Clement, nearly six-week period keeping Spain cool to the north (7)
I believe the answer is:
lenient
'clement' is the definition.
(similar in meaning)
'nearly six-week period keeping spain cool to the north' is the wordplay.
'nearly six-week period' becomes 'lent' (I've seen this in another clue).
'keeping' is an insertion indicator.
'spain' becomes 'e' (abbreviation for Espana).
'cool' becomes 'in' ('in' can mean fashionable or cool).
'to the north' says the letters should be written backwards (in a down clue, letters go up or 'northward').
'e'+'in'='ein'
'ein' written backwards gives 'nie'.
'lent' placed around 'nie' is 'LENIENT'.
(Other definitions for lenient that I've seen before include "'Indulgent, easy (7)'" , "Forbearing" , "Forgiving, gentle" , "Showing tolerance" , "Tolerant, rather than strict" .)