This study investigates the dynamical characteristics associated with abnormal wet summer over the Korean peninsula in 2003. The effects of external forcing such as sea surface temperature, soil moisture, sea ice, snow, etc on an East Asian summer monsoon are also studied. Another simulation with initial condition for a normal year has been examined. Each simulation has been performed with 5 member ensembles using the National Centers for Environmental Prediction (NCEP) global spectral model (GSM). The preliminary result show that a negative snow anomalies in Tibetan Plateau (TP) during November 2002 – March 2003 are related to the lower surface albedo and positive tropospheric atmospheric temperature anomaly over TP, strong land-sea thermal contrast. Reduced TP snow is also related with the reduced soil moisture over China. A comparison of sensitivity experiment with various external forcings will be investigated in more detail.