Nordic Explorer

Aurora tonight in Finland

Six places, each answered from the same four inputs: how disturbed the magnetic field is, how much cloud is forecast over the dark hours, when it actually gets dark, and where the moon is. Every number below says when it was read.

Right now, everywhere

Kp index
3.67 — estimated, one-minute cadence NOAA SWPC,
Forecast tonight
Kp 3.67 from 06:00 Finnish time
Kp 3.67 from 09:00 Finnish time
Kp 2.67 from 12:00 Finnish time
Kp 2.00 from 15:00 Finnish time
Kp 1.67 from 18:00 Finnish time
Kp 1.67 from 21:00 Finnish time
NOAA SWPC three-day forecast, issued
Magnetometers
9 FMI stations reporting, from Hankasalmi to Kevo FMI,

The six places, north to south

How the verdict is worked out

Four inputs, in the order they can rule the night out.

  1. Darkness. Computed here from the date and the coordinates — no feed, so it never fails and never disagrees with the band above it. The aurora needs the sun more than 18° below the horizon. In Lapland that condition does not exist between late May and early August at all, which is why a page can say "too light" in July with total confidence.
  2. Cloud. FMI's HARMONIE model, hourly, at each place's exact coordinates rather than at the nearest town. We take the best hour inside the dark window, because one clear hour is enough and an average is not.
  3. Geomagnetic activity. The NOAA Kp index and the OVATION overhead probability, plus the rate of change of the horizontal magnetic field at the nearest FMI magnetometer. The last of those is the local one, and the one most aurora forecasts leave out.
  4. The moon. Phase, illuminated fraction and altitude at the start of the dark window. A bright moon does not stop the aurora, it removes the faint end of it, so it is a caveat on the verdict rather than part of it.

When a feed does not answer, the page keeps the last reading and its real age, and says how old it is. When there is nothing to keep, the verdict says we could not check — it does not fall back to "clear skies". A page here with no answer is never a green one.

Phase two adds Abisko, Kiruna, Tromsø, Alta, Lofoten and Reykjavík, which need Norwegian and Swedish cloud feeds and their own attribution. Every source, with its licence.