I remember that when I used Geometric Weather (not developed anymore, its more known fork is called Breeze Weather) it had a option to notify me when it was going to rain, but know that functionality was removed from Breeze Weather, it's there any other app with this functionality?
Thank you so much! I used it some weeks ago and I swear that when I tried to select any precipitation provider it only shown me one that didn't have support for my country but now it seems fixed because it show me more providers.
Seconding Breezy, the app is way better than my phone's (OnePlus 9p) default weather app. They also have a wide variety of widgets, including some with Material You theming for Android 13+.
It's not open source but Rain Alarm draws a circle around you on the map and alerts you if weather radar detects any precipitation entering that circle. I don't know if that's what you want but it's what I want in a rain notification and it's the only app I'm aware of that does it.