Weather in Calgary in September

Prime time. If you get to pick your dates, September is the one. Highs average 18.9 °C, lows 5.9 °C, and rain falls on 9 days — nothing in the month is working against you.

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

Rain on 9 days, 1 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 31.9 °C and the coldest night fell to -9 °C, and the wettest single day dropped 39 mm — roughly 74% 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 87 mm against 7 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 53 mm average is a reasonable planning figure, not a promise.

Wind is light at 3.6 km/h, so the temperature on the page is close to the temperature on your skin, and humidity is unremarkable at 67%.

How September sits in the year

The month is on the way down: 5.3 °C cooler than August, with October dropping another 7.6 °C. The first week and the last are not the same trip.

Daylight in September

12.7 hours of daylight, losing 1.9 hours across the month. That is between Calgary's extremes of 16.5 and 8 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 35 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage. At 1048 m the air is thin enough to matter — sun that burns faster than the temperature suggests, and nights that cool off quickly.

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 Calgary versus nearby

If Calgary is one option among several, the nearby comparison is worth making. Banff is the weaker option in September — 3.6 °C cooler, 6 days more rain. Lethbridge is close enough to be a coin toss — 2 °C warmer, 1 day less rain.

So: September is effectively as good as it gets here — 2 points behind August, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Calgary

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