Guide
What is the Kp index?
The Kp index is the number every aurora forecast revolves around. It's a simple 0–9 scale of global geomagnetic activity — and the higher it climbs, the further from the poles the aurora becomes visible.
What the number means
When the solar wind disturbs Earth's magnetic field, the auroral oval — the ring of aurora around each magnetic pole — grows and pushes toward the equator. The Kp index measures that disturbance every three hours on a scale of 0 (very quiet) to 9 (extreme storm). NOAA also maps the storm levels onto a G-scale (G1 minor through G5 extreme).
The Kp you need depends on your latitude
This is the key idea: a given Kp shows the aurora at a particular geomagnetic latitude — which isn't the same as your map latitude. The further you are from the auroral oval, the higher the Kp you need.
| Kp | Level | Roughly visible from |
|---|---|---|
| 0–2 | Quiet | Directly under the oval (Tromsø, Fairbanks, Yellowknife) |
| 3–4 | Unsettled / Active | Northern Scandinavia, central Canada, southern Iceland |
| 5 | G1 Minor storm | Scotland, southern Canada, northern US states |
| 6–7 | G2–G3 storm | Northern England, Germany, much of the northern US |
| 8–9 | G4–G5 storm | Far south — England, central US, even further on rare nights |
Want the exact figure for a place? Every city forecast page shows the Kp that city needs — for example Edinburgh or Seattle.
Why Kp alone isn't enough
Common Kp questions
Is Kp 5 good?
Kp 5 is a G1 minor storm — enough for the aurora to reach Scotland, southern Canada and the northern US states. Under the oval it's a strong night; in central Europe it usually isn't enough.
How accurate is the 3-day forecast?
It's good for the trend, not the hour — storm arrival times can slip by half a day and strength is often revised. Treat it as a heads-up, then check the live forecast on the night itself.
Do I need Kp 9 in central Europe?
Not quite — from northern Germany a camera can catch the glow around Kp 6–7, and Kp 8 can bring it into naked-eye range. Nights like that are rare, though: a handful per solar cycle.
Plan the trip
Tours, stays and wheels
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