The Kp Index and the Northern Lights: What Kp You Need, and Where

The Kp index measures how disturbed the Earth’s magnetic field is, from 0 to 9, every three hours; the higher it goes, the further from the poles the aurora reaches. NOAA’s rule of thumb puts the oval’s edge near 66° geomagnetic latitude at Kp 0, moving about 2° towards the equator per Kp step. So close to the oval, in Tromsø, Alta, Lofoten, Abisko, Yellowknife and Fairbanks, a quiet night of Kp 0 to 1 is often enough, and Reykjavik needs about Kp 1.0: cloud is the real forecast. That is why the tour to book there is one that drives to the clear sky and covers a cloudy night, such as Northern Lights Bus’s small-group tour from Reykjavik, from US$113 as of October 2026, with a free retry.

Check dates for the Reykjavik tour →

What Kp you need at each destination

Corrected geomagnetic latitude (IGRF-13, 2020.5) of each site’s nearest observatory, published by ISGI, adjusted for the distance to the site; Kp needed from NOAA’s rule of thumb. Estimates, checked October 2026.

And further south

No northern lights tours on GetYourGuide leave from these cities (October 2026); they see the aurora only on strong nights. Corrected geomagnetic latitude from the nearest observatory (ISGI): Dombås for Oslo, Nurmijärvi for Helsinki, Eskdalemuir for Edinburgh, Victoria for Seattle, Brandon for Minneapolis.

How often is Kp 3 or more?

In the GFZ Kp record for 2015 to 2025, the share of dark three-hour windows at Kp 3 or more was highest around the equinoxes: across the European destinations, 30% in September and 29% in March, against 18% in January. Each destination page charts its own month by month. For the year-by-year picture, see is 2026 a good year.

Where to read the forecast

NOAA’s Space Weather Prediction Center publishes a free three-day Kp forecast, and the GFZ publishes the measured index. Every destination page on this site reads NOAA’s Kp forecast and MET Norway’s cloud forecast live, in the “tonight” strip at the top.

The forecast is free, so why a tour?

Because under the oval the Kp forecast rarely decides the night; the cloud does, and it changes by the hour. A guide reads both every evening, picks the direction and drives to the gap, and on the Reykjavik bus tours you get a free retry if the sky stays shut.