A method for forecasting power production of at least one wind turbine, the wind turbine forming part of a wind farm arranged at a site. Global weather forecast data is received at a central data centre. A site specific forecast is then generated at the central data centre, based on the global weather forecast data. The site specific forecast from the central data centre is sent to a local data centre, e.g. arranged at the site of the wind farm. Site specific data is received at the local data centre and comprises site specific weather data and/or site specific wind turbine data measured at the site. The site specific forecast is then updated at the local data centre, using the site specific data. Finally, a power production forecast of the at least one wind turbine is generated based on the updated site specific forecast.