It’s pouring rain when you wake up (4)
I believe the answer is:
stir
'wake up' is the definition.
(I've seen this in another clue)
'it's pouring rain when you' is the wordplay.
I cannot quite understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
The remaining letters 'sir' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for stir that I've seen before include "Mix the ingredients" , "Ladies' underwear" , "Wake; disturbance" , "What keeps those inside" , "Detention centre" .)