Cloud Cover
What we always begin looking at is the cloud cover. That’s because even if we have an amazing display of northern lights, it’s no good if the clouds are blocking it. I mostly use the the website Auroraforecast.is and the Icelandic Meteorological Office to check the cloud cover. You can scroll for the forecasted cloud cover hour by hour. On Auroraforecast.is no colour is no cloud cover, low clouds are blue, middle clouds are red and high clouds are green. We want of course no clouds in the area where we are staying.
KP Aurora Forecast (Common Misconception)
On the same website you can see a so called Kp-index Forecast which is often mistaken as an indicator on how strong the Northern Lights will be. The KP-index is however is more about what latitude the lights will be visible at. KP1 for example would be very low on the horizon while KP4-5 would be overhead. Often when the KP is 6 or more then we don’t see them in Iceland because they are too far south.
In Iceland KP 2-4 is often perfect.
Solar Windspeed & Interplanetary Magnetic Field
The solar wind is what carries the electrons that create the Northern Lights toward earth so the higher the number for solar wind the better. Everything over 500 is really good. Below the wind speed you can also see a number for the density, the higher the number for density the better. If the density goes over 8 protons/cm3 then that can compensate for low solar wind speed.
The Interplanetary Magnetic Field is also a very important thing, we need the needle to be on the negative (minus) side. If we have good solar wind and negative IMF then we are in for a treat. But even if we just have average solar wind if the IMF is very negative that can make up for it.
Magnetic Observatory
The magnetic observatory is not something that predicts the Northern Lights but is more like a real time measurement device. So if you are comfy in your hotel room and you see the H line jumping up and down like in the example then there is a good possibility that something is going on outside (given that there are no clouds blocking the view).