# Dark hours and clear skies, by base and month

Canonical: https://northernlightsindex.com/northern-lights-tours/best-month-by-base/

Two numbers per base per month, and both of them ours. How many hours the sun spends more than twelve degrees below the horizon, and how often an observer at that base's own weather station actually saw a clear sky in those hours.

Six bases: Tromsø, Rovaniemi, Reykjavík, Kiruna, Yellowknife and Fairbanks. One weather station each, every one of them inside 10 km of the base, named on every row.

Dark hours come from solar position and need no licence. The clear-sky share is observed sky cover from NOAA's Integrated Surface Database, a US government work in the public domain.

A month with fewer than 200 dark-hour observations gets its dark-hours figure and no cloud share, rather than a share computed from a handful of hours. That is why the summer rows are part blank at the northern bases.

A chase needs two things from the sky before anything else can go right: it has to be dark, and it has to be clear. Both vary by base and by month in ways that no booking page will tell you, and both can be worked out without anyone's permission.

Dark hours are arithmetic. The sun's position is computed from the date and the station's coordinates, and the figure is the mean number of hours per day with the sun below minus twelve degrees, the point at which the sky is dark enough for a faint aurora to read against it. The clear-sky share is observed: of the hourly observations that fall inside those dark hours, the share where the observer at that station recorded two eighths of cloud or less. Ten years, 2015 to 2024.

What this is not is a forecast, and it is not a probability of seeing the aurora. Darkness and a clear sky are necessary for a sighting. Solar activity, which this page says nothing about, decides whether there is anything to see once you have them.

## Destinations

- [Tromsø](https://northernlightsindex.com/northern-lights-tours/tromso/): 25 tours · from $81
- [Rovaniemi](https://northernlightsindex.com/northern-lights-tours/rovaniemi/): 49 tours · from $88
- [Reykjavík](https://northernlightsindex.com/northern-lights-tours/reykjavik/)

Source: noaa-isd-pds.s3.amazonaws.com. 72 rows, checked 2026-10-28.

Dark hours are computed from solar position at the station's coordinates. The clear-sky share is observed sky cover in those hours, 2015 to 2024, from the station named on the row.

| Base | Month | Dark hours a day | Clear sky | Half clear or better | Observations | Station | km from base | Read from | Checked |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Fairbanks | January | 14.36 | 59.1 | 82.9 | 2377 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | February | 11.91 | 58.5 | 78.2 | 1810 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | March | 8.87 | 55.9 | 78.7 | 1437 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | April | 4.24 | 55.5 | 83.9 | 553 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | May | 0 |  |  | 0 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | June | 0 |  |  | 0 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | July | 0 |  |  | 0 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | August | 0 |  |  | 94 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | September | 6.96 | 34.1 | 60.7 | 891 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | October | 10.57 | 41.4 | 66.8 | 1522 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | November | 13.45 | 45.9 | 67.3 | 1635 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Fairbanks | December | 14.98 | 53.5 | 74.3 | 2181 | FAIRBANKS INTERNATIONAL | 8.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | January | 14.85 | 92.7 | 92.7 | 931 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | February | 11.99 | 96.3 | 96.3 | 729 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | March | 8.46 | 95.6 | 95.6 | 751 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | April | 1.94 |  |  | 182 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | May | 0 |  |  | 0 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | June | 0 |  |  | 0 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | July | 0 |  |  | 0 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | August | 0 |  |  | 39 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | September | 6.13 | 96.7 | 96.7 | 427 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | October | 10.44 | 93.5 | 93.5 | 781 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | November | 13.78 | 92.5 | 92.5 | 929 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Kiruna | December | 15.59 | 88.7 | 88.7 | 849 | KIRUNA | 0.4 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | January | 14.26 | 15.7 | 25.7 | 1224 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | February | 11.89 | 12.2 | 20.8 | 1116 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | March | 8.95 | 16.3 | 26.5 | 838 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | April | 4.55 | 12.9 | 24 | 404 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | May | 0 |  |  | 0 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | June | 0 |  |  | 0 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | July | 0 |  |  | 0 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | August | 0 |  |  | 194 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | September | 7.11 | 15.6 | 26.4 | 621 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | October | 10.59 | 13.5 | 22.5 | 1156 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | November | 13.38 | 14.2 | 27.1 | 1140 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Reykjavík | December | 14.86 | 15.3 | 27.5 | 1373 | REYKJAVIK | 0 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | January | 14.63 | 32 | 34 | 1337 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | February | 11.96 | 23.4 | 25.1 | 952 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | March | 8.65 | 35.7 | 38.3 | 652 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | April | 3.17 |  |  | 119 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | May | 0 |  |  | 0 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | June | 0 |  |  | 0 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | July | 0 |  |  | 0 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | August | 0 |  |  | 44 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | September | 6.51 | 17.6 | 18.4 | 414 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | October | 10.5 | 18.5 | 20.7 | 855 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | November | 13.64 | 22.1 | 23.2 | 1411 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Rovaniemi | December | 15.32 | 32.5 | 35.2 | 1223 | ROVANIEMI | 0.6 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | January | 15.22 | 35 | 40.2 | 3338 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | February | 12.05 | 29 | 34.2 | 2501 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | March | 8.14 | 27.4 | 32.4 | 1688 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | April | 0 | 26.7 | 32.7 | 202 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | May | 0 |  |  | 0 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | June | 0 |  |  | 0 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | July | 0 |  |  | 0 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | August | 0 |  |  | 3 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | September | 5.43 | 32.3 | 36.7 | 1050 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | October | 10.34 | 30.1 | 34.5 | 2420 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | November | 14.03 | 29.4 | 34.4 | 3024 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Tromsø | December | 16.06 | 26.1 | 31.8 | 3430 | TROMSO | 0.3 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | January | 14.04 | 59.9 | 72.7 | 2439 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | February | 11.84 | 67.4 | 78.8 | 2223 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | March | 9.12 | 70.2 | 81.6 | 1896 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | April | 5.21 | 65.5 | 83.4 | 1036 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | May | 0 |  |  | 13 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | June | 0 |  |  | 0 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | July | 0 |  |  | 0 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | August | 2.35 | 50.2 | 71.1 | 478 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | September | 7.44 | 59.4 | 77.3 | 1328 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | October | 10.64 | 37 | 48.8 | 1752 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | November | 13.23 | 34 | 46.4 | 1742 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |
| Yellowknife | December | 14.6 | 50.4 | 65.3 | 2284 | YELLOWKNIFE | 3.9 | https://noaa-isd-pds.s3.amazonaws.com/isd-history.csv | 2026-10-28 |

## Why minus twelve degrees and not sunset?

Because the sky is still too bright at sunset. Minus twelve is inside nautical twilight, roughly the point where a faint aurora reads against the background. It is a threshold we chose; the figure is recomputed if we change it, and the choice is stated here rather than buried.

## Is the clear-sky share a chance of seeing the northern lights?

No, and we are careful not to present it as one. It is how often the sky over that station was clear during dark hours, averaged over ten years. Whether the aurora is active on your night is a separate question this site does not answer.

## Which base comes out best?

It depends on the month, which is the point of the table. Sort by clear-sky share within a month and the inland and continental bases tend to beat the coastal ones; sort by dark hours and the far northern bases win in midwinter and lose in the shoulder season.

## Can I reuse these figures?

Yes, with attribution and a link to the methodology page. The cloud figures derive from public-domain NOAA observations, and the licence at the foot of the methodology page covers our own rows.

## Related

- [Aurora tours that promise a second night: every policy we could read](https://northernlightsindex.com/northern-lights-tours/retry-and-guarantee-policies/)

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