Your chance of seeing the aurora depends on where you are, the month and above all how many nights you stay, because cloud decides most nights.
Key takeaways
- The odds come from counting real runs of consecutive nights in weather and aurora records, so cloudy spells lasting several nights are already included.
- Faint, proper display and strong show mean Kp 1, Kp 2 and Kp 3 or more during a clear hour.
- The calculator's answer is usually lower than the simple formula, and it flags the gap under the result when the gap is big.
- The figures behind the calculator are free to download as a CSV and reuse, with credit to Northern Lights Planner.
On this page
Work out your odds
Loading the calculator. If it doesn't appear, the same figures are in the tables on how many nights you need.
How to read the result
In short The big number is your chance of at least one clear evening hour with the aurora active at your chosen level, and the bars show how it grows each night.
- The big number is the chance of at least one good night during your stay: at least one hour in the evening window with a clear sky while the aurora was active at your chosen level.
- Faint, proper display, strong show are the three levels used across the site: Kp 1, Kp 2 and Kp 3 or more during a clear hour. How the odds are worked out explains them.
- The bars show how the chance grows with each extra night. Tap a bar to jump to that number of nights.
- Copy link to this result gives you a link to exactly what you're looking at, to share or come back to.
Why the real odds are lower than the simple sum
In short Bad nights come in runs because a storm system can sit over a place for several nights, so real odds fall below the independent-nights formula.
The simple way to work out your chances is to take the odds of one good night and assume every night is independent. Weather doesn't work like that: a storm system can sit over a place for several nights, so bad nights come in runs. This calculator counts what actually happened in every real run of nights in the records, which is why its answer is usually lower than the formula's. Where the gap is big, the calculator says so under the result.
What it can't tell you
- It is based on one weather station per place; hills and coast nearby can be clearer or cloudier.
- Airport cloud sensors miss thin high cloud, so the clear-sky figures are, if anything, slightly generous.
- Abisko has 7 winters of records, so its figures are less certain than Fairbanks' 26.
- It is not a forecast. For tonight, use the NOAA or University of Alaska Fairbanks forecasts.
Use the data
- The figures behind the calculator are free to reuse, with credit to Northern Lights Planner: download the table as CSV.
- Each row is one place, month, level and number of nights, with the chance from real runs and from the simple formula side by side.
Odds calculator: common questions
Where does the calculator get its numbers?
From hourly weather reports at Fairbanks, Reykjavík and Keflavík airports and the Abisko weather station, joined to the GFZ Kp index of geomagnetic activity, night by night. The methodology page lists every source and the years covered.
Why doesn't it include Tromsø, Rovaniemi or Yellowknife?
We only include places where we have measured night-by-night records with the same method. Those three aren't measured that way yet, so they aren't in the calculator.
Is this a forecast for my dates?
No. It shows how often a stay of that length in that month would have included a good night in past years. For the next few days, use an aurora forecast.