Hello,
Thanks for answering. I tried to disable Cathedral Landscapes but it doesn't remove the snowy areas.
Here are some screenshots (I disabled grass to better show the landscape).
Something strange is that, despite "Landscape Identification by Terrain Texture" mod being enable, the name of the snow texture doesn't show. It seems that it is not directly landscape which is textured but an overlapping mesh dynamically added. I thought to Better Dynamic Snow, but adding it to a mod-clear version of the game does not make these areas appear and I believe that BDS only modifies textures, it does not add meshes.