From the view of nonlinear theory,the three types of atmospheric motions issued by von Neumann(1955) are re-explained,and it is pointed out that in the prediction of atmospheric processes there exist two kinds of uncertainties-uncertainties in initial conditions and uncertainties in external forces,which become the studied objects of the first kind prediction and the second kind of prediction,respectively.In this paper,the objectivity in the predictability of atmospheric processes is emphasized.Owing to the complexity of atmospheric motions and the limitation of observation skill and knowledge of human being,the predictabilities of atmospheric processes can only be estimated.For example,the upper limit of daily weather is estimated to be about two weeks.The sources of prediction errors-the uncertainties in initial conditions and the imperfectability of prediction models are analyzed,and it is emphasized that the essential reason of prediction error growth is the chaotic character of atmospheric motions.