What variation in the weather! (4)
I believe the answer is:
thaw
'weather' is the definition.
(thaw is a kind of weather)
'what variation' is the wordplay.
'variation' indicates an anagram.
'what' anagrammed gives 'THAW'.
'in the' is the link.
(Other definitions for thaw that I've seen before include "De-ice" , "get warmer" , "detente" , "Become friendlier; melt" , "Melt in heat" .)