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Ottawa Weather in September
September is one of the excellent months to visit Ottawa, with daytime temperatures of 22°C (72°F) and lows of 10°C (50°F) at night. Do note that quite a bit of rainfall is typical, averaging around 99 mm (3.9 in).
Rainfall in Ottawa in September
Looking at the last 30 years, the data shows about 12 days with rain, averaging 99 mm (3.9 in) for the month. When it rains this month, it tends to come down fairly heavily. Showers can be substantial even if they don't last all day.
Temperature in Ottawa in September
The temperature in Ottawa in September is excellent. Daytime highs reach 22°C (72°F), with nights dropping to 10°C (50°F). Conditions stay fairly consistent through the month, making it easier to plan what to wear. With lows around 10°C (50°F), nights are cold. The upside is that cool, crisp nights are often the best for a deep sleep.
Sunshine in Ottawa in September
With about 178 hours of sunshine, the area enjoys a nice balance of sun and overcast, creating a pleasant environment.Our weather planner can help you find worldwide destinations with pleasant weather during this period. May, August and September typically offer the best weather for Ottawa.
Ottawa Temperature in September
Min Temperature
10°C (50°F)
Max Temperature
22°C (72°F)
Chance of Rain
40%
Precipitation
99 mm (3.9 in)
Rainy days
12 days
Humidity
59%
Sunshine
178 hours
Percentage Sunshine
47%
Ottawa Weather by Month
Pick a month to see the average temperature, rainfall and sunshine in Ottawa - and find the best time to visit.
Daily Historical Temperatures
50-year average (1976-2025)
Based on our historical records, temperatures in Ottawa typically drop from around 23°C (73°F) at the start of September to approximately 18°C (64°F) by the end. Nights are cool, with lows typically ranging from 6°C (43°F) to 12°C (54°F).
Average temperatures in September
Daily Historical Precipitation
50-year average (1976-2025)
Average daily rainfall for each day of the month based on long-term records.
Average precipitation in September
Historical weather records for Ottawa in September
Browse day-by-day weather records for Ottawa spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.
Ottawa historical weather extremes in September
According to our 49 years of weather records for Ottawa, the following extremes were recorded between 1976 and 2025.
- Ottawa recorded its highest September temperature of 35°C (95°F) on September 9, 2002.
- The coldest night in September in Ottawa was on September 29, 1980, with a minimum of -3°C (27°F).
Best Places in Canada in September
Find out more about the weather in Canada and which places have the best travel conditions in this month. See all of Canada in September →
perfect weather
pleasant
tolerable
unpleasant
poor
Perfect weather is subjective. On this map perfect weather has been defined with temperatures between 20°C (68°F) and 29°C (84°F) and not too much precipitation (less than 90 mm (3.5 in) a month).
What to Wear in Ottawa in September
Pleasant temperatures in September mean you can pack light but flexibel pieces. Think cotton t-shirts, comfortable walking shorts, and one warmer layer for evenings. A light sweater or denim jacket works well. Prepare for significant rainfall with proper waterproof clothing and shoes. Sunglasses could come in handy during the sunnier parts of your trip.
What To Do in Ottawa in September
We rated the following activities from 1 (least suitable) to 10 (best) to do.
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Swimming6/10 -
Cycling9/10 -
Walking9/10 -
Camping4/10 -
Outdoor sports9/10
Ottawa 3-Day Forecast
More climate data for Ottawa
Temperature Rainfall Sunshine Humidity
See the full Ottawa climate overview or explore weather in Canada.
Popular in September
Where to go in September - average daytime high across popular destinations.
Toronto
22°C (72°F) Niagara Falls23°C (73°F) Montréal
22°C (72°F) Ottawa22°C (72°F) Quebec City
20°C (68°F) Vancouver19°C (66°F) Calgary19°C (66°F) Whistler15°C (59°F) Bucket list
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