Where should I look to make it snow?
it’ll become clear after you obtain journal entry 15. Obtain it, solve it, make it snow.
Also, just discovered the knowledge you gain from trees only actually works if you create a save after obtaining. Player knowledge is not enough, apparently. Even having a journal entry (but not reading it) can prevent you from crafting something despite knowing the recipe.
It involves the tree that wants the Lilyth. Once you can properly handle one and talk to it, I believe it tells you about something underneath it. If you didn't get the hint after showing it the Lilyth the tree then becomes the one that slaps your butt. The tree that gives you the Crusty Key is the tree you are looking for.