Last updated: April 22, 2025
September in Ottawa, Canada, showcases dynamic weather as it transitions from the warmth of summer to the crispness of fall. With maximum temperatures reaching a soaring 32°C (90°F), and an average of 15°C (60°F), the month often presents pleasantly warm days. However, the temperature can drop to a minimum of 0°C (31°F), reminding residents that autumn is near. Rainfall is frequent, with 79 mm (3.1 in) of precipitation spread across approximately 11 days, contributing to a relatively high humidity level of 72%. This mix of temperatures and moisture creates a vibrant atmosphere, making September a unique time to experience Ottawa’s evolving landscape.
As September unfolds in Ottawa, Canada, the temperatures provide a gentle transition from the warmth of summer to the crispness of fall. The month greets residents with a minimum temperature of 0°C (32°F) and an average of 15°C (60°F), setting the stage for a refreshing change. As the days progress, the mercury can climb to a pleasant 32°C (90°F) on warmer afternoons, echoing lingering summer vibes. However, a noticeable dip in nighttime temperatures marks the onset of autumn, reminding everyone that winter is just around the corner. Overall, September in Ottawa is characterized by a delightful blend of warm days and cool evenings, making it an ideal time for outdoor activities amid the changing foliage.
In September, Ottawa experiences a gentle transition into autumn, marked by an average precipitation of 79 mm (3.1 in) over 11 days. This volume is modest compared to the heavier rainfall seen in the spring and summer months, while still maintaining a significant presence in the weather pattern. The decline from the summer peak of 114 mm in July showcases a subtle shift as the city prepares for the vibrant fall foliage ahead. Despite this decrease, September remains wetter than the winter months, indicating a lingering summer influence before the more pronounced autumn weather settles in. The combination of milder temperatures and sporadic rainfall creates a refreshing and rejuvenating atmosphere, perfect for enjoying the early signs of fall.
As summer transitions into fall, September in Ottawa experiences a noticeable shift in humidity, settling at 72%. This figure reflects a moderate drop from the higher levels of August, which averaged around 67%, yet remains elevated compared to the earlier spring months. The pattern reveals that while humidity typically peaks during the winter months — soaring to 93% in January and February — September marks a more comfortable phase. Following the drier summer, the humidity begins to creep back up, hinting at the approaching chill of October, where levels are projected to rise to 83%. This gradual fluctuation in humidity not only influences the local climate but also sets the stage for the vibrant autumn scenery that Ottawa is renowned for.
As September rolls into Ottawa, the UV Index drops to a moderate high of 7, signaling a shift from the peak summer levels. This marks a transition from the intense very high readings experienced in July and August, where the burn time was a mere 15 minutes. With a burn time now extending to 25 minutes, residents can enjoy the outdoors while still being mindful of sun exposure. This month reflects a gradual cooling trend, but protective measures are still important as the UV Index remains significant. For comprehensive information on UV levels throughout the year, check the Ottawa UV Index.
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As the summer fades and autumn begins, September in Ottawa welcomes a bountiful 267 hours of sunshine, marking a beautiful transition from the vibrant days of July and August. This month retains a significant share of sunlight, showcasing a noteworthy dip from the previous peaks but still well above the winter months that follow. After enjoying the longest days of the year, September offers a gentle reminder of the changing seasons, allowing residents to savor mild weather and stunning fall foliage. The sunlight hours start to decline, but September's brilliance still reflects the resilience of summer's warmth, creating an inviting atmosphere in the capital as it prepares for the cozy embrace of autumn.
September in Ottawa experiences a 39% chance of sunny weather, revealing a trend of increasing sunshine as summer transitions into autumn. This month stands out among the cooler fall months, showcasing a notable increase from the gloomier January and February, which linger around 27% to 35%. Interestingly, September's sunshine probability is also slightly higher than the summer months of July and June, where the chances hover around 34% and 35%. With this promising percentage, September offers a delightful opportunity for residents and visitors alike to revel in the lingering warmth of summer while enjoying the beautiful fall foliage that begins to emerge.
