The month's weather forecast for the London area (7)
I believe the answer is:
mayfair
'the london area' is the definition.
(I've seen this before)
'the month's weather forecast' is the wordplay.
'the month' becomes 'may' (May is an example).
'weather forecast' becomes 'fair' (I've seen this in another clue).
'may'+'fair'='MAYFAIR'
'for' is the link.
(Other definitions for mayfair that I've seen before include "West End area" , "expensive area of London" , "smart residential district" , "Wealthy London district" , "Affluent London area" .)