Ruh-roh!
https://archive.org/stream/un-1976-weather-weapon-treaty/UN_1976_Weather_Weapon_Treaty_djvu.txt

I'd share the link on the UN website but the versions I find have been.. edited.. since the last time I cited them

The adorable bit is, this only applies to using it against foreign cuontries, with no regard for domestic use

Various states in the US have their own departments dedicated to this, for just one example:
https://www.tdlr.texas.gov/weather/