Predictability assessment of Heavy Precipitation Events observed during the HyMeX IOP16a based on Convection-Permitting Ensemble Systems

During fall the Western Mediterranean basin is very prone to high-impact
weather events such as heavy precipitation inducing devastating flash-flooding. One
major goal of the special observation period (SOP1) took place in fall 2012 is to
improve our ability to predict such high-impact weather events and their
consequences, which is still low due to the contribution of fine-scale processes and
their non-linear interactions with large-scale processes. For that purpose, the
development of convection-permitting ensemble systems (CPEPS), dedicated to the
study of the predictability of Mediterranean heavy precipitation, was part of the
modelling strategy during HyMeX SOP1.
This study compares and evaluates two CPEPS based on COSMO and
AROME models in the HyMeX framework. A probabilistic evaluation is conducted
over a 53-day period of the HyMeX SOP1. The two CPEPS, though different in their
characteristic, exhibit a good amount of probabilistic skill in forecasting heavy
precipitation at a relatively high spatial and temporal resolution. Therefore they can
be regarded as promising tools for operational forecast.
An analysis of the predictability of two heavy precipitation events observed
during the HyMeX intense observation period (IOP) 16a on 26 October 2012 is also
undertaken. For this IOP16a case study, the fine-scale surface precipitation
prediction is strongly sensitive to how mesoscale key features for deep convection
triggering are predicted in the CPEPS. Sensitivity experiments are also carried out in
order to examine the variability of such key mechanisms compared to different
perturbations applied in the CPEPS.