Hottest (avg)
#4 / 12
Sits around the middle of the year.
September in context
How it compares to the rest of the year in Denver.
Wettest (avg)
#8 / 12
Typical rainfall for the year.
Daylight Hours
#6 / 12
Around the yearly average.
Windiest (avg)
#10 / 12
Usually calmer than most months.
Highest UV
#6 / 12
Near the middle of the yearly UV range.
Most Humid
#11 / 12
One of the less humid months.
Monthly climate breakdown
A detailed look at the typical climate conditions for September.
Thermal profile
Temperature
Typical daytime high
- Nighttime low
-
- Feels like (avg)
-
Light window
Sunshine
12.4 h
Average daylight
- UV index (max)
- 7
- Typical sun hours
- 05:41 - 18:07
Wet-day pattern
Rain & Snow
Typical rainfall
- Rainy days
- 8 days
- Cloud cover (avg)
- 35%
- Snowfall
-
Air feel
Humidity & Wind
49%
Average humidity
- Wind (avg)
-
- Wind (max gusts)
-
Historical daily baseline
Daily climate explorer
Pick a day to inspect the usual conditions through September in Denver. Based on a 30-year historical climate baseline, not a forecast.
Primary control
Select a day
Scroll to compare daily conditions. The summary updates with your selection.
Secondary context
Monthly trend
Median daytime highs across the month, with a softer low line.
Median temperatureMedian lowTypical range
Day 15 selected for September. Temperature 25.6°C.
Historical disruption baseline
Typical disruptions in September
Based on 30 years of historical data, these are the disruption patterns most likely to affect plans in September.
Cold High impact
Cold feels-like nights Measures: Cold feels-like nights (min <=5C). Observed about 23% of days (7.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
7.0 days / month
- Share of days
- ~23% of days
- Upper edge
- Up to ~5°C (P95)
Why this matters
Cold feels-like nights are possible on ~7 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Heat High impact
Hot days Measures: Hot days (>=30C). Observed about 18% of days (5.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
5.5 days / month
- Share of days
- ~18% of days
- Upper edge
- Up to ~36°C (P95)
Why this matters
Hot days are possible on ~5 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Rain High impact
Washout risk Measures: Washout day risk. Observed about 7% of days (2.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.2 days / month
- Share of days
- ~7% of days
- Upper edge
- Up to ~23mm (P95)
Why this matters
Washout conditions are possible on ~2 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain Moderate
Rain disruption Measures: Likely rain disruption days. Observed about 7% of days (2.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.2 days / month
- Share of days
- ~7% of days
- Upper edge
- Up to ~23mm (P95)
Why this matters
Rain disruption risk appears on ~2 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Heat Moderate
Hot feels-like days Measures: Hot feels-like days (>=32C). Observed about 3% of days (0.8 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.8 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~35°C (P95)
Why this matters
Feels-like heat >=32C is possible on ~1 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 0.7 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.7 days / month
- Share of days
- —
- Upper edge
- Up to ~34°C (P95)
Why this matters
Heatwave runs are possible on ~1 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Show all disruptions (18 more)
Rain High impact
Washout run Measures: Multi-day washout runs. Observed about 0.5 days/month in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.5 days / month
- Share of days
- —
- Upper edge
- Up to ~22mm (P95)
Why this matters
Multi-day washout runs are possible on ~1 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 1% of days (0.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.2 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~73km/h (P95)
Why this matters
Strong gusts are possible on ~0 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain Moderate
Heavy rain days Measures: Heavy rain days (>=10mm). Observed about 3% of days (0.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.9 days / month
- Share of days
- ~3% of days
- Upper edge
- Up to ~24mm (P95)
Why this matters
Heavy rain is possible on ~1 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Rain Minor
Wet days Measures: Wet days (>=0.1mm). Observed about 34% of days (10.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
10.2 days / month
- Share of days
- ~34% of days
- Upper edge
- Up to ~13mm (P95)
Why this matters
Measurable rain is possible on ~10 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 21% of days (6.2 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
6.2 days / month
- Share of days
- ~21% of days
- Upper edge
- Up to ~99% (P95)
Why this matters
Cloudy skies are possible on ~6 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 20% of days (5.9 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
5.9 days / month
- Share of days
- ~20% of days
- Upper edge
- Up to ~17h (P95)
Why this matters
Several rainy hours are possible on ~6 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Wind Minor
Gusty days Measures: Gusty days (>=40 km/h). Observed about 17% of days (5.0 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
5.0 days / month
- Share of days
- ~17% of days
- Upper edge
- Up to ~58km/h (P95)
Why this matters
Gusty conditions are possible on ~5 days. Exposed activities and transport links are more likely to be disrupted, so keep sheltered alternatives ready.
