Thornton, CO weather in September
Thornton is warm and mostly dry in September: highs average 80°F and nights drop to about 48°F. There are about 6 days with rain or snow. Snowfall averages about 0.8 in. A good month for most outdoor plans.
- Normal high
- 80°F
- Normal low
- 48°F
- Wet days
- 6
- 1.2 in total
- Snowfall
- 0.8 in
- normal snowfall
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 85°F | 74°F |
| Normal low | 53°F | 42°F |
| Chance of a wet day | 20% | 19% |
| Sunrise / sunset | 6:27 am / 7:31 pm | 6:55 am / 6:44 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 am52°Fdew point 40°F
- 9 am65°Fdew point 40°F
- Noon74°Fdew point 36°F
- 3 pm76°Fdew point 35°F
- 6 pm68°Fdew point 39°F
- 9 pm60°Fdew point 41°F
NOAA hourly normals (local standard time) from Aurora Buckley Fld ANGB (16 mi away); average wind 8 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°F11 of 30
- Hot dayshigh 90°F or more4 of 30
- Muggy daysdaily mean dew point 65°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow6 of 30
- Notable rainat least 0.10 in3 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 1.2 in; a dry September brings about 0.5 in and a wet one about 1.5 in (25th and 75th percentiles). About 1 day brings half an inch or more. Normal snowfall is 0.8 in.
How September varies from year to year
- Warmest September, 1991-20202019: average high 85°F
- Coolest September2006: average high 72°F
- Wettest September2013: 6.4 in
- Driest September1992: no measurable precipitation
- Highest reading99°F (September 6, 2020)
- Lowest reading27°F (September 29, 1999)
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 | 88°F | 80°F | 67°F |
| Normal low | 57°F | 48°F | 36°F |
| Wet days | 8 | 6 | 5 |
| Comfortable days | 5 | 11 | 14 |
| Daylight | 13.7 h | 12.4 h | 11.1 h |
Highs change by -8°F from August and -13°F into October.
Nearby alternatives in September
- Cooler: Estes Park, CO46 mi · high 70°F · 9 wet days
How Thornton ranks in September
- Normal high196th warmest of 378 cities; 4th of 17 in Colorado
- Wet days98th driest of 378
- Comfortable days147th most of 342
What to pack for Thornton in September
- Layers – afternoons near 80°F but nights near 48°F
Heating and cooling
September has 108 heating degree days and 83 cooling degree days (base 65°F), 3% of the year's total heating and cooling demand.
Questions
How hot is Thornton in September?
The normal high is 80°F and the normal low is 48°F. From 1991 to 2020 the hottest September reading was 99°F (September 6, 2020).
Does it rain a lot in Thornton in September?
About 6 days in September have at least 0.01 in of precipitation, and the normal total is 1.2 in. The wettest September in 1991-2020 was in 2013 (6.4 in); the driest was in 1992, with no measurable precipitation.
Does it snow in Thornton in September?
Yes. Normal snowfall in September is 0.8 in.
Is September a good time to visit Thornton?
September ranks 5th of 12 months on our comfort score for Thornton (63 out of 100). It has about 11 comfortable days and about 4 days at 90°F or hotter. The best month is May.
Where the numbers come from
- Temperature, snowfall and snow depth: Denver-Stapleton (USW00023062), 9.1 mi SE of the city center, 5,286 ft (61 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Rain and frost dates: Northglenn (USC00055984), 3.1 mi NW of the city center, 5,407 ft (60 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Humidity and wind by hour and cloud cover: Aurora Buckley Fld ANGB (USW00023036), 16 mi SE of the city center, 5,663 ft (316 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Denver International Airport (725650-03017), 17 mi E of the city center, 5,404 ft (57 ft higher than the city). Hourly observations, 1991-2020.