SilverJakler

It can change when you enter a new region, or after several days have passed. If you're looking for a reliable way to control it, you can try this:

It includes the option to set the weather you want via your pokégear, among many other QoL features.

Thanks, dude. This'll be real helpful considering I'm trying to train a Growlithe and there's been nothing but thunderstorms and rain out lol