Broadcast covering new wintry weather (4)
I believe the answer is:
snow
'wintry weather' is the definition.
(I've seen this before)
'broadcast covering new' is the wordplay.
'broadcast' becomes 'sow' (sowing is a kind of broadcasting).
'covering' is an insertion indicator.
'new' becomes 'n'.
'sow' enclosing 'n' is 'SNOW'.
(Other definitions for snow that I've seen before include "Weather feature" , "TV newsman" , "that may come at Christmas" , "author" , "Downfall of white" .)