Form of precipitation (5)
I believe the answer is:
sleet
'form of precipitation' is the definition.
(I know that sleet is a type of downfall)
This is all the clue.
(Other definitions for sleet that I've seen before include "Rain/ice mix" , "Partly melted falling snow or hail" , "Partly frozen rain" , "unpleasant weather" , "Snowy rain" .)