The extreme forecast index (EFI) concept has been applied to the European Centre for Medium-Range Weather Forecasts (ECMWF) seasonal forecasts (S4) of 2-m temperature (T2M) and total precipitation (TP) 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.
- Extreme forecast index
- Seasonal forecasts