Rapid City · August 2027
Northern lights in Rapid City in August 2027
Answer
August against the rest of the year
August cloud at Rapid City averages 42% in NASA POWER's 2001 to 2020 record, 15 points clearer than its yearly mean. July is Rapid City's clearest month at 42%. By civil night times clear sky, August scores 5.2 hours at Rapid City, 4th of 12. Fargo, 590 km away, averages 49%, cloudier by 7 points.
Civil night at Rapid City starts August at 8 h 13 min and reaches 9 h 40 min by August 31 as the nights lengthen by 1.4 hours. SWPC's 10 PM to 2 AM window is fully dark on every night. True astronomical darkness, the sun 18 degrees down, lasts 6.2 hours on the 15th.
August night by night
August opens toward a new moon on Aug 2 and Aug 31, with full moon on Aug 17, in America/Denver dates. Rapid City gets 139 hours of civil night with the moon below the horizon across the month. The best of them for moon-free darkness inside 10 PM to 2 AM: Aug 1 (4 h), Aug 2 (4 h), Aug 3 (4 h).
- 1
0% lit
8.2 h
- 2
1% lit
8.3 h
- 3
5% lit
8.2 h
- 4
12% lit
7.8 h
- 5
20% lit
7.5 h
- 6
30% lit
7.1 h
- 7
40% lit
6.7 h
- 8
51% lit
6.3 h
- 9
61% lit
5.7 h
- 10
70% lit
5.0 h
- 11
79% lit
4.2 h
- 12
86% lit
3.3 h
- 13
92% lit
2.3 h
- 14
96% lit
1.2 h
- 15
99% lit
0.2 h
- 16
100% lit
0.0 h
- 17
99% lit
0.0 h
- 18
97% lit
0.0 h
- 19
92% lit
0.2 h
- 20
86% lit
0.6 h
- 21
78% lit
0.9 h
- 22
69% lit
1.4 h
- 23
59% lit
1.9 h
- 24
49% lit
2.6 h
- 25
38% lit
3.5 h
- 26
27% lit
4.6 h
- 27
17% lit
5.9 h
- 28
9% lit
7.3 h
- 29
3% lit
8.7 h
- 30
0% lit
9.6 h
- 31
0% lit
9.7 h
Each cell is the night that starts on that date. Hours are civil-dark time with the moon below the horizon; the green rule scales with them. Green outline: new moon. Bone outline: full moon.
Activity in past Augusts
Rapid City needs Kp 8 for the average oval edge to sit overhead. 3 of the 930 August days from 1996 to 2025 (0%) reached it in the GFZ Potsdam record, 7th of 12 months; storm days with Kp 5 or more made up 11%. Rapid City sits at 51.8 degrees geomagnetic. The lowest NOAA storm level whose typical viewing latitude reaches it is G3 (Kp = 7). By SWPC's rule the average oval edge is overhead only at Kp 8.
August across United States
Rapid City ranks 2nd in United States for civil night on August 15, behind Buffalo at 9.0 hours. Coming from July (7.6 hours at Rapid City), August adds darkness, and the nights keep growing into September (10.5 hours on the 15th).
| Town | Civil night | Cloud |
|---|---|---|
| Buffalo | 9.0 h | 56% |
| Rapid City | 8.9 h | 42% |
| Portland, Maine | 8.9 h | 52% |
| Minneapolis | 8.8 h | 49% |
| Duluth | 8.6 h | 52% |
| Fargo | 8.6 h | 49% |
| Seattle | 8.5 h | 48% |
| Juneau | 6.9 h | 79% |
| Anchorage | 6.3 h | 79% |
| Eagle River | 6.2 h | 79% |
| Fairbanks | 5.0 h | 75% |
Darkness and moon, every night
| Night | Civil | Astronomical | Moon-free dark | Moon-free, 10 PM to 2 AM | Moon lit |
|---|---|---|---|---|---|
| Sun Aug 1 | 8 h 13 min | 5 h 14 min | 8 h 13 min | 4 h | 0% |
| Mon Aug 2 | 8 h 15 min | 5 h 18 min | 8 h 15 min | 4 h | 1% |
| Tue Aug 3 | 8 h 18 min | 5 h 22 min | 8 h 13 min | 4 h | 5% |
| Wed Aug 4 | 8 h 21 min | 5 h 26 min | 7 h 51 min | 4 h | 12% |
| Thu Aug 5 | 8 h 23 min | 5 h 30 min | 7 h 30 min | 4 h | 20% |
