Tendency for snow to pile up (5)
I believe the answer is:
This clue might be a double definition.
'tendency' is the first definition.
(I know that drift is a type of tendency)
'pile up' is the second definition.
(I know that drift is a type of pile up)
'for snow to' is the link.
This may not be correct. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for drift that I've seen before include "Walk casually; snow pile" , "Tendency" , "Gist - snow" , "Bank (of snow)" , "non-standard deviation?" .)