Weather when sun god is not out? (4)
I believe the answer is:
rain
'weather' is the definition.
(I know that rain is a type of downfall)
'sun god is not out?' is the wordplay.
'sun god' becomes 'ra' (Egyptian god).
'is not out?' becomes 'in' ('in' is the opposite to 'out').
'ra'+'in'='RAIN'
'when' is the link.
(Other definitions for rain that I've seen before include "Cats and dogs?" , "Falling moisture" , "bad weather" , "Precipitation" , "See 12" .)