Tromsdalen · September 2027
Northern lights in Tromsdalen in September 2027
Answer
September against the rest of the year
September cloud at Tromsdalen averages 82% in NASA POWER's 2001 to 2020 record, close to its yearly mean of 82%. July is Tromsdalen's clearest month at 79%. By civil night times clear sky, September scores 1.5 hours at Tromsdalen, 7th of 12. Tromsø, 2 km away, averages the same 82%.
Civil night at Tromsdalen starts September at 5 h 57 min and reaches 10 h 35 min by September 30 as the nights lengthen by 4.6 hours. SWPC's 10 PM to 2 AM window is fully dark on every night. The sun never reaches 18 degrees down, so Tromsdalen gets no astronomical night in September.
September night by night
Full moon comes first, on Sep 16, then the new moon on Sep 30, in Europe/Oslo dates. Tromsdalen gets 128 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: Sep 1 (4 h), Sep 2 (4 h), Sep 3 (4 h).
- 1
2% lit
6.0 h
- 2
7% lit
6.2 h
- 3
14% lit
6.3 h
- 4
22% lit
6.5 h
- 5
32% lit
6.7 h
- 6
42% lit
6.9 h
- 7
52% lit
7.0 h
- 8
61% lit
7.2 h
- 9
70% lit
7.4 h
- 10
79% lit
7.5 h
- 11
86% lit
7.7 h
- 12
92% lit
3.3 h
- 13
96% lit
1.4 h
- 14
99% lit
0.0 h
- 15
100% lit
0.0 h
- 16
99% lit
0.0 h
- 17
96% lit
0.0 h
- 18
91% lit
0.0 h
- 19
85% lit
0.0 h
- 20
76% lit
0.0 h
- 21
67% lit
0.0 h
- 22
56% lit
0.0 h
- 23
45% lit
0.0 h
- 24
33% lit
0.0 h
- 25
23% lit
2.5 h
- 26
14% lit
5.7 h
- 27
7% lit
8.1 h
- 28
2% lit
10.3 h
- 29
0% lit
10.4 h
- 30
1% lit
10.6 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 Septembers
Quiet activity already puts the oval edge over Tromsdalen, so storm days matter more: 126 of the 900 September days from 1996 to 2025 (14%) reached Kp 5, one of the three most active months for that level. Tromsdalen sits at 67.5 degrees geomagnetic, inside SWPC's 60 to 75 degree band, where aurora can be seen on more than half of all nights. No storm is needed: by SWPC's rule the average oval edge is overhead at Kp 0.
September across Norway
Tromsdalen ranks 19th in Norway for civil night on September 15, behind Kristiansand at 9.8 hours. Coming from August (0.6 hours at Tromsdalen), September adds darkness, and the nights keep growing into October (12.7 hours on the 15th). The September equinox falls on September 23, 07:56 Tromsdalen time, inside the weeks SWPC links with larger storms.
