As Michelle mentioned in the previous reply, climate outlooks are probabilistic in nature. And it is very rare (hasn't happened yet) that you would see a 100% chance of dry/wet or cold/warm than normal where you would know right away that the forecast "failed". In order to verify these sorts of forecasts to determine whether they have any skill above guessing you have to play the long game and look at how these outlooks performed over a longer period of time. I wrote three pieces for the ENSO blog on just how we verify these forecasts. I recommend giving them a look.  Part 1, Part 2, Part 3.