Numerical Weather Prediction (NWP) is essentially how we use computers to help forecast the weather. Today some of the most powerful super-computers in the world are dedicated to weather forecasting and climate applications. In this episode, Dr. Alan Hally from the Research Division in Met Éireann joins Liz and Noel to talk about the concepts behind using computers to forecast the weather, how accurate they have become and what the limiting factors are in terms of scale and forecast duration. Can they tell us if we will get a white Christmas this year?  In addition, what is the connection between NWP and Jurassic Park? We get an explanation from Jeff Goldblum on 26 minutes. We also hear about Met Éireann’s ‘Harmonie Arome’ weather forecasting model and its three million lines of code, and Ireland’s international collaborations in super-computing and forecasting technology. We discuss the ‘butterfly effect’ and how chaos in the atmosphere affects our forecasts, and talk about ensemble prediction systems and how they are changing our perception and delivery of weather forecasts.  Paul Moore from our Climate Division brings us the stats for summer 2019 and we discuss how and why summer 2019 differed from summer 2018. As always, the Met Éireann choir – The Isobars – close out the episode. This month they perform their rendition of The Swimming Song.