Average Weather in September in Aspen Colorado, United States
Daily high temperatures decrease by 9°F, from 68°F to 59°F, rarely falling below 48°F or exceeding 74°F.
Daily low temperatures decrease by 8°F, from 40°F to 32°F, rarely falling below 25°F or exceeding 47°F.
For reference, on July 8, the hottest day of the year, temperatures in Aspen typically range from 43°F to 73°F, while on January 28, the coldest day of the year, they range from 7°F to 29°F.
Average High and Low Temperature in September
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature in September
The month of September in Aspen experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 32% to 25%. The lowest chance of overcast or mostly cloudy conditions is 25% on September 19.
The clearest day of the month is September 19, with clear, mostly clear, or partly cloudy conditions 75% of the time.
For reference, on February 12, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 51%, while on September 19, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 75%.
Cloud Cover Categories in September
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Aspen, the chance of a wet day over the course of September is gradually decreasing, starting the month at 23% and ending it at 21%.
For reference, the year's highest daily chance of a wet day is 29% on August 1, and its lowest chance is 13% on June 17.
Over the course of September in Aspen, the chance of a day with only rain decreases from 23% to 17%, the chance of a day with mixed snow and rain increases from 0% to 3%, and the chance of a day with only snow remains an essentially constant 1% throughout.
Probability of Precipitation in September
The average sliding 31-day rainfall during September in Aspen is essentially constant, remaining about 1.1 inches throughout, and rarely exceeding 2.3 inches or falling below 0.3 inches.
The highest average 31-day accumulation is 1.2 inches on September 19.
Average Monthly Rainfall in September
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. As with rainfall, we consider the liquid-equivalent snowfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day liquid-equivalent snowfall during September in Aspen is essentially constant, remaining about 0.1 inches throughout, and rarely exceeding 0.4 inches or falling below -0.0 inches.
Average Monthly Liquid-Equivalent Snowfall in September
Over the course of September in Aspen, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 13 minutes, implying an average daily decrease of 2 minutes, 31 seconds, and weekly decrease of 17 minutes, 36 seconds.
The shortest day of the month is September 30, with 11 hours, 49 minutes of daylight and the longest day is September 1, with 13 hours, 2 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in Aspen is 6:35 AM on September 1 and the latest sunrise is 26 minutes later at 7:02 AM on September 30.
The latest sunset is 7:37 PM on September 1 and the earliest sunset is 46 minutes earlier at 6:51 PM on September 30.
Daylight saving time is observed in Aspen during 2018, but it neither starts nor ends during September, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 5:41 AM and sets 14 hours, 56 minutes later, at 8:36 PM, while on December 21, the shortest day of the year, it rises at 7:23 AM and sets 9 hours, 25 minutes later, at 4:47 PM.
Sunrise & Sunset with Twilight in September
The chance that a given day will be muggy in Aspen is essentially constant during September, remaining around 0% throughout.
Humidity Comfort Levels in September
The average hourly wind speed in Aspen is gradually increasing during September, increasing from 4.3 miles per hour to 5.0 miles per hour over the course of the month.
For reference, on April 11, the windiest day of the year, the daily average wind speed is 6.2 miles per hour, while on August 1, the calmest day of the year, the daily average wind speed is 4.0 miles per hour.
Average Wind Speed in September
Wind Direction in September
The growing season in Aspen typically lasts for 2.8 months (86 days), from around June 17 to around September 11, rarely starting before May 28 or after July 9, and rarely ending before August 24 or after September 28.
During September in Aspen, the chance that a given day is within the growing season is very rapidly decreasing falling from 76% to 7% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in September
The average accumulated growing degree days in Aspen are gradually increasing during September, increasing by 130°F, from 879°F to 1,010°F, over the course of the month.
Growing Degree Days in September
The average daily incident shortwave solar energy in Aspen is gradually decreasing during September, falling by 0.9 kWh, from 6.2 kWh to 5.3 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in September
For the purposes of this report, the geographical coordinates of Aspen are 39.191 deg latitude, -106.818 deg longitude, and 8,904 ft elevation.
The topography within 2 miles of Aspen contains large variations in elevation, with a maximum elevation change of 2,808 feet and an average elevation above sea level of 8,629 feet. Within 10 miles contains large variations in elevation (6,437 feet). Within 50 miles also contains extreme variations in elevation (8,950 feet).
The area within 2 miles of Aspen is covered by trees (68%) and shrubs (30%), within 10 miles by trees (73%) and shrubs (13%), and within 50 miles by trees (58%) and shrubs (22%).
This report illustrates the typical weather in Aspen year round, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Aspen.
For each station, the records are corrected for the elevation difference between that station and Aspen according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Aspen is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Aspen and a given station.
The stations contributing to this reconstruction are: Aspen–Pitkin County Airport (54%, 6 kilometers, northwest); Lake County Airport (30%, 43 kilometers, east); and Gunnison County Airport (16%, 74 kilometers, south).
Time zones for aiports and weather stations are provided by AskGeo.com .