They are mammatus clouds. I saw these after a storm this summer. Both pretty and a bit creepy!
Emily
I was going to say, they don't real at all! Going to have to google it now
LCT
#23 less pretty than super weird
PicklesMcGee
#24 is very beautiful
MNExpat
Mammutus clouds occur before a severe thunderstorm. They indicate severe instability in the atmosphere and usually mean hail. There name is derived from the Latin word for udder.