I've only just recently joined this depressing fandom and i don't know all the theories and little things in GO but this is just my thoughts
.. so after azi leaves him, crowley goes through depression and anger and all of that jazz and since he affects weather based on his emotions, he starts unintentionally making the weather so much worse and starting fights/wars around wherever GO is based in. and the humans from s1/2 have to stop him or smth. and maybe aziraphale sees the destruction on earth too 🤐😀 ok thanks i hope you guys find some nightingales