Dark clouds, perhaps (4)
I believe the answer is:
omen
'dark clouds perhaps' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for omen that I've seen before include "Prognostication" , "Portent, prophetic indicator" , "Sign of something about to happen" , "Sign of something to come" , "Harbinger, prophetic sign" .)