Climate averages 1991–2020
Rapid City weather
in August.
A hot, moderately wet month: the 2nd warmest and the 8th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
August is a hot month in Rapid City: daytime highs average 28.2°C and nights cool to about 16.1°C. By daytime temperature it is the 2nd warmest of the 12 months.
Expect about 60 mm of rain on roughly 11 days, which makes August a moderately wet month (the 8th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 14 h 01 min on an average August day.
The nearest other city in this atlas is Bismarck (358 km away). In August its highs average 26.9°C, 1.3°C cooler than Rapid City, with 58 mm of rain.
Among the 498 cities listed in the United States, Rapid City ranks joint 313th of 498 for the warmest August highs and 216th of 498 for the driest August (rainfall, lowest first). The mean August high of those 498 cities is 29.9°C; Rapid City is 1.7°C cooler than that mean.
From August to September, average highs fall by 4.9°C to 23.3°C, and monthly rainfall falls from 60 mm to 42 mm.
The annual picture
August in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Rapid City climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 2.5°C-8.1°C | -8.1°C | 13 | 3.9 | 9.39 h |
| February | 3.5°C-7.6°C | -7.6°C | 20 | 5.1 | 10.410 h |
| March | 8.5°C-3.5°C | -3.5°C | 40 | 7.6 | 11.912 h |
| April | 12.8°C1.1°C | 1.1°C | 80 | 11.8 | 13.413 h |
| May | 18.4°C7.2°C | 7.2°C | 112 | 14.1 | 14.715 h |
| June | 24.4°C12.9°C | 12.9°C | 97 | 14.5 | 15.415 h |
| July | 28.9°C16.9°C | 16.9°C | 78 | 13.4 | 15.115 h |
| August, selected | 28.2°C16.1°C | 16.1°C | 60 | 10.8 | 14.014 h |
| September | 23.3°C11.2°C | 11.2°C | 42 | 6.7 | 12.613 h |
| October | 14.9°C3.9°C | 3.9°C | 50 | 7.3 | 11.011 h |
| November | 7.9°C-2.5°C | -2.5°C | 20 | 4.4 | 9.710 h |
| December | 2.8°C-6.9°C | -6.9°C | 15 | 3.6 | 9.09 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
August in nearby cities
- Bismarck in AugustUnited States · 358 kmHigh 26.9°C · Low 15.9°C · 58 mm rain
- Fort Collins in AugustUnited States · 417 kmHigh 28.2°C · Low 14.0°C · 37 mm rain
- Greeley in AugustUnited States · 424 kmHigh 30.5°C · Low 16.0°C · 31 mm rain
- Loveland in AugustUnited States · 437 kmHigh 28.2°C · Low 14.0°C · 37 mm rain
- Billings in AugustUnited States · 456 kmHigh 30.0°C · Low 15.8°C · 18 mm rain
- Longmont in AugustUnited States · 462 kmHigh 28.3°C · Low 14.3°C · 39 mm rain
- Boulder in AugustUnited States · 482 kmHigh 27.5°C · Low 13.7°C · 71 mm rain
- Thornton in AugustUnited States · 490 kmHigh 28.0°C · Low 13.8°C · 39 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Rapid City) is explained once on the Rapid City year overview and on the Sources, method and limits page.