I believe someone wanted to create something like what you’re trying to do before. I don’t know of a device that has that attribute ‘rain’ or something similar that we can use to figure out if it’s raining.
Now, if you’re the McGyver kind… maybe you can make on of the one below and now put the two ends of the wire on each end of a half piece of pvc that’s slanted slightly so that water will flow one direction. If water is flowing, the wires will be shorted (raining), once it stops, the circuit will break (no more rain) lol. I don’t know how accurate it would be but that’s one way to skin this cat
