Given the nonlinear and complex nature of atmospheric system combined with the uncertainties associated with initial conditions and models, it is not only a requirement from science but also a necessity to better serve user community to transit weather prediction from deterministic to probabilistic format. However, the rational behind the transition is not clear but full of debate and confusion to many including public, endusers and even meteorologists themselves. To clarify some of these and to expedite the transition, a few issues were discussed. Since the ensemble forecasting is a central technique to facilitate such a transition, it is first discussed in this paper by focusing on the following five aspects: (1) why is ensemble forecasting needed? (2) what is the primary mission of ensemble forecasting? (3) what are common misunderstandings about it? (4) what is the impact it will bring to numerical weather prediction system as a whole? and (5) what is the forecaster’s new role in the “ensemble forecasting” era?