|Title||The extreme forecast index applied to seasonal forecasts|
|Publication Type||Technical memorandum|
|Secondary Title||ECMWF Technical Memorandum|
|Authors||Dutra, E, Diamantakis, M, Tsonevsky, I, Zsótér, E, Wetterhall, F, Stockdale, T, Richardson, D, Pappenberger, F|
The Extreme Forecast index (EFI) concept has been applied to the ECMWF seasonal forecasts (S4) of 2-meter temperature and total precipitation using a novel semi-analytical technique. Results derived from synthetic data highlight the importance of large ensemble sizes to reduce the EFI calculation uncertainty due to sampling. This new diagnostic, complements current diagnostics, as exemplified for the 2012 warm summer in South Central and Eastern Europe. The EFI provides an integrated measure of the difference between a particular seasonal forecast ensemble and the underlying model climate which can be used as an early warning indicator.