Vortex SEASONAL uses Copernicus Climate Change Service (C3S seasonal forecast datasets, which are provided by European Centre for Medium-Range Weather Forecasts (ECMWF), the UK Met Office, Météo-France, the German Weather Service (Deutscher Wetterdienst, DWD), the Euro-Mediterranean Center on Climate Change (Centro Euro-Mediterraneo sui Cambiamenti Climatici, CMCC), the US National Weather Service’s NCEP (National Centers for Environmental Prediction, NCEP), and the Japan Meteorological Agency (JMA).
These models are initialized with data describing the system’s state at the starting point of the forecast, and then they are used to predict the evolution of this state over time. While ensembles can describe the uncertainties coming from inaccurate knowledge of the initial conditions of the components of the Earth’s system, uncertainty arising from approximations made in the models is very much dependent on the choice of model used. A convenient way to quantify the effect of these approximations is to combine outputs from several independently developed, initialized, and operated models.
Monthly wind speed anomaly forecasts are calculated as a percentage from monthly-mean forecasts over monthly-mean hindcasts (retrospective forecast). The retrospective forecasts are initialized at equivalent intervals over the period 1993-2016. The ensemble-mean anomalies are then computed concerning the corresponding model climate for each model.