Numerical Weather Prediction (NWP) has significantly improved the accuracy of weather forecasts and enabled the development of services specifically for mariners, including routeing advice and forecasts as ECDIS overlays. But do mariners know enough about NWP and its limitations to rely on it for safe operations? Can they get the most out of it if they don’t understand how it works?

This practical guide answers those questions by opening up the technology that now forms the basis of all modern weather forecasts so that mariners can recognise when they are being presented with NWP, establish its source and the characteristics and performance of the particular NWP model and make informed judgements on suitability and use. Based on that understanding, the guide demonstrates how mariners can evaluate the added value of the many digital weather products and services on offer and also create their own forecasts using freely available NWP sources and free viewers.