NWP models have to cover a large spectrum of atmospheric scales, from the global long waves down to kilometric scales. The models are generally built around a dynamical core together with several physical parametrizations which represent subgrid processes inside the atmosphere and interaction processes with its environment. Operational NWP models are also constrained by real-time requirements, computing resources and the necessity to assimilate observations regularly. Moreover NWP models are systems which are often used for climate modelling and re-analysis.

This session is expected to focus on the above points and to gather presentations and posters on the following topics:
• general aspects of numerical schemes in NWP models;
• physical parametrizations and their interaction with a dynamical core;
• the challenges coming from the need to model a larger and larger ensemble of scales as well as more and more detailed basic processes;
• more specifically the need to model the convection and to handle the "grey zone" (transition from synoptic-scale to convective-scale modelling);
• the challenges coming from the need to produce efficient models on massively parallel computers;
• techniques for quantitative precipitation forecasting aiming to the achievement of the greatest possible benefit in subsequent hydrological forecasts;
• the evaluation, validation, criticism and intercomparison of different numerical and physical schemes.

The main focuses of this session are the interactions between parametrizations and the dynamical core, or parametrizations among themselves, in a NWP context.