It's just as simple as it sounds, rain in the desert. It's definitely an oversight on Mojang's part that it can't rain in deserts or in any "dry" biome, ever. If you've ever wanted to experience a desert monsoon in Minecraft, just install this datapack onto your world. Don't fret if you don't live specifically in a desert because this datapack adds rain to all dry biomes such as savannas, savanna plateaus, badlands, wooded badlands, eroded badlands, windswept savannas and of course, deserts. This datapack is technically flagged as experimental because it uses the world generation feature of datapacks to change the biome temperature and precipitation, but I've thoroughly tested this datapack and it does not affect world generation whatsoever. I use this datapack on my own survival world as my base is in a savanna/desert and I like being able to experience thunderstorms in the desert. Removing this datapack from your world won't corrupt it, but always be prepared anyways and make backups.

INSTALLATION/REMOVAL:

To install the datapack, just drag and drop the ZIP file into your world's datapack folder. To uninstall it, in-game open the world to LAN and enable cheats if they're not already on, and do /datapack disable and then the file name of the datapack, and then remove it from the datapack folder.

NOTE:
The version compatibility with this datapack is very important, when major updates release I will try to update this datapack as fast as possible, but any versions outside the version compatibility parameter won't work. If an update adds new ores or structures to the game, then I need to update that in the datapack so don't use this datapack on a version outside the parameter or else your dry biomes may generate incorrectly.