Second article in French about climb in good weather (8)
'good weather' is the definition.
'second article in french about climb' is the wordplay.
'second' becomes 's' (common abbreviation).
'article in french' becomes 'une' (an indefinite article in French).
'about' is an insertion indicator.
'climb' becomes 'shin' (shinning is a kind of climbing).
'une' placed around 'shin' is 'unshine'.
'in' is the link.
(Other definitions for sunshine that I've seen before include "Brightness", "Daily light and warmth", "Light, cheerfulness", "Cock", "term of address".)