Extreme rainfall prediction using the European Centre for Medium‐Range Weather Forecasts ensemble prediction system

Abstract

The combined use of the European Centre for Medium‐Range Weather Forecasts high‐resolution, at T213 spectral triangular truncation and with 31 vertical levels (T213L31, operational model and ensemble prediction system (EPS), during cases of intense Mediterranean storms, is studied. In particular, it is discussed how EPS products can be used to provide a measure of confidence in the high‐resolution precipitation forecast. Three case studies (two extreme events plus one false alarm case) are analyzed. For the first two cases, the EPS probability values for precipitation occurrence supported the medium‐range T213L31 prediction, which proved to be successful. By contrast, for the third case, the high‐resolution forecast suggested heavy rainfall over northern Italy but was not supported by the EPS. The T213L31 prediction for this case was poor. EPS forecasts of extreme weather events are necessarily compromised by the moderate resolution of the T63L19 model (a version of the operational high‐resolution T213L31 model, at T63 spectral triangular truncation and with 19 levels) used to generate the ensembles. In future studies, ensembles will be made using at least T106L31 resolution combined with an increase in ensemble size.