The European Centre for Medium-Range Weather Forecasts (ECMWF) is an independent intergovernmental organisation supported by 34 states. ECMWF is both a research institute and a 24/7 operational service, producing and disseminating numerical weather predictions to its Member States. This data is fully available to the national meteorological services in the Member States. The Centre also offers a catalogue of forecast data that can be purchased by businesses worldwide and other commercial customers.
ECMWF is a world leader in data assimilation research and development. The quality of forecasts depends on how well usage of information received in real-time from the global observing system, which consists of numerous satellite instruments, weather stations, ships, buoys, and other components.
The purpose of data assimilation is to determine a best possible atmospheric state using observations and short range forecasts. Data assimilation is typically a sequential time-stepping procedure, in which a previous model forecast is compared with newly received observations, the model state is then updated to reflect the observations, a new forecast is initiated, and so on. The update step in this process is usually referred to as the analysis; the short model forecast used to produce the analysis is called the background.
Data assimilation also use to monitor climate change based on past observations – this is called reanalysis data.