This is a pretty specific and borderline nitpicky topic, but hear me out. Instead of focussing on what authors might do that is “wrong” or “doesn’t make a lot of sense”, I’m going to give options, explanations, and things to consider. I’m also going to focus on it from character perspective even though this is a worldbuilding topic.
Northern environments in fantasy worlds is often used in fantasy writing. Lots of the action happens there. Why, I don’t know, but I dig it. So we’re going to go into stuff that might help shape your northern environments.