| Fri Aug 6 | 8 h 26 min | 5 h 34 min | 7 h 8 min | 3 h 56 min | 30% |
| Sat Aug 7 | 8 h 29 min | 5 h 38 min | 6 h 44 min | 3 h 31 min | 40% |
| Sun Aug 8 | 8 h 32 min | 5 h 42 min | 6 h 16 min | 3 h 2 min | 51% |
| Mon Aug 9 | 8 h 34 min | 5 h 46 min | 5 h 43 min | 2 h 27 min | 61% |
| Tue Aug 10 | 8 h 37 min | 5 h 50 min | 5 h 2 min | 1 h 45 min | 70% |
| Wed Aug 11 | 8 h 40 min | 5 h 54 min | 4 h 13 min | 55 min | 79% |
| Thu Aug 12 | 8 h 43 min | 5 h 58 min | 3 h 18 min | 0 min | 86% |
| Fri Aug 13 | 8 h 46 min | 6 h 2 min | 2 h 17 min | 0 min | 92% |
| Sat Aug 14 | 8 h 49 min | 6 h 6 min | 1 h 14 min | 0 min | 96% |
| Sun Aug 15 | 8 h 52 min | 6 h 10 min | 11 min | 0 min | 99% |
| Mon Aug 16 | 8 h 55 min | 6 h 14 min | 0 min | 0 min | 100% |
| Tue Aug 17 | 8 h 58 min | 6 h 18 min | 0 min | 0 min | 99% |
| Wed Aug 18 | 9 h | 6 h 22 min | 0 min | 0 min | 97% |
| Thu Aug 19 | 9 h 3 min | 6 h 26 min | 13 min | 0 min | 92% |
| Fri Aug 20 | 9 h 6 min | 6 h 29 min | 34 min | 0 min | 86% |
| Sat Aug 21 | 9 h 9 min | 6 h 33 min | 57 min | 0 min | 78% |
| Sun Aug 22 | 9 h 12 min | 6 h 37 min | 1 h 23 min | 0 min | 69% |
| Mon Aug 23 | 9 h 15 min | 6 h 41 min | 1 h 56 min | 14 min | 59% |
| Tue Aug 24 | 9 h 19 min | 6 h 45 min | 2 h 37 min | 53 min | 49% |
| Wed Aug 25 | 9 h 22 min | 6 h 49 min | 3 h 29 min | 1 h 44 min | 38% |
| Thu Aug 26 | 9 h 25 min | 6 h 53 min | 4 h 35 min | 2 h 48 min | 27% |
| Fri Aug 27 | 9 h 28 min | 6 h 57 min | 5 h 52 min | 4 h | 17% |
| Sat Aug 28 | 9 h 31 min | 7 h | 7 h 16 min | 4 h | 9% |
| Sun Aug 29 | 9 h 34 min | 7 h 4 min | 8 h 41 min | 4 h | 3% |
| Mon Aug 30 | 9 h 37 min | 7 h 8 min | 9 h 37 min | 4 h | 0% |
| Tue Aug 31 | 9 h 40 min | 7 h 12 min | 9 h 40 min | 4 h | 0% |
Questions
- Can you see the northern lights in Rapid City in August?
- On dark, clear nights with enough activity. 31 of 31 nights at Rapid City have civil darkness, and 0% of past August days reached Kp 8.
- How dark is Rapid City in August?
- Rapid City averages 8.9 hours of civil night a night in August 2027, from 8 h 13 min on the 1st to 9 h 40 min on the last night.
- How cloudy is Rapid City in August?
- NASA POWER's 2001 to 2020 climatology gives Rapid City's 1 degree cell 42% mean cloud in August, against 57% for the whole year. It is an all-hours average, not a forecast.
- What is the best night in August 2027 for aurora in Rapid City?
- By darkness and moon alone, Aug 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Rapid City. Activity on that date will only be known hours ahead.
- Is August or September better in Rapid City?
- By civil night times the clear share, August scores 5.2 hours at Rapid City and September 5.9. September comes out ahead.
Sources and verification
- SunCalchttps://github.com/mourner/suncalc
- NASA POWER climatologyhttps://power.larc.nasa.gov/docs/services/api/temporal/climatology/
- GFZ Potsdam Kp indexhttps://kp.gfz.de/en/data
- NOAA SWPC, Tips on viewing the aurorahttps://www.spaceweather.gov/content/tips-viewing-aurora
Quoted figures last checked against their sources on 2026-09-30; next review 2026-12-31. Computed figures come from SunCalc and the IGRF-14 dipole as described in the methodology. Every quote is listed in the sources ledger.