Ottawa in September
In September, Ottawa averages 21°C (70°F) during the day and 13°C (55°F) at night, with frequent rain — about 15 days of the month see precipitation (78 mm total).
High seasonConditions are comfortable for sightseeing without being sweltering. Plan for unsettled weather and bring rain gear.
September offers comfortable temperatures in Ottawa, with some rain to plan around.
How September compares to the rest of the year in Ottawa
September is in the middle of the year for warmth in Ottawa (4th of 12) and one of the driest months (12th of 12). Daytime temperature runs 10°C above the annual average (12°C). September runs 4°C cooler than August (25°C) and cools 7°C in October (14°C).
September sunrise & sunset in Ottawa
Times shown for Ottawa local time (America/Toronto), calculated for the 15th of September. They shift by a few minutes day to day across the month.
Photography light in Ottawa — September
Golden-hour and blue-hour windows for the 15th of September, in Ottawa's local time. Use these for soft warm light (golden) or cool architectural twilight (blue).
📅 When to book — Ottawa in September
Travel writers usually only tell you when to go. Here's when to book flights and lodging for the best mix of price and availability, based on September's tier (High season) and Ottawa's popularity.
Crowds & pricing — September in Ottawa
This is a busy month in Ottawa — not the absolute peak, but tourist numbers are clearly elevated. You'll feel it at headline attractions on weekends and in the historic centre, though side streets and lesser-known sights stay manageable. Prices are above off-season but not at their summit. A good week for first-time visitors who want everything open without the worst of the crush.
Why this tier: excellent tourism weather
Sun & mosquito risk — September in Ottawa
UV is a clear-sky sea-level estimate — clouds, altitude, and reflective surfaces (snow, water) shift it ±30%. Mosquito risk is climate-derived only; for current disease advisories (dengue, malaria, zika) check the CDC or WHO travel pages before your trip.
Ottawa in other months
| Month | Avg high | Avg low | Rainfall | Rain days | Snow days |
|---|---|---|---|---|---|
| January | -4°C / 24°F | -14°C / 7°F | 73 mm | 18 | — |
| February | -3°C / 26°F | -13°C / 9°F | 77 mm | 17 | — |
| March | 2°C / 36°F | -7°C / 19°F | 78 mm | 18 | — |
| April | 11°C / 51°F | 0°C / 32°F | 117 mm | 17 | — |
| May | 19°C / 67°F | 8°C / 46°F | 73 mm | 16 | — |
| June | 24°C / 74°F | 13°C / 56°F | 119 mm | 18 | — |
| July | 26°C / 79°F | 17°C / 62°F | 100 mm | 18 | — |
| August | 25°C / 77°F | 16°C / 62°F | 108 mm | 18 | — |
| September | 21°C / 70°F | 13°C / 55°F | 78 mm | 15 | — |
| October | 14°C / 57°F | 6°C / 44°F | 115 mm | 18 | — |
| November | 5°C / 42°F | -1°C / 30°F | 74 mm | 17 | — |
| December | 0°C / 32°F | -7°C / 20°F | 83 mm | 17 | — |
Other cities with similar September weather
🌍 See the full ranked list of climate twins for Ottawa in September →
Frequently asked questions
How hot is Ottawa in September?
In September, Ottawa averages a high of 21°C (70°F) and a low of 13°C (55°F) — generally mild and pleasant.
Does it rain a lot in Ottawa in September?
September is quite rainy in Ottawa, with about 15 rainy days on average.
Is September a good time to visit Ottawa?
September is mild and pleasant but on the rainy side. It suits travelers who are comfortable with mild and pleasant weather; check the month-by-month ranking to compare it against the rest of the year.
What should I pack for Ottawa in September?
Pack light layers for warm days and cooler evenings, plus a compact umbrella or rain jacket. See the full September packing list for Ottawa for a complete, climate-based checklist.
Check the live 10-day forecast and sunrise/sunset.