Thunder Bay · August 2027
Northern lights in Thunder Bay in August 2027
Answer
August against the rest of the year
August cloud at Thunder Bay averages 64% in NASA POWER's 2001 to 2020 record, 6 points clearer than its yearly mean. No month at Thunder Bay is clearer. By civil night times clear sky, August scores 3.0 hours at Thunder Bay, 7th of 12. Duluth, 278 km away, averages 52%, clearer by 12 points.
Civil night at Thunder Bay starts August at 7 h 38 min and reaches 9 h 22 min by August 31 as the nights lengthen by 1.7 hours. The 10 PM to 2 AM window is fully dark on 23 of 31 nights. True astronomical darkness, the sun 18 degrees down, lasts 5.3 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/Toronto dates. Thunder Bay gets 132 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 27 (4 h), Aug 28 (4 h), Aug 29 (4 h).
- 1
0% lit
7.6 h
- 2
1% lit
7.7 h
- 3
5% lit
7.8 h
- 4
11% lit
7.6 h
- 5
19% lit
7.3 h
- 6
29% lit
7.0 h
- 7
39% lit
6.7 h
- 8
50% lit
6.3 h
- 9
60% lit
5.8 h
- 10
69% lit
5.2 h
- 11
78% lit
4.4 h
- 12
85% lit
3.5 h
- 13
91% lit
2.4 h
- 14
96% lit
1.3 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
93% lit
0.0 h
- 20
87% lit
0.3 h
- 21
79% lit
0.6 h
- 22
70% lit
1.0 h
- 23
60% lit
1.4 h
- 24
49% lit
2.1 h
- 25
38% lit
2.9 h
- 26
28% lit
4.0 h
- 27
18% lit
5.3 h
- 28
10% lit
6.8 h
- 29
4% lit
8.3 h
- 30
1% lit
9.3 h
- 31
0% lit
9.4 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
Thunder Bay needs Kp 5 for the average oval edge to sit overhead. 99 of the 930 August days from 1996 to 2025 (11%) reached it in the GFZ Potsdam record, 5th of 12 months; storm days with Kp 5 or more made up 11%. Thunder Bay sits at 57.1 degrees geomagnetic. By SWPC's rule the average oval edge is overhead at Kp 5, and aurora is usually visible on the northern horizon at G1 (Kp 5) or less.
August across Canada
Thunder Bay ranks 6th in Canada for civil night on August 15, behind Trois-Rivières at 8.7 hours. Coming from July (6.9 hours at Thunder Bay), August adds darkness, and the nights keep growing into September (10.3 hours on the 15th).
| Town | Civil night | Cloud |
|---|---|---|
| Trois-Rivières | 8.7 h | 59% |
| Sydney | 8.7 h | 65% |
| Québec | 8.6 h | 60% |
| Greater Sudbury | 8.6 h | 56% |
| St. John's | 8.5 h | 72% |
| Thunder Bay | 8.4 h | 64% |
| Saguenay | 8.4 h | 68% |
| Winnipeg | 8.3 h | 52% |
| Kelowna | 8.3 h | 45% |
| Lethbridge | 8.3 h | 51% |
| Regina | 8.2 h | 53% |
| Kamloops | 8.2 h | 50% |
Darkness and moon, every night
| Night | Civil | Astronomical | Moon-free dark | Moon-free, 10 PM to 2 AM | Moon lit |
|---|---|---|---|---|---|
| Sun Aug 1 | 7 h 38 min | 4 h 3 min | 7 h 38 min | 3 h 46 min | 0% |
| Mon Aug 2 | 7 h 42 min | 4 h 9 min | 7 h 42 min | 3 h 47 min | 1% |
| Tue Aug 3 | 7 h 45 min | 4 h 14 min | 7 h 45 min | 3 h 49 min | 5% |
| Wed Aug 4 | 7 h 48 min | 4 h 20 min | 7 h 35 min | 3 h 38 min | 11% |