As summer transitions to fall in Ottawa, Canada, September brings a notable shift in daylight hours, offering around 12 hours of sunlight. This month serves as a bridge between the long, sun-drenched days of summer, which peak at 15 hours in June and July, and the more subdued hours of autumn, where daylight decreases to 10 hours by October. The gradual tapering of sunlight in September signifies not only the change in seasons but also invites Ottawans to savor the remaining warmth before winter's approach. The rhythmic ebb and flow of daylight throughout the year highlights the city's dynamic climate and the beauty of each seasonal transition.
In September, Ottawa experiences a pleasant shift in the air, with an average wind speed of 3.0 m/s (7 mph), offering a refreshing welcome after the stillness of summer. This gentle breeze marks a slight increase compared to the slower winds of August, where the average dipped to 2.4 m/s (5 mph). As summer transitions to autumn, the winds begin to pick up, outpacing the previous months, where July and August saw the calmest conditions. Interestingly, September's wind speed mirrors that of November, hinting at a trend where the fall months bring back a more invigorating atmosphere as nature gears up for the winter chill. This moderate wind not only enhances the beauty of the changing leaves but also invites outdoor enthusiasts to enjoy the crisp air and the vibrant scenery of the city.
The weather in Ottawa changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of September's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in Ottawa and find detailed weather information for every month.
September and January present stark contrasts in weather. September experiences a wide temperature range with minimums around 0°C and maximums reaching up to 32°C, resulting in an average temperature of 15°C. The month receives approximately 79 mm of precipitation over 11 days and maintains a moderate humidity level of 72%. In contrast, January is characterized by frigid temperatures, with minimums plunging to -32°C and an average of -9°C, peaking at only 10°C. This winter month has slightly less precipitation at 76 mm, spread over fewer days (9 days), but higher humidity reaches 93%. For more details on January's weather, visit Ottawa weather in January.
When comparing the weather in September and February, the contrasts are striking. September experiences a wider temperature range, with minimums around 0°C (31°F) and maximums peaking at 32°C (90°F), averaging around 15°C (60°F). In contrast, February is characterized by much colder temperatures, with minimums dipping to -27°C (-16°F) and averages sitting at -8°C (18°F). Interestingly, both months receive similar levels of precipitation, with September at 79 mm (3.1 in) over 11 days and February slightly higher at 81 mm (3.2 in) over 12 days, though February's humidity is notably higher at 93%. For a closer look at what to expect, visit Ottawa weather in February.
September and March display markedly different weather conditions. In September, temperatures range from a chilly 0°C (31°F) to a warm 32°C (90°F), with an average of 15°C (60°F). The month sees around 79 mm (3.1 in) of precipitation over approximately 11 days, with a humidity level of 72%. In contrast, March experiences much colder temperatures, ranging from a minimum of -24°C (-12°F) to a maximum of 20°C (69°F), with an average temperature of -3°C (27°F). Although March has slightly higher precipitation at 87 mm (3.4 in), it occurs over 12 days, and the humidity is notably higher at 86%. For a more detailed look at March weather, you can visit Ottawa weather in March.
September and April present contrasting weather patterns. September enjoys a milder average temperature of 15°C (60°F), with highs reaching up to 32°C (90°F) and lows around 0°C (31°F). The month experiences moderate precipitation, averaging 79 mm (3.1 in) over 11 days, with humidity at 72%. In contrast, April is cooler on average, with temperatures ranging from a low of -12°C (10°F) to a high of 27°C (81°F), and an average temperature of only 5°C (42°F). This month sees slightly higher precipitation at 112 mm (4.4 in) over 12 days and increased humidity at 82%. For a detailed look at April weather specifics, check out Ottawa weather in April.
In September, temperatures in Ottawa typically range from a minimum of 0°C (31°F) to a maximum of 32°C (90°F), with an average temperature of 15°C (60°F). This month sees approximately 79 mm (3.1 in) of precipitation spread over 11 days, accompanied by a humidity level of 72%. In contrast, May experiences slightly cooler temperatures with a minimum of -3°C (26°F) and an average of 13°C (56°F), while reaching a maximum of 35°C (95°F). May is also wetter, with 117 mm (4.6 in) of precipitation over 14 days and a marginally higher humidity of 75%. For a more detailed look at May's weather patterns, visit Ottawa weather in May.
