Radio report’s failed to notice obscurity (4)
I believe the answer is:
mist
'obscurity' is the definition.
(thesaurus)
'radio report's failed to notice' is the wordplay.
'radio report's' shows a homophone (sound like) (how it might sound on the radio).
'failed to notice' becomes 'missed' (to miss something is to fail to notice it).
'missed' sounds like 'MIST'.
(Other definitions for mist that I've seen before include "Watery film" , "Mizzle; light rain" , "Obscure" , "Watery vapour" , "Think fog or low cloud" .)