Sometimes we have wetter conditions during La Nina winters in California, so dry conditions aren't set in stone.  ENSO is important as a prediction tool for California, but it is not the entire ballgame.  Here's an example of one memorable wet La Nina winter:

https://www.climate.gov/news-features/blogs/enso/why-did-it-rain-so-much-california-during-last-year’s-la-niña

CPC's seasonal outlooks are in terms of probabilities (percent chance that something will happen) and it's never anywhere close to 100%.  La Nina offers a hedge in the direction of certain future outcomes, but not a guarantee.  Check out NOAA CPC's seasonal outlook which is updated on the 3rd Thursday of each month here (click the links that say X-month outlook):  https://www.cpc.ncep.noaa.gov/products/predictions/long_range/