Climate averages 1991–2020
Rapid City weather
by month.
See how the year changes. July has the highest average daily maximum; January has the lowest average monthly rainfall.
Pleasant-weather months by our simple rule: September
Long-term climate patterns, not a forecast for a particular trip.
Across the year Rapid City averages a daytime high of 14.7°C and a nighttime low of 3.4°C, with about 628 mm of rain on roughly 103 days. July is the warmest month (average high 28.9°C) and January the coolest (2.5°C). May is the wettest month with 112 mm; January is the driest with 13 mm.
Months with pleasant weather by a simple rule (average high between 18°C and 29°C, average low of at least 5°C and at most 8 rain days): September. This looks at temperature and rain only, not humidity, wind, sea temperature or crowds.
The annual picture
A year in Rapid City
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 | 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
Nearby cities
- BismarckUnited States · 358 kmHigh 11.4°C · Low 1.4°C · 541 mm precipitation a year
- Fort CollinsUnited States · 417 kmHigh 16.0°C · Low 2.2°C · 479 mm rain a year
- GreeleyUnited States · 424 kmHigh 17.9°C · Low 3.8°C · 358 mm rain a year
- LovelandUnited States · 437 kmHigh 16.1°C · Low 2.0°C · 479 mm rain a year
- BillingsUnited States · 456 kmHigh 15.1°C · Low 3.0°C · 417 mm rain a year
- LongmontUnited States · 462 kmHigh 16.2°C · Low 2.4°C · 495 mm rain a year
- BoulderUnited States · 482 kmHigh 15.6°C · Low 1.8°C · 660 mm rain a year
- ThorntonUnited States · 490 kmHigh 16.0°C · Low 1.5°C · 504 mm rain a year
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 limitsWhat do the high and low temperatures mean?
We average the daily maximum and daily minimum for each calendar month over 1991–2020. They are not record extremes, a forecast range or temperatures at a fixed time of day.
How is a rain day counted?
A local calendar day (standard time, UTC-7, no daylight saving) with at least 1 mm of total precipitation counts as one rain day. We count these for each year and month, then average across 30 years. The average does not predict which days will be wet.
Where do the numbers come from?
ERA5-Land (temperature) and ERA5 (precipitation) reanalysis from the Copernicus Climate Change Service, read from the Open-Meteo open-data archive. Temperature comes from the 0.1° model cell at 44.10°, -103.20° (3 km from the city centre), adjusted up by 0.3°C for the difference between the city's elevation (990 m) and the cell's (1,031 m). Rain comes from the 0.25° cell at 44.00°, -103.25°. These are model estimates, not weather-station readings; coast, hills and city streets can differ.
Does this page show sunshine, humidity or sea temperature?
No. The data used here contain air temperature and precipitation only. Daylight hours are calculated from the city's latitude (sunrise to sunset), not measured sunshine.