September 18 is generally a great time to visit Aspen. While there is a slight chance of rain (20%), showers are usually brief. Expect comfortable 20°C weather. It's a lively time to explore Aspen, with most attractions operating at full capacity.
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Essential Travel Info for Aspen
Currency
USD
$ United States dollar
Language
English
Driving
Right side
Safety
Moderate Safety
GPI: 2.44
Aspen Weather Forecast for September 18
"Mild & Comfortable. Expect average highs of 19.7°C. 20% chance of snow."
What to Wear in Aspen in September
Based on historical data for September 18, Aspen typically experiences temperatures between 4.3°C and 19.7°C. We recommend packing light jacket, long pants, layers (onion system) to stay comfortable. Trends suggest it will stay mostly dry (20% rain probability), but checking the forecast before heading out is always wise.
Complete Packing Guide
Weekly breakdown & essential items for Aspen
Smart Suitcase
- Light Jacket
- Long Pants
- Layers (Onion System)
Average High
19.7°C
Daytime Peak
Average Low
4.3°C
Nighttime Low
Feels Like
19.7°C
🌤️ Feels accurate
Snow Chance
20%
Avg 0.9mm if it snows
Snowfall
0.2 cm
~20% chance
Pressure
1017.4 hPa
Low volatility
Aspen Weather Conditions & UV Index
Weather Confidence
30-year variance analysis
Based on 10 years of data
🎯 This date historically delivers consistent weather 99% 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
🔴 18 min to burn
Type III-IV
🟡 27 min to burn
Type V-VI
🟢 45 min to burn
UV estimate based on latitude, season & cloud cover. Actual UV may vary.
Outdoor Comfort
How pleasant is it outside?
Dew Point
10.9°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
Busy
60/100 pressure index
Health Advisory
Healthy
Routine only • View Details →
Landing Slots
~50
Daily arrival options (inc. codeshare)
Sunrise, Sunset & Wind in Aspen
Daylight & Sun
Solar Elevation Cycle
🌅 Sunrise
05:52
☀️ Noon
12:02
🌇 Sunset
18:13
⏱️ Daylight
12h 20m
Wind Speed
12.5 km/h
Gentle breeze
Sunshine
11.0 hrs
Direct Sun (Cloud-free)
Humidity
57%
Comfortable
Travel Intelligence
Exclusive flight analytics & health data for Aspen
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 Aspen
Travel Comfort Index
Real-time tourism conditions
Weather Quality
☀️ Excellent
Tourist Crowds
🟡 Busy
Price Level
💰💰💰 Expensive
Health & Wellbeing
Meteo-Health Forecast
Stable conditions. Low risk of headaches.
Weather unlikely to affect joint pain.
Moderate fish activity expected.
Air quality is excellent. Perfect for outdoor activities.
Regional Safety Profile
Seismic Activity
Rare minor tremors. Buildings are earthquake-resistant.
"According to 30YearWeather's analysis of 30 years of NASA satellite data, Aspen on September 18 averages 19.7°C with a 20% precipitation probability. Wedding/Outdoor Event Score: 89/100."
— Source: 30YearWeather.com|Data: NASA POWER (1991-2021)|View Methodology
Aspen Weather History (2010–2024)
Temperature History
Hall of Fame
Records from last 10 years
Better Alternatives Nearby
Consider these dates within ±7 days
September 25
18.7°C • 14% rain
Score
92
September 11
20.8°C • 21% rain
Score
91
September 12
20.5°C • 23% rain
Score
91
💡 Moving your event by a few days could significantly improve weather conditions
Compare Other Cities
Same date (September 18) in other destinations
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📍 Is Aspen Worth Visiting on September 18?
Planning a trip to Aspen on September 18? 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 19.7°C with a 20% historical precipitation risk.
✈️ Travel Logistics: Approximately 50 landing slots available daily during this period, indicating manageable crowd levels.
📊 Historical Extremes: The hottest September 18 recorded in the last 30 years saw temperatures hit 25.8°C in 2018, while the coldest dropped to -0.3°C in 2025.