Last updated: February 24, 2025
In Aspen, United States, September ushers in a harmonious blend of cool and crisp weather, with average temperatures hovering around 9°C (49°F). Daily highs reach a pleasant 24°C (76°F), while nights can dip to a brisk -7°C (19°F). The month experiences 35 mm (1.4 in) of precipitation over 7 days, contributing to a refreshing 65% humidity that blankets the town. This transitional period marks the perfect time for outdoor adventures amidst Aspen’s stunning landscapes, where the changing leaves create a picturesque backdrop.
In September, Aspen experiences a refreshing transition as summer bids farewell, with temperatures that showcase a delightful range. The month greets visitors with a minimum of -7°C (19°F), while the average settles comfortably at 9°C (49°F), peaking at a pleasant 24°C (76°F) during the day. This shift marks a noticeable change from the warm summer months, inviting outdoor enthusiasts to enjoy the vibrant fall foliage against a backdrop of crisp mountain air. As autumn takes hold, the cooler temperatures begin to hint at the approaching winter, yet September remains a charming time for both adventure and relaxation in this picturesque mountain town.
In September, Aspen experiences a transitional weather pattern, with precipitation measuring 35 mm (1.4 in) spread over just 7 days. This marks a continuation of the relatively low rainfall seen in August, where only 37 mm fell. The trend shows a noticeable decline in precipitation as summer ends, countered by the gradual onset of autumn, indicated by a slight increase in moisture levels compared to the drier months of June and July. With the lush summer greenery beginning to recede, September's moderate rainfall serves as a gentle reminder of the shifts in seasons, paving the way for the more substantial precipitation expected in the months ahead.
September in Aspen brings a noticeable shift in humidity as summer dwindles, with levels averaging 65%. This marks a modest increase from the drier midsummer months of July and August, which recorded 52% and 56% respectively. As the crisp fall air starts to settle in, the humidity gently rises, hinting at the transition into autumn. Following the generally drier summer, September’s humidity serves as a reminder of the approaching winter months, where levels climb more substantially, peaking at 89% in December. This gentle oscillation in humidity throughout the year highlights Aspen's unique climate, characterized by refreshing summers and moisture-rich winters.
As summer transitions into fall, the UV Index in Aspen maintains a notably high level in September, reaching 11, which categorizes it as extreme. With a burn time of just 10 minutes, sun safety becomes crucial even as temperatures begin to cool. This month continues the trend set by the summer months, where the UV Index peaked at 15 in June. Compared to the earlier winter months, where UV exposure was moderate to high, September’s intensity underscores the region's persistent sun exposure, making it essential for outdoor enthusiasts to remain vigilant. For more detailed information about UV levels throughout the year, visit Aspen UV Index.
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September in Aspen shines with an impressive 317 hours of sunlight, contributing to the region's transition into autumn. This month experiences a slight dip compared to the sun-soaked summer, where June and July bask in a peak of 386 hours each. However, September maintains a robust brightness, outshining October's 286 hours. As the days begin to shorten, the vibrant fall foliage comes alive under the warm glow of the sun, making it a perfect time for outdoor adventures. The gradual decline from summer heights into early fall offers a captivating blend of warmth and color, inviting visitors to enjoy the breathtaking scenery before winter’s arrival.
In September, Aspen enjoys a notable likelihood of sunny weather, with a 67% chance of sunshine matching the peak levels seen in August. This month transitions from the vibrant summer, characterized by warmer skies, into the cooler fall season, maintaining a high potential for clear, bright days. Notably, the sunny probabilities in September mirror those of August, highlighting a consistent trend toward pleasant weather as summer bids farewell. With the days starting to shorten and autumn colors beginning to emerge, visitors can relish the warm, sunlit afternoons that September generously provides.
As summer transitions into fall, September in Aspen, Colorado, offers 12 hours of daylight, reflecting a gradual decline from the 14 hours enjoyed during the peak summer months. This month serves as a vivid reminder of nature's changing rhythms, with daylight beginning to wane as autumn approaches. Following the increasing daylight from January’s humble 9 hours to June’s zenith, September marks a subtle shift, inviting longer evenings and crisper air. This trend continues into October, where daylight dips to 11 hours, hinting at the cozy, introspective seasons that lie ahead. The slight decrease in sunlight not only alters the landscape but also enhances the beauty of Aspen's fall foliage, making September a captivating time to experience the transition from summer's glow to autumn's embrace.
