The Sims 3 has a persistent world. The Sims 4 does not.
If you want dynamic snow that has perceived depth then you have to potentially rebuild a scene each time you travel - ie to a nightclub, to The Goths house, back to your Sim's house.
What happens when you play the Sims? Time passes.
You have to rebuild scenes to do this because the world is not persistent.
The notion of snow gathering on roofs, etc is easy - but it cannot be done on-the-fly like it is with The Sims 3. There is no way of doing it other than when loading a scene, calculating/re-calculating snow and then displaying the scene.
EDIT:
ie, how are you simulating snow on lots that are not resident - ie loaded - ie visible?
If the snow is thawing outside a lot and you then travel to The Goths' house then it has to be re-calculated - it may have been summer when you last visited The Goths - every time you go back to their house during snow periods, you will have to recalculate the weather - in terms of actual snow depth, coverage, drift, etc.
