Wired has a good and basic story about how NOAA produces La Niña watches and why they sometimes flip-flop on what they are expecting. You can read it at https://www.wired.com/2016/10/la-ninas-not-whatever-lets-la-nina-winter/.
https://www.wired.com/2016/10/la-ninas-not-whatever-lets-la-nina-winter/
