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Seasonal forecasts and the Copernicus Climate Change Service (C3S)

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The C3S seasonal forecast products are based on data from several state-of-the-art seasonal prediction systems. Multi-system combinations, as well as predictions from the individual participating systems, are available. The centres currently providing forecasts to C3S are: ECMWF, The Met Office and Météo-France, Deutscher Wetterdienst (DWD), Centro Euro-Mediterraneo sui Cambiamenti Climatici (CMCC), National Centers for Environmental Prediction (NCEP) and , Japan Meteorological Agency (JMA) and Environment and Climate Change Canada (ECCC), and you can find the details about when each system was introduced in the information contained in the Summary of available data.

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• fixed hindcasts. Some systems are designed so their expected lifetime will be around 4-5 years. Once the system has been designed and tested, ensemble hindcasts for the whole reference period are run. The advantage is that this reference dataset is available well in advance of real-time forecasts being issued, and its properties (biases, skill) can be quantified once for repeated use. As this is a very expensive exercise, it cannot be repeated too often and thus the system remains fixed for a long period of time.
• on-the-fly hindcasts. Some systems prioritise more frequent upgrades, which means that the hindcast sets have to be run more frequently. To achieve this in practice, the full hindcast set is run every time a new real-time forecast is produced, slightly in advance (a few weeks) of the real-time forecast and using exactly the same version of the forecasting system. This also offers the advantage of balancing the requirement for computing resources, but the compromise is the regular change of the model climatology.

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