Snowstorm aftermath (5)
I believe the answer is:
'snowstorm aftermath' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slush that I've seen before include "Partially melted snow" , "Half-melted snow" , "that has been frozen" , "Sentimental drivel" , "Partly melted snow" .)