How do our guides decide where to go each night? We combine live space-weather data — KP index, Bz orientation, solar wind speed and proton density — with real-time cloud cover across a 200 km radius, then add years of local knowledge of Ruka's microclimates. All of that data is on our public aurora monitor.
Here's a look under the hood at how we read a night.
The data we watch
- KP index (0–9): overall geomagnetic activity. At Ruka's 66°N, aurora shows from KP 1
- Bz (IMF orientation): the direction of the Sun's magnetic field — arguably as important as KP
- Solar wind speed: 500+ km/s is promising
- Proton/plasma density: how much material is arriving
- Cloud cover: hour-by-hour, across a wide radius
Why Bz matters as much as KP
Here's the piece most guides don't explain: the KP number tells you activity, but Bz tells you whether Earth's 'door' is open. When Bz points south (negative), solar particles couple efficiently into our magnetic field and the aurora lights up — even at a modest KP. A high KP with a northward Bz can underdeliver, while a moderate KP with a strongly southward Bz can put on a show. We watch Bz constantly.
Reading Ruka's microclimates
Data gets you close; local knowledge closes the deal. We know which valleys trap cloud, which lakeshores and fell tops clear first, and how a front will move across Kuusamo. That's why we can often find a clear window when the forecast looks marginal.
Turning data into a decision
Each evening we check the monitor, weigh KP and Bz against the cloud maps, and choose a direction — sometimes a nearby lakeside, sometimes a 100 km drive to the only clear sky within range. Then we adapt in real time as conditions shift.
See the data yourself
You don't have to take our word for it — the same live feeds are on our aurora monitor, and our guides put them to work on every Aurora Hunting Tour.