Weather in Ottawa in August

A good month. August is a solid month to be in Ottawa. Highs average 25.4 °C, lows 14.7 °C, and rain falls on 14 days — nothing in the month is working against you.

August ranks 2 of 12 in Ottawa. Only September scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 14 days, 3 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

The averages here are honest — no hidden extremes worth planning around. Across the twenty years measured, the hottest August day reached 34.6 °C and the coldest night fell to 6.8 °C, and the wettest single day dropped 42 mm — roughly 48% of the month's rain in one day.

August is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest August on record still delivered 140 mm against 37 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 88 mm average is a reasonable planning figure, not a promise.

Wind is light at 1 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 78%, high enough to notice on the warm days without dominating them.

How August sits in the year

Temperatures hold steady either side: 26 °C in July, 25.4 here, 21.9 in September. Nothing about the timing within the month matters much.

Daylight in August

14.2 hours of daylight, losing 1.4 hours across the month. That is between Ottawa's extremes of 15.6 and 8.8 hours, so days are long enough not to constrain the plan.

An inland climate

Ottawa has no sea to moderate it, and it shows: 42.4 °C separates the hottest afternoon of the year from the coldest night. That is a genuinely continental range, and it means summer and winter here are barely the same place.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

August in Ottawa versus nearby

If Ottawa is one option among several, the nearby comparison is worth making. Kingston is close enough to be a coin toss — within a degree on temperature, the same number of rain days. Montréal is close enough to be a coin toss — within a degree on temperature, the same number of rain days.

So: August is effectively as good as it gets here — 4 points behind September, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Ottawa

See all twelve months in Ottawa, or where else to go in August.