Forecaster interrupted by second news boss loses cool (4,3)
I believe the answer is:
sees red
'loses cool' is the definition.
(both can mean becomes angry)
'forecaster interrupted by second news boss' is the wordplay.
'forecaster' becomes 'seer' (someone who sees the future).
'interrupted by' indicates putting letters inside.
'second' becomes 's' (common abbreviation).
'news boss' becomes 'ed' (I've seen this in other clues).
'seer' enclosing 's' is 'seesr'.
'seesr'+'ed'='SEES RED'
(Another definition for sees red that I've seen is " 'Becomes colourfully angry (4,3)'".)