WEATHER · CLIMATE NORMALS · 1991–2020
Ottawa Climate — Averages by Month
What the weather in Ottawa, CAaverages across a standard 30-year period. Each month's figure is the 1991–2020 mean temperature and total rainfall from the ERA5 reanalysis — the long-run normal a place settles around, not a forecast for any particular day.
Month-by-month normals
| Month | Avg temperature | Avg rainfall |
|---|---|---|
| January | -10.0 °C · coldest | 79.4 mm |
| February | -8.4 °C | 63.0 mm |
| March | -2.6 °C | 76.7 mm |
| April | 5.6 °C | 93.2 mm |
| May | 13.3 °C | 92.7 mm |
| June | 18.1 °C | 102.0 mm |
| July | 20.5 °C · warmest | 101.9 mm |
| August | 19.3 °C | 94.1 mm |
| September | 14.9 °C | 97.2 mm |
| October | 8.0 °C | 102.7 mm · wettest |
| November | 1.4 °C | 87.7 mm |
| December | -5.3 °C | 85.9 mm |
How to read these numbers
These are reanalysis normals, not readings from a single weather station. They come from the ERA5 0.25° (~25 km) global reanalysis grid, sampled at the grid cell nearest Ottawa — centred at 45.50°N, 75.75°W. A reanalysis blends observations with a physics model onto an even grid, so a coastal or mountain city's cell can read a little cooler, warmer, wetter or drier than the city centre itself. The month-to-month shape — when it's hot, when it rains — is what these normals capture best.
“Normal” means the 1991–2020 average, the current World Meteorological Organization standard period. A normal is what a place tends toward over decades — any single day, month or year can and will depart from it.