Sudden downpour (6)
'sudden downpour' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cloudburst that I've seen before include "storm" , "dramatic downfall" , "Sudden, heavy downpour" , "sudden shower" , "Sudden rainstorm" .)
(Other definitions for squall that I've seen before include "Sudden brief storm" , "Sudden storm of wind and rain, or a baby's cry" , "Sudden strong wind" , "Brief violent storm" , "Yell" .)