Cold air turning warm (7)
I believe the answer is:
cordial
'warm' is the definition.
(similar in meaning)
'cold air turning' is the wordplay.
'turning' is an anagram indicator.
'cold'+'air'='coldair'
'coldair' is an anagram of 'CORDIAL'.
(Other definitions for cordial that I've seen before include "Hearty - drink" , "Warm and friendly; drink" , "Pleasant - soft drink" , "drink with a fruity flavour" , "Friendly; fruit drink" .)