Go outside or look at the sky through your window and repeat this spell:
" God of the sky, hear my plea, make it cloudy, for me and for thee, now mote it be!"
This spell should work in 12 hours or less. If you want a faster spell, then search one up in this website because they have one that will take less time. You would do this one if you want to go outside know, but want it to rain later.
