Avg High
Ottawa in September
Avg Low
Rain
Daylight
13h
What to expect
September in Ottawa is early autumn, a shoulder-season window, so you can get a bit of variety across the month. The month is mostly mild for steady exploring, with a noticeable cool-down after sunset. Most days feel close to what the averages suggest, with straightforward pacing. The daylight window is balanced for full days without endless late evenings.
September in context
How it compares to the rest of the year in Ottawa.
Hottest (avg)
#4 / 12
Wettest (avg)
#5 / 12
Daylight Hours
#6 / 12
Windiest (avg)
#9 / 12
Highest UV
#6 / 12
Most Humid
#5 / 12
Monthly climate breakdown
Temperature
- Daytime high
-
- Nighttime low
-
- Feels like (avg)
-
Sunshine
- Daylight hours
- 12.5 h
- UV index (max)
- 6
- Typical sun hours
- 05:41 - 18:12
Rain & Snow
- Total rain
-
- Rainy days
- 12 days
- Cloud cover (avg)
- 56%
Humidity & Wind
- Humidity (avg)
- 76%
- Wind (avg)
-
- Wind (max gusts)
-
Daily climate explorer
Day 15 selected for September. Typical high 19.8°C and low 11.4°C.
Typical disruptions in September
Based on 30 years of historical data, these are the disruption patterns most likely to affect plans in September.
Rain High impact
Rain disruption Measures: Likely rain disruption days. Observed about 19% of days (5.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
5.6 days / month
~19% of days
Why this matters
- Expected days 5.6 days / month
- Probability ~19% of days
- Intensity Up to ~35mm (P95)
Rain disruption risk appears on ~6 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Washout risk Measures: Washout day risk. Observed about 18% of days (5.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
5.3 days / month
~18% of days
Why this matters
- Expected days 5.3 days / month
- Probability ~18% of days
- Intensity Up to ~37mm (P95)
Washout conditions are possible on ~5 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Heavy rain days Measures: Heavy rain days (>=10mm). Observed about 10% of days (2.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
2.9 days / month
~10% of days
Why this matters
- Expected days 2.9 days / month
- Probability ~10% of days
- Intensity Up to ~44mm (P95)
Heavy rain is possible on ~3 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Strong gusts Measures: Strong gust days (>=60 km/h). Observed about 4% of days (1.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.1 days / month
~4% of days
Why this matters
- Expected days 1.1 days / month
- Probability ~4% of days
- Intensity Up to ~87km/h (P95)
Strong gusts are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Wind High impact
Stormy conditions Measures: Storm-impact proxy days. Observed about 3% of days (0.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.9 days / month
~3% of days
Why this matters
- Expected days 0.9 days / month
- Probability ~3% of days
- Intensity Up to ~88km/h (P95)
Stormy conditions are possible on ~1 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Cold Moderate
Cold feels-like nights Measures: Cold feels-like nights (min <=5C). Observed about 9% of days (2.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
2.7 days / month
~9% of days
Why this matters
- Expected days 2.7 days / month
- Probability ~9% of days
- Intensity Up to ~5°C (P95)
Cold feels-like nights are possible on ~3 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Show all disruptions (21 more)
Rain High impact
Washout run Measures: Multi-day washout runs. Observed about 1.2 days/month in September. Historical risk signal only, not a day-by-day forecast.
1.2 days / month
Probability unavailable
Why this matters
- Expected days 1.2 days / month
- Probability —
- Intensity Up to ~32mm (P95)
Multi-day washout runs are possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain High impact
Very heavy rain Measures: Very heavy rain days (>=25mm). Observed about 2% of days (0.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.7 days / month
~2% of days
Why this matters
- Expected days 0.7 days / month
- Probability ~2% of days
- Intensity Up to ~50mm (P95)
Very heavy rain is possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind High impact
Severe gusts Measures: Severe gust days (>=80 km/h). Observed about 1% of days (0.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.2 days / month
~1% of days
Why this matters
- Expected days 0.2 days / month
- Probability ~1% of days
- Intensity Up to ~93km/h (P95)
Severe gusts are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Visibility Moderate
Fog-likely signal Measures: Fog-likely visibility proxy. Observed about 5% of days (1.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.4 days / month
~5% of days
Why this matters
- Expected days 1.4 days / month
- Probability ~5% of days
- Intensity Up to ~97% (P95)
Fog-likely conditions are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Moderate
Hot feels-like days Measures: Hot feels-like days (>=32C). Observed about 2% of days (0.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.6 days / month
~2% of days
Why this matters
- Expected days 0.6 days / month
- Probability ~2% of days
- Intensity Up to ~35°C (P95)
Feels-like heat >=32C is possible on ~1 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Humidity Moderate
Muggy days Measures: Muggy days (dew point >=20C). Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.5 days / month
~2% of days
Why this matters
- Expected days 0.5 days / month
- Probability ~2% of days
- Intensity Up to ~22°C (P95)
Muggy conditions are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Cloud Minor
Cloudy days Measures: Cloudy days (cloud cover >=60%). Observed about 48% of days (14.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
14.5 days / month
~48% of days
Why this matters
- Expected days 14.5 days / month
- Probability ~48% of days
- Intensity Up to ~100% (P95)
Cloudy skies are possible on ~14 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet days Measures: Wet days (>=0.1mm). Observed about 47% of days (14.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
14.1 days / month
~47% of days
Why this matters
- Expected days 14.1 days / month
- Probability ~47% of days
- Intensity Up to ~25mm (P95)
Measurable rain is possible on ~14 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Rainy hours Measures: Rain-hours signal (>=3h rain). Observed about 36% of days (10.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
10.9 days / month
~36% of days
Why this matters
- Expected days 10.9 days / month
- Probability ~36% of days
- Intensity Up to ~19h (P95)
Several rainy hours are possible on ~11 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Humidity Minor
High humidity Measures: High humidity days (RH >=80%). Observed about 30% of days (9.1 days/month) in September. Historical risk signal only, not a day-by-day forecast.
