Eternal Winter

This small mod transforms any biome into a snowy landscape. By default, snow doesn't fall in oceans and rivers to prevent them from freezing over, but this setting can be changed in the EternalWinter configuration files.

When generating new chunks with the mod installed, they immediately become covered with snow. If you're loading an existing world, snow will only start accumulating after precipitation begins - old territories won't be automatically snow-covered.

Important advantage: the mod only needs to be installed on the server side. Biome changes are automatically synchronized with clients, even if they're running the standard Minecraft version without mods.