What do Kp numbers mean?
The Kp number is a system of measuring aurora strength. It goes from 0 to 9 (0 being very weak, 9 being a major geomagnetic storm with strong auroras visible).
So when your looking at the aurora forecast page, you want to see high Kp numbers. The higher the better. Anything above (and including) Kp5 is classed as a geomagnetic storm.
Did you know?
The abbreviation Kp comes from the German "Planetarische Kennziffer". Although it is better known in English as the planetary index.