Weather in Ottawa in May

A good month. May is a solid month to be in Ottawa. Highs average 18.7 °C, lows 6.8 °C, and rain falls on 14 days — nothing in the month is working against you.

May ranks 3 of 12 in Ottawa. Only September scores clearly higher, and the difference is small enough to be settled by price rather than weather.

This is persistent light rain rather than storms: 14 wet days but only 2 heavy ones. It rarely cancels anything outright, and it rarely fully clears either. A jacket beats an umbrella. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average May reaches 30 °C. Across the twenty years measured, the hottest May day reached 31.2 °C and the coldest night fell to -4 °C, and the wettest single day dropped 42 mm — roughly 49% of the month's rain in one day.

May is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest May on record still delivered 175 mm against 43 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 85 mm average is a reasonable planning figure, not a promise.

Wind is light at 1.2 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 77%, high enough to notice on the warm days without dominating them.

How May sits in the year

The month is on the way up: 7.6 °C warmer than April, and June adds another 4.6 °C. Late in the month feels noticeably different from the start of it, which is worth knowing if the trip is short.

Daylight in May

14.9 hours of daylight, gaining 1.2 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.

May in Ottawa versus nearby

If Ottawa is one option among several, the nearby comparison is worth making. Kingston is the weaker option in May — 3.5 °C cooler, 1 day more rain. Montréal is the weaker option in May — within a degree on temperature, 1 day more rain.

So: May is effectively as good as it gets here — 6 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 May.