In order to see the Northern Lights, you need 3 things:
- It needs to be (semi) dark outside,
- It has to be (partially) clear sky,
- There need to be Northern Lights activity.
While number 2 and 3 are very difficult (if not impossible) to predict accurately, number 1 is a little easier to answer. Since Tromsø has the midnight sun, it is impossible to see the Northern Lights between mid-April and late August. Between late August and early April it is dark enough at night to see the Northern Lights. In the first and last few weeks of this period, the nights are shorter so the chances are a little lower to see the Northern Lights.
Other than that, we believe that no particular month is better to see the Northern Lights than another. There are some other things to consider: September and October are usually without snow and less cold, while between mid-November and mid-January we have polar night and it is dark earliest. February and March often have more snow.
What is more important and has a bigger impact on your chances of seeing the Northern Lights is how long you are staying in Tromsø.