Rapid City, SD weather in September
Expect mild weather with some rain in Rapid City in September, with highs near 76°F and lows near 46°F. Rain falls on about 7 days. Good for outdoor plans.
- Normal high
- 76°F
- Normal low
- 46°F
- Wet days
- 7
- 1.2 in total
- Muggy days
- 0
- dew point 65°F+
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 82°F | 69°F |
| Normal low | 52°F | 41°F |
| Chance of a wet day | 22% | 23% |
| Sunrise / sunset | 6:16 am / 7:29 pm | 6:49 am / 6:36 pm |
| Daylight | 13.2 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 42°F
- 9 am64°Fdew point 44°F
- Noon71°Fdew point 43°F
- 3 pm74°Fdew point 42°F
- 6 pm67°Fdew point 43°F
- 9 pm59°Fdew point 43°F
NOAA hourly normals (local standard time) from Ellsworth AFB (8 mi away); average wind 10 mph; clear or few clouds in 58% of daytime hours, mostly cloudy or overcast in 31%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F12 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 snow7 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 0.8 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 0.1 in.
How September varies from year to year
- Warmest September, 1991-20201998: average high 82°F
- Coolest September1993: average high 70°F
- Wettest September2014: 3.2 in
- Driest September2012: 0.1 in
- Highest reading104°F (September 5, 2020)
- Lowest reading19°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 | 85°F | 76°F | 60°F |
| Normal low | 56°F | 46°F | 34°F |
| Wet days | 8 | 7 | 7 |
| Comfortable days | 6 | 12 | 10 |
| Daylight | 14.0 h | 12.5 h | 11.0 h |
Highs change by -9°F from August and -16°F into October.
Nearby alternatives in September
- Cooler: Keystone, SD16 mi · high 69°F · 7 wet days
How Rapid City ranks in September
- Normal high257th warmest of 378 cities; 1st of 4 in South Dakota
- Wet days135th driest of 378
- Comfortable days132nd most of 342
What to pack for Rapid City in September
- Layers – afternoons near 76°F but nights near 46°F
Heating and cooling
September has 175 heating degree days and 62 cooling degree days (base 65°F), 3% of the year's total heating and cooling demand.
Questions
How hot is Rapid City in September?
The normal high is 76°F and the normal low is 46°F. From 1991 to 2020 the hottest September reading was 104°F (September 5, 2020).
Does it rain a lot in Rapid City in September?
About 7 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 2014 (3.2 in); the driest was in 2012 (0.1 in).
Does it snow in Rapid City in September?
Yes. Normal snowfall in September is 0.1 in.
Is September a good time to visit Rapid City?
September ranks 3rd of 12 months on our comfort score for Rapid City (65 out of 100). It has about 12 comfortable days and about 4 days at 90°F or hotter. The best months are May and June.
Where the numbers come from
- Temperature and rain: Rapid City Rgnl Airport (USW00024090), 9.2 mi ESE of the city center, 3,160 ft (83 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Snowfall, snow depth and frost dates: Rapid City WFO (USC00396948), 1.1 mi ESE of the city center, 3,379 ft (136 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Humidity and wind by hour and cloud cover: Ellsworth AFB (USW00024006), 8.1 mi NE of the city center, 3,215 ft . NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Rapid City Regional Airport (726620-24090), 9.1 mi ESE of the city center, 3,162 ft (81 ft lower than the city). Hourly observations, 1991-2020.