9.1 days / month
~30% of days
Why this matters
- Expected days 9.1 days / month
- Probability ~30% of days
- Intensity Up to ~95% (P95)
High humidity is possible on ~9 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 30% of days (8.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
8.9 days / month
~30% of days
Why this matters
- Expected days 8.9 days / month
- Probability ~30% of days
- Intensity Up to ~69km/h (P95)
Gusty conditions are possible on ~9 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Cloud Minor
Mostly cloudy days Measures: Mostly cloudy days (cloud cover >=80%). Observed about 26% of days (7.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
7.9 days / month
~26% of days
Why this matters
- Expected days 7.9 days / month
- Probability ~26% of days
- Intensity Up to ~100% (P95)
Mostly cloudy skies are possible on ~8 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Rain Minor
Wet most of day Measures: Wet-most-of-day signal (>=6h rain). Observed about 26% of days (7.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
7.7 days / month
~26% of days
Why this matters
- Expected days 7.7 days / month
- Probability ~26% of days
- Intensity Up to ~20h (P95)
Wet-most-of-day conditions are possible on ~8 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). Observed about 12% of days (3.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
3.5 days / month
~12% of days
Why this matters
- Expected days 3.5 days / month
- Probability ~12% of days
- Intensity Up to ~100% (P95)
Overcast skies are possible on ~4 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Humidity Minor
Humid days Measures: Humid days (dew point >=18C). Observed about 6% of days (1.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.7 days / month
~6% of days
Why this matters
- Expected days 1.7 days / month
- Probability ~6% of days
- Intensity Up to ~21°C (P95)
Humid conditions are possible on ~2 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Other Minor
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data Measures: Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data. Observed about 5% of days (1.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
1.4 days / month
~5% of days
Why this matters
- Expected days 1.4 days / month
- Probability ~5% of days
- Intensity Up to ~97 (P95)
Low visibility proxy: same as fog-likely (RH ≥90% AND cloud ≥95%) — true visibility requires hourly visibility data is possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Humidity Minor
Convective risk Measures: Convective storm risk proxy. Observed about 2% of days (0.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.6 days / month
~2% of days
Why this matters
- Expected days 0.6 days / month
- Probability ~2% of days
- Intensity Up to ~22°C (P95)
Convective risk signal appears on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Hot days Measures: Hot days (>=30C). Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.5 days / month
~2% of days
Why this matters
- Expected days 0.5 days / month
- Probability ~2% of days
- Intensity Up to ~33°C (P95)
Hot days are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Cold Minor
Cold nights Measures: Cold nights (min <=5C). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
0.3 days / month
~1% of days
Why this matters
- Expected days 0.3 days / month
- Probability ~1% of days
- Intensity Up to ~5°C (P95)
Cold nights are possible on ~0 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Heat Minor
Feels-like heatwave Measures: Feels-like heatwave runs (>=3 days). Observed about 0.1 days/month in September. Historical risk signal only, not a day-by-day forecast.
0.1 days / month
Probability unavailable
Why this matters
- Expected days 0.1 days / month
- Probability —
- Intensity Up to ~35°C (P95)
Feels-like heatwave runs are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Heat Minor
Heatwave run Measures: Heatwave runs (>=3 hot days). Observed about 0.1 days/month in September. Historical risk signal only, not a day-by-day forecast.
0.1 days / month
Probability unavailable
Why this matters
- Expected days 0.1 days / month
- Probability —
- Intensity Up to ~32°C (P95)
Heatwave runs are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Frequently asked questions
Is September a good time to visit Ottawa?
Typical September days in Ottawa reach highs of 21°C (70°F) with nights around 12°C (54°F). It usually feels mild by day and cool after dark. Overall, September sits in the middle of the Ottawa climate range.
What are temperatures like in September?
In September, you can usually expect highs of 21°C (70°F) and lows near 12°C (54°F). That means mild days and cool nights, so pack layers you can add or remove.
How much does it rain in September?
Rainfall in September averages 92 mm (3.6 in) across roughly 12 days. Overall it is a quite rainy time of year, so a light rain jacket and waterproof shoes are very handy.
How many hours of daylight are there in September?
You can expect about 13 hours of daylight in September. Sunrise is typically around 05:41 and sunset near 18:12. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are moderate (around 6); sunscreen and sunglasses are still a good idea.
Is it windy in September?
In September, average wind speeds are around 10 km/h (6 mph), with gusts on the windiest days reaching about 50 km/h (31 mph). On the ground, it is it often feels breezy, especially in more exposed spots or along the coast.