Rain Minor
Wet most of day Measures: Wet-most-of-day signal (>=6h rain). Observed about 12% of days (3.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
3.6 days / month
- Share of days
- ~12% of days
- Upper edge
- Up to ~20h (P95)
Why this matters
Wet-most-of-day conditions are possible on ~4 days. Outdoor plans can become unreliable, so keep an indoor backup and flexibility around start times.
Cloud Minor
Mostly cloudy days Measures: Mostly cloudy days (cloud cover >=80%). Observed about 9% of days (2.6 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.6 days / month
- Share of days
- ~9% of days
- Upper edge
- Up to ~99% (P95)
Why this matters
Mostly cloudy skies are possible on ~3 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Cold Minor
Cold nights Measures: Cold nights (min <=5C). Observed about 8% of days (2.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
2.5 days / month
- Share of days
- ~8% of days
- Upper edge
- Up to ~5°C (P95)
Why this matters
Cold nights are possible on ~2 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Humidity Minor
High humidity Measures: High humidity days (RH >=80%). Observed about 5% of days (1.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
1.5 days / month
- Share of days
- ~5% of days
- Upper edge
- Up to ~92% (P95)
Why this matters
High humidity is possible on ~2 days. Comfort and pace can drop quickly, so plan shorter outdoor blocks with air-conditioned backup stops.
Cloud Minor
Overcast days Measures: Overcast days (cloud cover >=95%). Observed about 2% of days (0.7 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.7 days / month
- Share of days
- ~2% of days
- Upper edge
- Up to ~100% (P95)
Why this matters
Overcast skies are possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Snow Minor
Snow days Measures: Snow days (>=0.1mm snowfall). Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.5 days / month
- Share of days
- ~2% of days
- Upper edge
- Up to ~9.6mm (P95)
Why this matters
Snowfall is possible on ~1 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Cold Minor
Freezing nights Measures: Freezing nights (min <=0C). Observed about 2% of days (0.5 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.5 days / month
- Share of days
- ~2% of days
- Upper edge
- Up to ~-0°C (P95)
Why this matters
Freezing nights are possible on ~0 days. Fixed-time outdoor plans are safer with a backup option and flexible timing.
Heat Minor
Very hot days Measures: Very hot days (>=35C). Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~37°C (P95)
Why this matters
Very hot days are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Cold Minor
Cold days Measures: Cold days (max <=10C). Observed about 1% of days (0.4 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.4 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~10°C (P95)
Why this matters
Cold daytime conditions are possible on ~0 days. Long outdoor blocks become harder to sustain, so layer up and keep a warm indoor fallback nearby.
Cold Minor
Hard freeze nights Measures: Hard freeze nights (min <=-2C). Observed about 1% of days (0.3 days/month) in September. Historical risk signal only, not a day-by-day forecast.
Likely frequency
0.3 days / month
- Share of days
- ~1% of days
- Upper edge
- Up to ~-2°C (P95)
Why this matters
Hard freeze conditions 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.
Likely frequency
0.1 days / month
- Share of days
- —
- Upper edge
- Up to ~35°C (P95)
Why this matters
Feels-like heatwave runs are possible on ~0 days. Midday activity often needs adjustment around shade, hydration, and indoor fallback options.
Travel planning FAQ
Frequently asked questions
Quick answers to the weather questions you ask the most.
Is September a good time to visit Denver?
Typical September days in Denver reach highs of 25°C (77°F) with nights around 10°C (50°F). It usually feels warm by day and cool after dark. Overall, September sits in the middle of the Denver climate range.
What are temperatures like in September?
In September, you can usually expect highs of 25°C (77°F) and lows near 10°C (50°F). That means warm days and cool nights, so pack layers you can add or remove.
How much does it rain in September?
Rainfall in September averages 34 mm (1.3 in) across roughly 8 days. Overall it is a moderately wet time of year, so showers are usually brief rather than all-day downpours.
How many hours of daylight are there in September?
You can expect about 12 hours of daylight in September. Sunrise is typically around 05:41 and sunset near 18:07. Daylight is fairly typical, with enough time for sightseeing.
How strong is the sun in September?
UV levels are often high (around 7). Regular sunscreen and a hat are recommended.
Is it windy in September?
In September, average wind speeds are around 8 km/h (5 mph), with gusts on the windiest days reaching about 44 km/h (27 mph). On the ground, it is it often feels breezy, especially in more exposed spots or along the coast.