Modern truths about violent weather (12)
I believe the answer is:
thunderstorm
'violent weather' is the definition.
(I've seen this before)
'modern truths about' is the wordplay.
'about' indicates an anagram.
'modern'+'truths'='moderntruths'
'moderntruths' with letters rearranged gives 'THUNDERSTORM'.
(Other definitions for thunderstorm that I've seen before include "Bad weather" , "Occasion for lightning" , "Loud and violent gale" , "Loud flashy display" , "Violent weather" .)