This workshop aimed to strengthen the links between observational campaigns and Numerical Weather Prediction (NWP) to (1) help observational campaigns optimise their use of forecasts and knowledge of forecast errors and (2) help NWP system development make better use of observational campaign data. Forecast errors in NWP, such as in the ECMWF forecast system, often motivate field campaigns, and forecasts are used in many ways during these campaigns. This workshop invited experts involved in recent or future campaigns that have made or will make use of ECMWF data to share their experiences and provide feedback on their use of ECMWF forecasts. The process of campaign planning, diagnostics and improved understanding of model errors, and ultimately the improvement of NWP systems will be key themes of the workshop.