I think if you spend your whole day outside, the weather could/should be a more important thing
(and it would also be nice to add some relevance to the wetherlore skill)
In addition to those cool things already on the development list:
Varying forms of snow
The amount and the form of snow having more impact on physical activities the character, NPCs and animals can do
Ability (and sometimes a need) to remove snow (by shoveling)
Thunder and lightning
Storms; trees felling down, crops getting hurt etc.
Growing plants reacting to the weather and flourishing accordingly
what do you think about:
Fog, hindering your range of sight, down to just a few meters also during the day in extreme conditions
so for example there could be some foggy autumn weeks that make hunting really weather dependant
modelling the moon as influence on range of sight during the nigth (a full moon night in winter can feel bright as a day, just without colors)
this would be influenced by weather too.
i dont know if there was a spiritual connection to the full moon in finland, but i guess there was, like in most old cultures
different levels of wind, that effect your temperature and you risk much faster freezing when going out on windy days in the winter
maybe it could also effect how close you can sneak up to a herd of reindeers, depending on direction of the wind
old men in villages beeing able to tell you more about the weather than your weatherloreskill, like early warnings from storms.
clothes getting wet, then getting heavy and lose warmth until they are dried by time or a fire
I dont know how the weather in Finland really is, as i am coming from the alps, so if there are misconceptions tell me please
PS: I love this game and appreciate every minute put in its developement