Slight fog starts to roll away over lake — there's a wind (7)
I believe the answer is:
mistral
'there's a wind' is the definition.
(mistral is a kind of wind)
'slight fog starts to roll away over lake' is the wordplay.
'slight fog' becomes 'mist' (I've seen this before).
'starts to' suggests taking the first letters.
'over' is a charade indicator (letters next to each other).
'lake' becomes 'l'.
The initial letters of 'roll away' is 'ra'.
'mist'+'ra'+'l'='MISTRAL'
(Other definitions for mistral that I've seen before include "That's a blow" , "Famous wind in the Rhone Valley blowing towards the Med" , "French wind" , "Violent northeast wind of southern France" , "Cold dry wind in southern France" .)