Recalibrating wind-speed forecasts using regime-dependent ensemble model output statistics

Abstract

Raw output from deterministic numerical weather prediction models is typically subject to systematic biases. Although ensemble forecasts provide invaluable information regarding the uncertainty in a prediction, they themselves often misrepresent the weather that occurs. Given their widespread use, the need for high-quality wind-speed forecasts is well-documented. Several statistical approaches have therefore been proposed to recalibrate ensembles of wind-speed forecasts, including a heteroscedastic truncated regression approach. An extension to this method that utilises the prevailing atmospheric flow is implemented here in a quasigeostrophic simulation study and on Global Ensemble Forecasting System (GEFS) reforecast data, in the hope of alleviating errors owing to changes in the synoptic-scale atmospheric state. When the wind speed depends strongly on the underlying weather regime, the resulting forecasts have the potential to provide substantial improvements in skill relative to conventional post-processing techniques. This is particularly pertinent at longer lead times, where there is more improvement to be gained over current methods, and in weather regimes associated with wind speeds that differ greatly from climatology. In order to realise this potential, an accurate prediction of the future atmospheric regime is required.