Weather in Montréal in September

Prime time. If you get to pick your dates, September is the one. Highs average 21.3 °C, lows 10.2 °C, and rain falls on 11 days — nothing in the month is working against you.

September is the highest-scoring month of the twelve. The nearest rival is August, and the month at the other end of the year is December.

Rain on 11 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 September day reached 33 °C and the coldest night fell to -0.4 °C, and the wettest single day dropped 63 mm — roughly 72% of the month's rain in one day.

September is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest September on record still delivered 168 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 9.4 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 75%, high enough to notice on the warm days without dominating them.

How September sits in the year

The month is on the way down: 3.6 °C cooler than August, with October dropping another 8.9 °C. The first week and the last are not the same trip.

Daylight in September

12.6 hours of daylight, losing 1.6 hours across the month. That is between Montréal's extremes of 15.7 and 8.7 hours, so days are long enough not to constrain the plan.

An inland climate

Montréal has no sea to moderate it, and it shows: 43.1 °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.

September in Montréal versus nearby

If Montréal is one option among several, the nearby comparison is worth making. Sherbrooke is close enough to be a coin toss — within a degree on temperature, 3 days more rain. Ottawa is close enough to be a coin toss — within a degree on temperature, 1 day more rain.

So: September is the answer for Montréal. If it is booked out or priced out, August is the next best thing at 5 points behind, and December is the month to keep off the shortlist.

Every month in Montréal

See all twelve months in Montréal, or where else to go in September.