In every cliff there is no snow and if I set the weather to rain, it doesn't snows but it rains.
Demonstration video:
(if the video doesn't show, the link is https://imgur.com/a/OItJc6i )
I need help as soon as possible, because I need to use this mod in my modpack.

It was intentional that this happened, however in the latest update I added Snowy Cliffs which spawn in Snowy climates which have snow on them.