In comparing the weather between September and June, we find that both months experience a similar maximum temperature of 32°C (90°F in September and 91°F in June), but their overall climate characteristics differ. September shows a broader range with minimum temperatures dipping as low as 0°C (31°F), while June starts slightly warmer at a minimum of 2°C (36°F). Average temperatures are also more moderate in June at 18°C (65°F) compared to September's 15°C (60°F). Additionally, September sees a bit more rainfall with 79 mm (3.1 in) over 11 days, while June has higher precipitation at 98 mm (3.9 in) over 13 days, accompanied by slightly lower humidity levels of 68% in June compared to 72% in September. For more detailed information, visit Ottawa weather in June.
When comparing the weather in September and July, September presents a wider temperature range with a minimum of 0°C (31°F) and a maximum of 32°C (90°F), averaging around 15°C (60°F). In contrast, July typically features milder conditions, with temperatures ranging from a minimum of 8°C (47°F) to a maximum of 35°C (96°F), and an average of 21°C (70°F). Rainfall in July is heavier at 114 mm (4.5 in) over 12 days, compared to September's 79 mm (3.1 in) spread across 11 days. Humidity levels are slightly higher in September at 72%, while July maintains a lower 69%. For more details on July weather, visit Ottawa weather in July.
In August, the weather is characterized by warmer temperatures, with a minimum of 7°C (45°F) and an average of 20°C (68°F), while September sees cooler nights with a minimum of 0°C (31°F) and an average of 15°C (60°F). Both months can experience peak temperatures reaching up to 32°C (90°F), but September tends to be slightly wetter, receiving 79 mm (3.1 in) of precipitation over 11 days compared to August's 94 mm (3.7 in) over 13 days. The humidity is also marginally higher in September at 72%, while August has a more comfortable level at 67%. For more detailed insights, you can check Ottawa weather in August.
In September, temperatures in Ottawa typically fluctuate from a chilly 0°C (31°F) at night to a warm 32°C (90°F) during the day, with an average of 15°C (60°F). The month sees about 79 mm (3.1 in) of precipitation over 11 days, accompanied by a humidity level of 72%. In contrast, October brings cooler temperatures, with lows dropping to -6°C (22°F) and an average of 9°C (48°F), while daytime highs reach up to 27°C (81°F). Precipitation increases to 132 mm (5.2 in) over 12 days, and humidity rises to 83%. For more detailed information, check out Ottawa weather in October.
September and November exhibit stark contrasts in weather. In September, temperatures typically range from a minimum of 0°C (31°F) to a maximum of 32°C (90°F), with an average of 15°C (60°F). The month sees approximately 79 mm (3.1 in) of precipitation over 11 days and a humidity level of 72%. In contrast, November experiences much colder temperatures, with a minimum of -19°C (-2°F) and an average of 0°C (33°F), peaking at a maximum of 22°C (71°F). Precipitation slightly increases to 97 mm (3.8 in), lasting over 14 days, coupled with higher humidity at 88%. For more details, you can check Ottawa weather in November.
September and December present starkly contrasting weather conditions. In September, temperatures range from a chilly 0°C (31°F) at night to a warm 32°C (90°F) during the day, with an average of 15°C (60°F). This month also sees moderate humidity at 72% and experiences 79 mm (3.1 in) of precipitation over 11 days. In contrast, December plunges into much colder territory, with temperatures varying from a frigid -29°C (-20°F) to a maximum of 14°C (58°F) and an average of -5°C (22°F). The humidity rises to 89%, and precipitation slightly increases to 80 mm (3.2 in) over 12 days. For more details, you can check Ottawa weather in December.
As summer transitions to fall, September in Ottawa showcases a unique blend of weather characteristics that set it apart from other months. With warm days peaking at 32°C (90°F) contrasted by cooler nights averaging around 15°C (60°F), temperatures can vary significantly. The city also experiences an uptick in rainfall, with 11 days of precipitation totaling 79 mm (3.1 in), contributing to the increased humidity level of 72%. This month is marked by a refreshing crispness in the air, making it an ideal time for outdoor activities amidst the beautiful autumn foliage. For a deeper understanding of how Ottawa’s weather evolves throughout the year, explore Ottawa Climate.