September 21 is generally a great time to visit Denver. While there is a slight chance of rain (18%), showers are usually brief. Expect comfortable 24°C weather. As it's peak season for Denver, we recommend booking your stay well in advance to secure the best rates.
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Essential Travel Info for Denver
Currency
USD
$ United States dollar
Language
English
Driving
Right side
Safety
Moderate Safety
GPI: 2.44
Denver Weather Forecast for September 21
"Mild & Comfortable. Expect average highs of 24.4°C. 18% chance of snow."
What to Wear in Denver in September
Based on historical data for September 21, Denver typically experiences temperatures between 9.1°C and 24.4°C. We recommend packing light jacket, long pants, layers (onion system) to stay comfortable. Trends suggest it will stay mostly dry (18% rain probability), but checking the forecast before heading out is always wise.
Complete Packing Guide
Weekly breakdown & essential items for Denver
Smart Suitcase
- Light Jacket
- Long Pants
- Layers (Onion System)
Average High
24.4°C
Daytime Peak
Average Low
9.1°C
Nighttime Low
Feels Like
24.6°C
☀️ Feels accurate
Snow Chance
18%
Avg 1mm if it snows
Snowfall
0.1 cm
~18% chance
Pressure
1013.3 hPa
Medium volatility
Denver Weather Conditions & UV Index
Weather Confidence
30-year variance analysis
Based on 10 years of data
🎯 This date historically delivers consistent weather 84% of the time. Safe to plan outdoor activities with confidence.
Sun Exposure
UV Index & Safety Guide
Protection Needed
SPF 30 recommended
05:00 - 10:00
16:00 - 18:00
Type I-II
🔴 21 min to burn
Type III-IV
🟡 32 min to burn
Type V-VI
🟢 53 min to burn
UV estimate based on latitude, season & cloud cover. Actual UV may vary.
Outdoor Comfort
How pleasant is it outside?
Dew Point
13°C
Pleasant
Heat Stress
Low
No heat warning
😊 Best outdoor time:
Any time during daylight hours
Travel & Logistics Insights
Local Calendar
Business Day
Standard hours in United States
Flight Traffic
High
96/100 pressure index
Health Advisory
Healthy
Routine only • View Details →
Landing Slots
~1,109
Daily arrival options (inc. codeshare)
Sunrise, Sunset & Wind in Denver
Daylight & Sun
Solar Elevation Cycle
🌅 Sunrise
05:47
☀️ Noon
11:54
🌇 Sunset
18:00
⏱️ Daylight
12h 13m
Wind Speed
14.8 km/h
Gentle breeze
Sunshine
9.8 hrs
Direct Sun (Cloud-free)
Humidity
49%
Comfortable
Travel Intelligence
Exclusive flight analytics & health data for Denver
Smart Flight Estimator
Airport-to-Airport Logistics
unlock smart flight estimates
Add your home location in settings to see airport details.
Travel Health & Safety in Denver
Travel Comfort Index
Real-time tourism conditions
Weather Quality
☀️ Excellent
Tourist Crowds
🟡 Busy
Price Level
💰💰💰 Expensive
Health & Wellbeing
Meteo-Health Forecast
Moderate fluctuations. Some sensitivity possible.
Weather unlikely to affect joint pain.
Moderate fish activity expected.
Air quality is excellent. Perfect for outdoor activities.
Regional Safety Profile
Seismic Activity
Zero seismic activity detected in 30 years.
"According to 30YearWeather's analysis of 30 years of NASA satellite data, Denver on September 21 averages 24.4°C with a 18% precipitation probability. Wedding/Outdoor Event Score: 98/100."
— Source: 30YearWeather.com|Data: NASA POWER (1991-2021)|View Methodology
Denver Weather History (2010–2024)
Temperature History
Hall of Fame
Records from last 10 years
Better Alternatives Nearby
Consider these dates within ±7 days
September 14
26°C • 16% rain
Score
100
September 15
26°C • 15% rain
Score
100
September 16
26°C • 12% rain
Score
100
💡 Moving your event by a few days could significantly improve weather conditions
Compare Other Cities
Same date (September 21) in other destinations
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Czech Republic
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Rome
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United Kingdom
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Netherlands
🌍 Explore the same date in different destinations around the world
📍 Is Denver Worth Visiting on September 21?
Planning a trip to Denver on September 21? Our historical weather analysis based on 30 years of NASA satellite data shows that this time of year is characterized by pleasant mild weather averaging 24.4°C with a 18% historical precipitation risk.
✈️ Travel Logistics: Approximately 1,109 landing slots available daily during this period, indicating peak tourist activity.
📊 Historical Extremes: The hottest September 21 recorded in the last 30 years saw temperatures hit 30.9°C in 2017, while the coldest dropped to 7.2°C in 2021.