Stockholm is close to the Baltic Sea, so pressure is often fluctuating, which means fluctuating temperature and weather conditions. So it's rarely warm or cold for a longer period of time. You might have visited Stockholm during one of those temperature highs. Average daily high in January is -1 in Stockholm, and -3.4 in Tampere. Not a huge difference, but Tampere is far more inland than Stockholm, so there's an explanation for that. And Stockholm is about 200km south of Tampere. Makes a difference too. Stockholm is about as far south as Tallinn.