Boulder, CO weather in September
In September, Boulder sees highs around 79°F and lows around 48°F: mild, with some rain. Expect about 8 wet days. Snowfall averages about 1.0 in. Good for outdoor plans.
- Normal high
- 79°F
- Normal low
- 48°F
- Wet days
- 8
- 2.1 in total
- Snowfall
- 1.0 in
- normal snowfall
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 84°F | 73°F |
| Normal low | 53°F | 43°F |
| Chance of a wet day | 28% | 24% |
| Sunrise / sunset | 6:28 am / 7:33 pm | 6:56 am / 6:45 pm |
| Daylight | 13.1 h | 11.8 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Mountain Time).
A typical September day
- 6 am53°Fdew point 40°F
- 9 am65°Fdew point 40°F
- Noon74°Fdew point 37°F
- 3 pm77°Fdew point 36°F
- 6 pm69°Fdew point 38°F
- 9 pm60°Fdew point 40°F
NOAA hourly normals (local standard time) from Denver Intl Airport (35 mi away); average wind 9 mph; clear or few clouds in 46% of daytime hours, mostly cloudy or overcast in 35%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F13 of 30
- Hot dayshigh 90°F or more3 of 30
- Muggy daysdaily mean dew point 65°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow8 of 30
- Notable rainat least 0.10 in4 of 30
- Freezing nightslow 32°F or below1 of 30
- Snow on the groundsnow depth 1 in or more0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain and snow in September
Normal precipitation is 2.1 in; a dry September brings about 0.6 in and a wet one about 2.5 in (25th and 75th percentiles). About 1 day brings half an inch or more. Normal snowfall is 1.0 in.
How September varies from year to year
- Warmest September, 1991-20202019: average high 85°F
- Coolest September2006: average high 73°F
- Wettest September2013: 18.2 in
- Driest September1992: 0.02 in
- Highest reading100°F (September 2, 2019)
- Lowest reading23°F (September 22, 1995)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 86°F | 79°F | 66°F |
| Normal low | 56°F | 48°F | 37°F |
| Wet days | 11 | 8 | 7 |
| Comfortable days | 5 | 13 | 16 |
| Daylight | 13.7 h | 12.4 h | 11.1 h |
Highs change by -7°F from August and -13°F into October.
Nearby alternatives in September
- Warmer: Moab, UT250 mi · high 88°F · 5 wet days
- Drier: Pueblo, CO127 mi · high 83°F · 5 wet days
- Cooler: Estes Park, CO28 mi · high 70°F · 9 wet days
How Boulder ranks in September
- Normal high212th warmest of 378 cities; 6th of 17 in Colorado
- Wet days190th driest of 378
- Comfortable days120th most of 342
What to pack for Boulder in September
- Layers – afternoons near 79°F but nights near 48°F
Heating and cooling
September has 112 heating degree days and 65 cooling degree days (base 65°F), 3% of the year's total heating and cooling demand.
Questions
How hot is Boulder in September?
The normal high is 79°F and the normal low is 48°F. From 1991 to 2020 the hottest September reading was 100°F (September 2, 2019).
Does it rain a lot in Boulder in September?
About 8 days in September have at least 0.01 in of precipitation, and the normal total is 2.1 in. The wettest September in 1991-2020 was in 2013 (18.2 in); the driest was in 1992 (0.02 in).
Does it snow in Boulder in September?
Yes. Normal snowfall in September is 1.0 in.
Is September a good time to visit Boulder?
September ranks 4th of 12 months on our comfort score for Boulder (66 out of 100). It has about 13 comfortable days and about 3 days at 90°F or hotter. The best month is May.
Where the numbers come from
- Temperature, rain, snowfall, snow depth and frost dates: Boulder (USC00050848), 1.6 mi S of the city center, 5,484 ft (165 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Humidity and wind by hour: Denver Intl Airport (USW00003017), 35 mi ESE of the city center, 5,414 ft (95 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Cloud cover: Aurora Buckley Fld ANGB (USW00023036), 35 mi SE of the city center, 5,663 ft (344 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Denver International Airport (725650-03017), 35 mi ESE of the city center, 5,404 ft (85 ft higher than the city). Hourly observations, 1991-2020.