September weather forecast
Aspen, CO

The icy Maroon Bells in the Elk Mountains viewed from the White River below
The icy Maroon Bells in the Elk Mountains viewed from the White River below

Weather in September

The first month of the autumn, September, is also an enjoyable month in Aspen, Colorado, with average temperature varying between 34.5°F (1.4°C) and 61°F (16.1°C).

Temperature

In Aspen, the average high-temperature slightly decreases, from a comfortable 67.3°F (19.6°C) in August, to a still enjoyable 61°F (16.1°C). The average low-temperature, in Aspen, is 34.5°F (1.4°C).

Humidity

The average relative humidity in September is 59%.

Rainfall

September is the month with the least rainfall. Rain falls for 5.5 days and accumulates 0.2" (5mm) of precipitation.

Snowfall

Months with snowfall are January through June, September through December. September is the first month it typically snows in Aspen. Throughout September, in the average 1.1 snowfall days, it receives 0.08" (2mm) of snow. In Aspen, Colorado, during the entire year, snow falls for 83.2 days, and aggregates up to 19.45" (494mm) of snow.

Daylight

The average length of the day in September is 12.4h.

Sunshine

The average sunshine is 10.9h.

UV index

In September, the average daily maximum UV index in Aspen is 3. A UV Index reading of 3 to 5 represents a moderate threat to health from unsafe exposure to the UV radiation for the ordinary person.
Note: In September, the average maximum UV index of 3 translate into the following recommendations:
Take precautions - Protection against sun damage is advised. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes. Beware! The strength of the UV rays is increased nearly double-fold by the reflection of the snow.
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FAQ

What is the average humidity in September in Aspen?

The average relative humidity in September in Aspen is 59%.

What is the driest month in Aspen?

September is the month with the least rainfall in Aspen, Colorado. Rain falls for 5.5 days and accumulates 0.2" (5mm) of precipitation.

How many days does it rain in September in Aspen?

In September, the rain falls for 5.5 days. Throughout September, 0.2" (5mm) of precipitation is accumulated.

When does it start snowing in Aspen?

September is the first month it typically snows in Aspen, Colorado. Throughout September, in the average 1.1 snowfall days, it receives 0.08" (2mm) of snow.

How many hours of daylight does Aspen have in September?

In Aspen, the average length of the day in September is 12.4h.

How long on average sun shines in September in Aspen?

The average sunshine in September is 10.9h.

How high is the UV index in September in Aspen?

In Aspen, the average daily maximum UV index in September is 3. A UV Index estimate of 3 to 5 represents a moderate vulnerability from the exposure to the Sun's UV radiation.

Average temperature in September
Aspen, CO

Average temperature in September - Aspen, CO
  • Average high temperature in September: 61°F

The warmest month (with the highest average high temperature) is July (69.4°F).
Months with the lowest average high temperature are January and December (24.4°F).

  • Average low temperature in September: 34.5°F

The month with the highest average low temperature is July (40.5°F).
The coldest month (with the lowest average low temperature) is January (2.1°F).

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Average pressure in September
Aspen, CO

Average pressure in September - Aspen, CO
  • Average pressure in September: 30.06"

The month with the highest atmospheric pressure is January (30.23").
Months with the lowest atmospheric pressure are April and May (29.95").

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Average wind speed in September
Aspen, CO

Average wind speed in September - Aspen, CO
  • Average wind speed in September: 4.8mph

The windiest month (with the highest average wind speed) is June (6.2mph).
The calmest months (with the lowest average wind speed) are January and August (4.5mph).

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Average humidity in September
Aspen, CO

Average humidity in September - Aspen, CO
  • Average humidity in September: 59%

The month with the highest relative humidity is February (90%).
The month with the lowest relative humidity is June (51%).

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Average rainfall in September
Aspen, CO

Average rainfall in September - Aspen, CO
  • Average rainfall in September: 0.2"

The wettest months (with the highest rainfall) are March and July (0.51").
The driest month (with the least rainfall) is September (0.2").

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Average rainfall days in September
Aspen, CO

Average rainfall days in September - Aspen, CO
  • Average rainfall days in September: 5.5 days

The month with the highest number of rainy days is July (12.1 days).
The month with the least rainy days is January (2.8 days).

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Average snowfall in September
Aspen, CO

Average snowfall in September - Aspen, CO
  • Average snowfall in September: 0.08"

The month with the highest snowfall is March (3.98").
Months with the least snowfall are July and August (0").

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Average snowfall days in September
Aspen, CO

Average snowfall days in September - Aspen, CO
  • Average snowfall days in September: 1.1 days

The month with the highest number of snowfall days is February (12.8 days).
Months with the least snowfall days are July and August (0.1 days).

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Average daylight in September /
Average sunshine in September
Aspen, CO

Average daylight in September / Average sunshine in September - Aspen, CO
  • Average daylight in September: 12.4h

The month with the longest days is June (Average daylight: 14.9h).
The month with the shortest days is December (Average daylight: 9.5h).

  • Average sunshine in September: 10.9h

The month with the most sunshine is June (Average sunshine: 11.8h).
The month with the least sunshine is February (Average sunshine: 5.2h).

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Average sunshine days in September
Aspen, CO

Average sunshine days in September - Aspen, CO
  • Average sunshine days in September: 17.8 days

The month with the most sunshine days is November (23.6 days).
The month with the least sunshine days is July (9.8 days).

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Average UV index in September
Aspen, CO

Average UV index in September - Aspen, CO
  • Average UV index in September: 3

Months with the highest UV index are June, July and August (UV index 4).
Months with the lowest UV index are February and December (UV index 1).

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Average cloud cover in September
Aspen, CO

Average cloud cover in September - Aspen, CO
  • Average cloud cover in September: 17

The month with the most cloud cover is February (Cloud cover 53).
The month with the least cloud cover is June (Cloud cover 15).

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Average visibility in September
Aspen, CO

Average visibility in September - Aspen, CO
  • Average visibility in September: 6mi

Months with the highest visibility are May, June, July, August, September and October (6mi).
Months with the lowest visibility are January, February, March and December (4mi).

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