Try to modify vanilla weather particle density, or integrated compatible with Particle Rain
https://github.com/PigCart/particle-rain/blob/542539976db5c8c1cd7c2a33b66fae6dafa42f22/src/main/java/pigcart/particlerain/WeatherParticleSpawner.java#L44

Needs adjust rainy clouds shape first, because clouds no cover the most part of sky often when rain. If make this issue impl, maybe no rain comes from sky.

if youre still having trouble with this you could take inspiration/ ask for help from the author of https://modrinth.com/mod/head-in-the-clouds