Sudden, striking (8)
I believe the answer is:
dramatic
I believe this is a double definition.
'sudden' is the first definition.
(thesaurus)
'striking' is the second definition.
(I know that striking can be written as dramatic)
(Other definitions for dramatic that I've seen before include "Substantial" , "Like play" , "Striking, impressive" , "spectacular" , "with eye-popping effect!" .)