Long-term weather conditions (7)
I believe the answer is:
climate
'long-term weather conditions' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for climate that I've seen before include "Came lit (anag.)" , "Lime cat (anag.)" , "Mail, etc (anag.)" , "Long-term prevalent weather conditions" , "Atmosphere" .)