Precipitation small, at the moment (4)
I believe the answer is:
snow
'precipitation' is the definition.
(snow is a kind of precipitation)
'small at the moment' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'at the moment' becomes 'now' (I've seen this before).
's'+'now'='SNOW'
(Other definitions for snow that I've seen before include "that may come at Christmas" , "TV newsman" , "Wintry flakes?" , "Winter weather" , "Ice flakes" .)