This talk presents a newly developed atmospheric model system, the YOnsei University Research model System (YOURS), which has a great flexibility with multi-platforms with either thread mode or message parallel modes. The dynamical core of the YOURS-Global Spectral Model (GSM) can be either spherical harmonics (SPH) or double Fourier spectral (DFS) (Cheong 2006). The system also has multiple options in each physics parameterization, with newly devised algorithms. The YOURS-GSM has been widely evaluated for seasonal simulations as well as weather prediction. This talk will focus on the effects of improved physics on the simulated seasonal climatology, focusing on the interaction between the boundary layer and precipitation physics. Some uncertainties in dynamical downscaling using regional models will also be discussed.