Originally Posted by Riot

Omen's threat values are accurate to the moment but in the context of an entire parsed encounter, somewhat irrelevant. What should be kept in mind is that when you parse threat using WWS, it's taking the encounter time from start to finish. Parsing the threat of your MT on Illidan for example, is meaningless because there's an entire phase of combat where Illidan's not a real actor - more like an environmental obstacle.