This mod adds a singular block: The Weather Anchor.
Disclaimer: This mod is very experimental and probably won't be updated frequently.

Add Amethyst Blocks into the Weather Anchor's GUI, then click the weather you want. It consumes an Amethyst Block every time you change the weather. The weather should change, even if you don't have commands enabled. Currently, the Clear weather option executes the /weather clear 0 command, because /weather clear starts a thunderstorm about 5 minutes later.
Feel free to use this mod in your pack.
Made with MCreator :)