Rain or snow (11)
I believe the answer is:
precipitate
This clue is a double definition.
'rain' is the first definition.
(I know that rain is a more specific form of the action precipitate)
'snow' is the second definition.
(I know that snow is a more specific form of the action precipitate)
(Other definitions for precipitate that I've seen before include "Pour" , "Cause (a bad event) to happen prematurely" , "Accelerate" , "Reckless" , "Done without careful consideration" .)