  One of the main goals of the feasibility study MOSE (MOdellig ESO Sites) is
to evaluate the performances of a method conceived to forecast the optical
turbulence above the ESO sites of the Very Large Telescope and the
European-Extremely Large Telescope in Chile. The method implied the use of a
dedicated code conceived for the optical turbulence (OT) called Astro-Meso-Nh.
In this paper we present results we obtained at conclusion of this project
concerning the performances of this method in forecasting the most relevant
parameters related to the optical turbulence (CN2, seeing , isoplanatic angle
theta_0 and wavefront coherence time tau_0). Numerical predictions related to a
very rich statistical sample of nights uniformly distributed along a solar year
and belonging to different years have been compared to observations and
different statistical operators have been analyzed such as classical bias, RMSE
and and more sophisticated statistical operators derived by the contingency
tables that are able to quantify the score of success of a predictive method
such as the percentage of correct detection (PC) and the probability to detect
a parameter within a specific range of values (POD). The main conclusions of
the study tell us that the Astro-Meso-Nh model provides performances that are
already very good to definitely guarantee a not negligible positive impact on
the Service Mode of top-class telescopes and ELTs. A demonstrator for an
automatic and operational version of the Astro-Meso-Nh model will be soon
implemented on the sites of VLT and E-ELT.
