A fork has appeared that provides more functionality than this plugin, check it out: AntiBlockFade

The Description:

I've been trying to build a christmas themed map that is very much lightened, but snow always melted. I didn't want to use the blocks that didn't melt snow, and I also didn't want to install worldguard to set some weird region and prevent snow from melting. So, I just wrote this plugin that does so globally.

This plugin wasn't tested in any other server besides my own. I have no idea if this plugin works in just one world or all of them. I suspect that it works in all worlds. I may update this plugin in the future so that users could actually set where this plugin works and where it shouldn't.

This plugin can potentially work in older versions, but I haven't tested any other version besides 1.21.1.
In any case, That's about it for the plugin.

Commands:

/preventsnow <true/false>

Permissions:

preventsnow.toggle - Players that have this permission can use the /preventsnow command.

Default: op