 71% Muggy | 6.1 High | Excellent | View Details |
| July best | 27°C / 18°C | 28°C / 18°C | 12days (112 mm) Wet | 11.9h Excellent | 74% Muggy | 6.6 High | Excellent | View Details |
| August best | 25°C / 17°C | 27°C / 18°C | 13days (115 mm) Wet | 10.6h Excellent | 76% Humid | 5.7 High | Excellent | View Details |
| September best | 22°C / 14°C | 22°C / 13°C | 8days (68 mm) Wet | 9.3h Good | 76% Humid | 4.8 Moderate | Excellent | View Details |
| October | 15°C / 8°C | 13°C / 5°C | 13days (130 mm) Wet | 6.6h Fair | 76% Humid | 3.1 Moderate | Fair | View Details |
| November | 6°C / 0°C | 3°C / -4°C | 13days (92 mm) Wet | 5.1h Fair | 77% Humid | 2 Low | Poor | View Details |
| December | 1°C / -5°C | -3°C / -10°C | 13days (90 mm) Wet | 4.2h Fair | 77% Humid | 1.5 Low | Poor | View Details |
Dress in layers — a mix of long sleeves, light sweaters, and a versatile jacket works best for changeable conditions.
A waterproof jacket or compact umbrella is recommended for occasional showers.
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