The short answer ...
The Aurora happens in space, every day of the year. September to March is the right time to visit Tromsø for a chance to witness this spectacle because, during this time, the sky is dark at night. There is no particular period of the year during which the Aurora is predictably stronger than average or is more likely to be seen. We recommend avoiding full-moon nights. How many nights you stay in Tromsø and how many chases you join has the biggest impact on your chances.
The complete answer ...
Many factors determine how your chances are from night to night, but one concept remains true under any circumstances:
The more often you chase the Northern Lights, the higher your chances to see them.
Based on this concept it is advisable to spend more than just one or two nights in Tromsø. Most of our guests stay between three and six nights. We recommend that you sign up for several chases on your first nights in town. Read more on this here:
Northern Lights can only be seen if the sky is dark enough. In Tromsø first sightings are usually reported at the end of August, however, at this time there's only an hour or two of darkness every night. Your chances are highest from mid-September.
In mid-March, the winter comes to an end and the sky becomes bright during the early evening hours. We still see the Northern Lights on most nights in March, but in April your chances will be seriously affected. It is practically impossible to see the Northern Lights later than mid-April.
Northern Norway is well known for its harsh and unpredictable weather. There isn't one particular time of the season during which weather conditions are generally better, therefore, choosing the "right month" is not an option. Every day of the season has the potential for a clear or overcast sky. Keep in mind that if the weather in Tromsø is not in our favour we will head inland where we often find clear conditions.
As beautiful as the moon is, its reflection causes our sky to light up brightly at night. This can affect your viewing experience and even your chances to see the Aurora. For example, during a bright full-moon night even a strong Northern Lights display may be harder to see, a weak display that may already be difficult to spot even on a moonless night may not be seen at all.
A bit of moonlight can also enhance your experience as the landscape appears brightly lit, revealing the beautiful scenery of mountains and the sea around us. Especially photographers find this appealing.
Our general recommendation is therefore to avoid nights surrounding the full moon period. If you happen to only be able to travel during the full moon, do not worry too much. We've seen some of our favourite displays on those brightly lit nights.
"Aurora forecast" apps attempt to predict your chances of seeing the Northern Lights by using the kp-index measurement. The efficacy of this is questionable, however, since we only require a kp-index of 0 for a chances to see the Northern Lights.
Solar Cycle / 27-day forecast
On average, the sun rotates around its axis once every 27 days. A sunspot that has caused spectacular Auroras by facing Earth may therefore be in the same favourable position 27 days later. Some enthusiasts have attempted to pursue this time period, sometimes with success. Sunspots come and go, therefore this is anything but a foolproof strategy. Also, you will only be able to plan your holiday on short notice.