| Town | Civil night | Cloud |
|---|---|---|
| Kristiansand | 9.8 h | 74% |
| Stavanger | 9.7 h | 79% |
| Haugesund | 9.7 h | 78% |
| Oslo | 9.6 h | 73% |
| Bergen | 9.6 h | 79% |
| Drammen | 9.6 h | 73% |
| Hamar | 9.5 h | 70% |
| Lillehammer | 9.5 h | 74% |
| Gjøvik | 9.5 h | 70% |
| Ålesund | 9.4 h | 82% |
| Molde | 9.4 h | 82% |
| Trondheim | 9.3 h | 78% |
| Tromsdalen | 8.4 h | 82% |
Darkness and moon, every night
| Night | Civil | Astronomical | Moon-free dark | Moon-free, 10 PM to 2 AM | Moon lit |
|---|---|---|---|---|---|
| Wed Sep 1 | 5 h 57 min | 0 min | 5 h 57 min | 4 h | 2% |
| Thu Sep 2 | 6 h 9 min | 0 min | 6 h 9 min | 4 h | 7% |
| Fri Sep 3 | 6 h 20 min | 0 min | 6 h 20 min | 4 h | 14% |
| Sat Sep 4 | 6 h 31 min | 0 min | 6 h 31 min | 4 h | 22% |
| Sun Sep 5 | 6 h 42 min | 0 min | 6 h 42 min | 4 h | 32% |
| Mon Sep 6 | 6 h 52 min | 0 min | 6 h 52 min | 4 h | 42% |
| Tue Sep 7 | 7 h 3 min | 0 min | 7 h 3 min | 4 h | 52% |
| Wed Sep 8 | 7 h 13 min | 0 min | 7 h 13 min | 4 h | 61% |
| Thu Sep 9 | 7 h 23 min | 0 min | 7 h 23 min | 4 h | 70% |
| Fri Sep 10 | 7 h 33 min | 0 min | 7 h 33 min | 4 h | 79% |
| Sat Sep 11 | 7 h 43 min | 0 min | 7 h 43 min | 4 h | 86% |
| Sun Sep 12 | 7 h 53 min | 0 min | 3 h 20 min | 43 min | 92% |
| Mon Sep 13 | 8 h 3 min | 0 min | 1 h 23 min | 0 min | 96% |
| Tue Sep 14 | 8 h 12 min | 0 min | 0 min | 0 min | 99% |
| Wed Sep 15 | 8 h 22 min | 0 min | 0 min | 0 min | 100% |
| Thu Sep 16 | 8 h 31 min | 0 min | 0 min | 0 min | 99% |
| Fri Sep 17 | 8 h 40 min | 0 min | 0 min | 0 min | 96% |
| Sat Sep 18 | 8 h 49 min | 1 h 2 min | 0 min | 0 min | 91% |
| Sun Sep 19 | 8 h 59 min | 1 h 48 min | 0 min | 0 min | 85% |
| Mon Sep 20 | 9 h 8 min | 2 h 20 min | 0 min | 0 min | 76% |
| Tue Sep 21 | 9 h 17 min | 2 h 45 min | 0 min | 0 min | 67% |
| Wed Sep 22 | 9 h 26 min | 3 h 8 min | 0 min | 0 min | 56% |
| Thu Sep 23 | 9 h 34 min | 3 h 28 min | 0 min | 0 min | 45% |
| Fri Sep 24 | 9 h 43 min | 3 h 46 min | 0 min | 0 min | 33% |
| Sat Sep 25 | 9 h 52 min | 4 h 3 min | 2 h 30 min | 15 min | 23% |
| Sun Sep 26 | 10 h 1 min | 4 h 19 min | 5 h 41 min | 3 h 17 min | 14% |
| Mon Sep 27 | 10 h 9 min | 4 h 34 min | 8 h 8 min | 4 h | 7% |
| Tue Sep 28 | 10 h 18 min | 4 h 49 min | 10 h 18 min | 4 h | 2% |
| Wed Sep 29 | 10 h 26 min | 5 h 2 min | 10 h 26 min | 4 h | 0% |
| Thu Sep 30 | 10 h 35 min | 5 h 16 min | 10 h 35 min | 4 h | 1% |
Questions
- Can you see the northern lights in Tromsdalen in September?
- On dark, clear nights with enough activity. 30 of 30 nights at Tromsdalen have civil darkness, and 14% of past September days reached Kp 5.
- How dark is Tromsdalen in September?
- Tromsdalen averages 8.4 hours of civil night a night in September 2027, from 5 h 57 min on the 1st to 10 h 35 min on the last night.
- How cloudy is Tromsdalen in September?
- NASA POWER's 2001 to 2020 climatology gives Tromsdalen's 1 degree cell 82% mean cloud in September, against 82% for the whole year. It is an all-hours average, not a forecast.
- What is the best night in September 2027 for aurora in Tromsdalen?
- By darkness and moon alone, Sep 1, with 4 h of moon-free darkness inside 10 PM to 2 AM at Tromsdalen. Activity on that date will only be known hours ahead.
- Is September or October better in Tromsdalen?
- By civil night times the clear share, September scores 1.5 hours at Tromsdalen and October 2.2. October 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.