Might, if there's a cold front about (5)
I believe the answer is:
force
'might' is the definition.
(thesaurus)
'there's a cold front about' is the wordplay.
'there's a cold' becomes 'c' (eg on taps).
'front' becomes 'fore' (fore is a kind of front**).
'about' is an insertion indicator.
'c' going inside 'fore' is 'FORCE'.
'if' acts as a link.
(Other definitions for force that I've seen before include "Impetus" , "Power; army" , "Body of e.g. police" , "Royal Air - -" , "Muscle" .)