Cornwall climate by month
What the weather is like
Cornwall has a warm-summer humid continental climate (Köppen Dfb): warm summers, cold winters and precipitation in every season.
The warmest month is July, when afternoons average 23° and nights 16°. February is the coolest month, with highs of -3° and lows of -10°. The difference between the warmest and the coolest month is about 26°, a large swing typical of continental interiors.
About 1,242 mm of precipitation falls in an average year. December is the wettest month (124 mm, 16 wet days) and September the driest (107 mm, 10 wet days). Cloud cover ranges from 36% in August to 56% in December.
The sea reaches about 19° in August. Sea temperatures lag the air by a month or two, so late summer is usually warmer for swimming than early summer.
Compared with Ottawa, the capital, Cornwall is 3.9° cooler on a July afternoon and receives more precipitation over the year.
Year in figures
- Hottest afternoons
- 23° · July
- Coldest nights
- -10° · February
- Wettest month
- December
- Driest month
- September
- Clearest skies
- August · 36% cloud
- Warmest sea
- 19° · August
- Longest day
- 15 h 46 min
- Shortest day
- 8 h 38 min
Twelve months at a glance
Temperature and precipitation
Daily high/low range bars, monthly precipitation columns, sea temperature lineTemperature curve
Average high, low and seaDaylight
Hours between sunrise and sunset on the 15th of each monthClimate normals month by month
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Average high | -3° | -3° | 1° | 7° | 14° | 19° | 23° | 23° | 19° | 13° | 7° | 1° |
| Average low | -10° | -10° | -6° | 0° | 6° | 11° | 16° | 16° | 12° | 7° | 1° | -5° |
| Precipitation | 108 mm | 84 mm | 92 mm | 92 mm | 97 mm | 102 mm | 89 mm | 98 mm | 107 mm | 127 mm | 122 mm | 124 mm |
| Wet days (≥1 mm) | 14.8 | 11.7 | 14.3 | 12.5 | 14 | 14.8 | 15.3 | 11.5 | 10.3 | 13 | 14.8 | 15.5 |
| Cloud cover | 54% | 49% | 47% | 49% | 45% | 41% | 38% | 36% | 38% | 44% | 52% | 56% |
| Sea temperature | 0° | -1° | -1° | 1° | 5° | 11° | 17° | 19° | 17° | 13° | 8° | 2° |
| Daylight | 9h 01 | 10h 22 | 11h 52 | 13h 33 | 14h 58 | 15h 46 | 15h 26 | 14h 11 | 12h 35 | 10h 58 | 9h 27 | 8h 38 |
| Month score | 15 | 23 | 18 | 21 | 38 | 62 | 64 | 70 | 72 | 36 | 16 | 14 |