As summer gives way to fall, September winds in Aspen present a gentle shift, with an average wind speed of 1.9 m/s (4 mph). This subtle decrease in windiness from the summer months, where breezes lingered around 2.0 m/s, marks the onset of cooler temperatures and a tranquil atmosphere. Interestingly, September’s winds are slightly calmer compared to the early spring, showcasing a seasonal transition that invites a serene ambiance. As the year progresses into October, the winds pick up again, suggesting that Aspen's captivating autumn scenery is complemented by a delicate whisper of breezes that enhance the area's natural beauty.
The weather in Aspen 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 Aspen and find detailed weather information for every month.
September and January present strikingly different weather conditions. In September, temperatures range from a chilly -7°C (19°F) at night to a warm max of 24°C (76°F) during the day, with an average temperature of 9°C (49°F). The month experiences approximately 35 mm (1.4 in) of precipitation over about 7 days, accompanied by a moderate humidity level of 65%. In contrast, January is significantly colder, with temperatures dipping as low as -23°C (-10°F) and reaching a maximum of just 5°C (42°F), averaging -9°C (16°F). The winter month sees an increase in precipitation, totaling 59 mm (2.3 in) over 11 days and a higher humidity of 88%. For more insights into January weather specifics, you can check out Aspen weather in January.
September and February present stark contrasts in weather conditions. In September, temperatures range from a chilly minimum of -7°C (19°F) to a warm maximum of 24°C (76°F), with an average of 9°C (49°F). The month experiences relatively low precipitation at 35 mm (1.4 in) over about 7 days and a humidity level of 65%. In contrast, February brings much colder conditions, with temperatures dipping as low as -25°C (-13°F) and averaging -8°C (18°F), peaking at 10°C (50°F). This month sees significantly higher precipitation, totaling 78 mm (3.1 in) across approximately 15 days, alongside increased humidity at 87%. For more detailed insights on February weather specifically, you can explore Aspen weather in February.
In comparing the weather of September and March, September presents a much milder climate with average temperatures around 9°C (49°F), peaking at 24°C (76°F), contrasted with March's chillier average of -4°C (26°F) and a maximum of 11°C (51°F). While September experiences relatively light precipitation at 35 mm (1.4 in) over about 7 days, March sees more substantial rainfall, totaling 82 mm (3.2 in) across 14 days. Additionally, humidity in March is higher at 81%, compared to September's 65%, contributing to a notably different feel in the air during these months. For more insights into March conditions, check out Aspen weather in March.
In September, the weather typically presents a more temperate climate, with average temperatures ranging from a cool 9°C (49°F) to a pleasant 24°C (76°F). This month experiences less precipitation, totaling around 35 mm (1.4 in) over approximately 7 days, accompanied by a moderate humidity level of 65%. In contrast, April is notably chillier, with average temperatures fluctuating between a low of -19°C (-2°F) and a high of 11°C (53°F), leading to a more brisk atmosphere. This month sees higher precipitation levels at 72 mm (2.8 in) over 13 days, and humidity levels rise to 76%. For those interested in a deeper dive into April's climate specifics, you can visit Aspen weather in April.
When comparing the weather in September and May, it is clear that September generally offers milder temperatures, with averages around 9°C (49°F) and a maximum of 24°C (76°F), compared to May's cooler temperatures with an average of 3°C (38°F) and a maximum of 18°C (64°F). September experiences less precipitation, measuring 35 mm (1.4 in) over about 7 days, while May sees higher precipitation at 62 mm (2.4 in) across 12 days. Both months have similar humidity levels, around 65-66%, but the overall feel is warmer in September. For more detailed insights on May weather specifically, check out Aspen weather in May.
