What could be an improvement in the weather (4)
I believe the answer is:
thaw
'weather' is the definition.
(thaw is a kind of weather)
'what could be' is the wordplay.
'could be' indicates anagramming the letters.
'what' is an anagram of 'THAW'.
'an improvement in the' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for thaw that I've seen before include "Melt; John --, actor" , "Become liquid" , "Frost going" , "when the temperature rises?" , "Melt in heat" .)