Weather data filter left by day attached to zip lines (8)
I believe the answer is:
rainfall
'weather' is the definition.
(rainfall is a kind of weather)
'filter left by day attached to zip lines' is the wordplay.
'filter' becomes 'drain' (I've seen this before).
'left by' indicates named letters should be taken away (word is left or abandoned by specified letters ).
'day' becomes 'd' (abbreviation for day).
'attached' says to put letters next to each other.
'to zip lines' becomes 'fall' (I can't explain this - if you can you should give a lot more credence to this answer).
'drain' with 'd' taken out is 'rain'.
'rain'+'fall'='RAINFALL'
'data' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for rainfall that I've seen before include "Shower" , "Form of precipitation" , "Water falling in drops" , "Amount of water coming down" , "Climate measure" .)