Aurora forecast: when the northern lights show
Is tonight worth going out for the aurora? Eräkaveri combines geomagnetic activity, darkness and cloud cover into an hourly estimate for your own location.
- Hourly forecast for two nights
- The best moment with its date
- Tonight's cloud cover by the hour
- The Kp threshold for your location
What the forecast is made of
Visibility comes down to four things at once: geomagnetic activity, darkness, cloud cover and moonlight. Eräkaveri combines them hour by hour. Activity comes from the NOAA SWPC Kp forecast and the OVATION model, cloud cover from the Finnish Meteorological Institute, and darkness from the sun's altitude at your location.
What the Kp number means where you are
Kp describes geomagnetic disturbance on a 0–9 scale, but the same number means different things in Utsjoki and in Helsinki. In Lapland Kp 1–2 is often enough, around Oulu you typically need Kp 3, and in southern Finland Kp 4 or more. The app derives the threshold from your geomagnetic latitude and states it outright.
Cloud cover decides more often than activity
A bright aurora does not show through cloud. The card therefore shows tonight's cloud cover hour by hour, from the same forecast the fishing and hiking views use. Below 25 per cent is clear, 25–65 partly cloudy.
Season and what the forecast does not promise
The season runs from August to April; in May–July Finland has no real darkness, and the app says so instead of showing a zero. The Kp forecast is most reliable about an hour ahead, so the two-day curve tells you which nights look promising — not that the aurora will certainly appear.
Frequently asked questions
What Kp do the northern lights need in southern Finland?
Usually Kp 4 or more. In Lapland Kp 1–2 is often enough. The app computes the threshold for your location.
Does the forecast work in summer?
In May–July Finland has no real darkness and the app says so. The season starts in August.
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