In comparing the weather between September and June, both months experience notable variations in temperature and humidity. September tends to have slightly warmer average temperatures, ranging from a minimum of -7°C (19°F) to a maximum of 24°C (76°F), with an overall average of 9°C (49°F). In contrast, June sees similar minimum temperatures but offers a slightly higher average of 10°C (50°F) and a maximum of 25°C (78°F). Precipitation levels are relatively comparable, with September receiving 35 mm (1.4 in) of rain over 7 days, while June has slightly less at 33 mm (1.3 in) over 6 days. Humidity in September is higher at 65%, compared to June’s 58%. For a closer look at June weather specifics, visit Aspen weather in June.
In September, the weather is cooler than in July, with average temperatures ranging from a minimum of -7°C (19°F) to a maximum of 24°C (76°F), compared to July's minimum of -1°C (30°F) and maximum of 26°C (78°F). September experiences slightly less precipitation at 35 mm (1.4 in) over 7 days, while July is wetter with 60 mm (2.4 in) across 12 days. Additionally, September has higher humidity levels at 65%, making it feel more uncomfortable despite the moderate temperatures. For a closer look at summer conditions, check out Aspen weather in July.
Comparing the weather in September and August reveals some notable differences. In September, temperatures range from a minimum of -7°C (19°F) to a maximum of 24°C (76°F), with an average of 9°C (49°F). This contrasts with August, where temperatures are milder, with a minimum of 0°C (33°F), an average of 13°C (55°F), and a maximum of 25°C (77°F). Precipitation in September is slightly lower at 35 mm (1.4 in) over 7 days compared to August's 37 mm (1.5 in) over 8 days. Humidity levels are also higher in September at 65%, compared to 56% in August. For more details about August weather specifically, you can check Aspen weather in August.
In September, the weather offers a more moderate range, with temperatures ranging from a chilly minimum of -7°C (19°F) to a warm maximum of 24°C (76°F), averaging around 9°C (49°F). The month experiences a total precipitation of 35 mm (1.4 in) over about 7 days, accompanied by a humidity level of 65%.
In contrast, October brings a notable dip in temperatures, with minimums plummeting to -30°C (-21°F) and an average of just 1°C (34°F). The maximum temperature is also lower, reaching only 19°C (66°F), while total precipitation rises to 62 mm (2.4 in) spread over 10 days and humidity increases to 76%. For a detailed look at weather specifics during this month, check out Aspen weather in October.
In comparing the weather between September and November, a stark contrast is evident. September boasts a milder climate with average temperatures around 9°C (49°F) and maximums reaching up to 24°C (76°F), while November sees much colder conditions, with average temperatures dropping to -6°C (22°F) and maximums only reaching 11°C (53°F). Additionally, September experiences lower humidity at 65% and less precipitation at 35 mm (1.4 in) across 7 days, whereas November has an increased humidity level of 82% and more precipitation totaling 52 mm (2.1 in) over 9 days. For those interested in more specific details, check out Aspen weather in November.
In September, the weather features a milder temperature range with minimums around -7°C (19°F) and maximums reaching up to 24°C (76°F), averaging 9°C (49°F). The month experiences moderate precipitation of 35 mm (1.4 in) over about seven days, accompanied by a humidity level of 65%. In contrast, December brings a significant drop in temperatures, with minimums plunging to -29°C (-20°F) and a colder average of -9°C (15°F), while maximums only reach 7°C (45°F). December also sees increased precipitation totals of 65 mm (2.6 in) spread over twelve days and higher humidity at 89%. For a detailed look at December weather, you can check Aspen weather in December.
As summer gracefully transitions into autumn, September in Aspen showcases a remarkable shift in weather patterns. With warm days averaging around 9°C and brisk evenings dipping to a nippy -7°C, this month serves as a refreshing interlude before winter settles in. While the air is more humid than the preceding months, the increased precipitation—with about seven days of rain—adds a vibrant twist to the landscape, enhancing the stunning fall foliage. September offers a unique blend of comfortable temperatures and the anticipation of seasonal change, making it an ideal time for outdoor enthusiasts. For a deeper dive into what the climate offers throughout the year, check out Aspen Climate.