Some heavy rain for us after low pressure (8)
I believe the answer is:
downpour
'some heavy rain' is the definition.
(I've seen this before)
'for us after low pressure' is the wordplay.
'for us' becomes 'our' (I've seen this in other clues).
'after' says to put letters next to each other.
'low' becomes 'down' ('down' can be a synonym of 'low').
'pressure' becomes 'p' (abbreviation).
'down'+'p'='downp'
'our' after 'downp' is 'DOWNPOUR'.
(Other definitions for downpour that I've seen before include "Cloudburst" , "Heavy continuous rainfall" , "Deluge" , "Heavy fall of rain" , "Big fall makes" .)