| Thu Aug 5 | 7 h 51 min | 4 h 25 min | 7 h 18 min | 3 h 19 min | 19% |
| Fri Aug 6 | 7 h 55 min | 4 h 31 min | 7 h 1 min | 3 h 1 min | 29% |
| Sat Aug 7 | 7 h 58 min | 4 h 36 min | 6 h 42 min | 2 h 40 min | 39% |
| Sun Aug 8 | 8 h 1 min | 4 h 42 min | 6 h 19 min | 2 h 15 min | 50% |
| Mon Aug 9 | 8 h 5 min | 4 h 47 min | 5 h 49 min | 1 h 44 min | 60% |
| Tue Aug 10 | 8 h 8 min | 4 h 52 min | 5 h 12 min | 1 h 5 min | 69% |
| Wed Aug 11 | 8 h 11 min | 4 h 58 min | 4 h 25 min | 16 min | 78% |
| Thu Aug 12 | 8 h 15 min | 5 h 3 min | 3 h 28 min | 0 min | 85% |
| Fri Aug 13 | 8 h 18 min | 5 h 8 min | 2 h 25 min | 0 min | 91% |
| Sat Aug 14 | 8 h 22 min | 5 h 14 min | 1 h 19 min | 0 min | 96% |
| Sun Aug 15 | 8 h 25 min | 5 h 19 min | 13 min | 0 min | 99% |
| Mon Aug 16 | 8 h 29 min | 5 h 24 min | 0 min | 0 min | 100% |
| Tue Aug 17 | 8 h 32 min | 5 h 29 min | 0 min | 0 min | 99% |
| Wed Aug 18 | 8 h 36 min | 5 h 34 min | 0 min | 0 min | 97% |
| Thu Aug 19 | 8 h 39 min | 5 h 39 min | 0 min | 0 min | 93% |
| Fri Aug 20 | 8 h 43 min | 5 h 44 min | 16 min | 0 min | 87% |
| Sat Aug 21 | 8 h 46 min | 5 h 49 min | 35 min | 13 min | 79% |
| Sun Aug 22 | 8 h 50 min | 5 h 54 min | 58 min | 33 min | 70% |
| Mon Aug 23 | 8 h 54 min | 5 h 59 min | 1 h 27 min | 1 h | 60% |
| Tue Aug 24 | 8 h 57 min | 6 h 4 min | 2 h 4 min | 1 h 35 min | 49% |
| Wed Aug 25 | 9 h 1 min | 6 h 9 min | 2 h 55 min | 2 h 24 min | 38% |
| Thu Aug 26 | 9 h 4 min | 6 h 13 min | 4 h | 3 h 27 min | 28% |
| Fri Aug 27 | 9 h 8 min | 6 h 18 min | 5 h 20 min | 4 h | 18% |
| Sat Aug 28 | 9 h 12 min | 6 h 23 min | 6 h 48 min | 4 h | 10% |
| Sun Aug 29 | 9 h 15 min | 6 h 28 min | 8 h 18 min | 4 h | 4% |
| Mon Aug 30 | 9 h 19 min | 6 h 32 min | 9 h 19 min | 4 h | 1% |
| Tue Aug 31 | 9 h 22 min | 6 h 37 min | 9 h 22 min | 4 h | 0% |
Questions
- Can you see the northern lights in Thunder Bay in August?
- On dark, clear nights with enough activity. 31 of 31 nights at Thunder Bay have civil darkness, and 11% of past August days reached Kp 5.
- How dark is Thunder Bay in August?
- Thunder Bay averages 8.5 hours of civil night a night in August 2027, from 7 h 38 min on the 1st to 9 h 22 min on the last night.
- How cloudy is Thunder Bay in August?
- NASA POWER's 2001 to 2020 climatology gives Thunder Bay's 1 degree cell 64% mean cloud in August, against 70% for the whole year. It is an all-hours average, not a forecast.
- What is the best night in August 2027 for aurora in Thunder Bay?
- By darkness and moon alone, Aug 27, with 4 h of moon-free darkness inside 10 PM to 2 AM at Thunder Bay. Activity on that date will only be known hours ahead.
- Is August or September better in Thunder Bay?
- By civil night times the clear share, August scores 3.0 hours at Thunder Bay and September 3.6. 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.