If you want to see the Northern Lights (Aurora Borealis), it's best to travel to Lapland, where the lights are brighter. The Lights are not connected to temperature or weather, but your chances of spotting them are much better in winter, due to the long, dark nights, and they are especially active in March and September. The auroras follow the 11-year sunspot cycle, and are the most active around the cycle's peak. The last peak was in 2014, and the next is is 2025, so the lights are currently becoming stronger and more frequent, and will peak from 2023 to 2027. As the result of solar weather, the Lights are hard to predict, but various organizations track the solar wind to make predictions, which you can view in several places, such as here.