Truncated is an adjective that means "cut short," like a truncated picnic, caused by the sudden downpour.
The word comes from the root truncate, which is of Latin origin, and means "cut off." When an object is truncated, its end or point is cut off, like a truncated arrow that is safe for kids to play with. Truncated can also refer to something that ends earlier than planned — everyone was angry at the truncated concert until they learned that the singer had broken his leg when he fell on stage.