Abstract: By an analysis of local temperature change on different isobaric surfaces,it is pointed out in this study that a three parameter model is often neccessary for prediction of major weather development.A case of the formation of blocking situation west of Ural is studied.The tendency computed with a three parameter model is in good agreement with the observed tendency during the critical moment of the formation of the blocking over that area,which is not foretasted by a ore or two parameter model.A forecasting rule is found by solving the equations for the three parameter model approximately.It states that the height of an isobaric surface rises when cold (warm) advection inereases (decrases) upward,and falls when the cold (warm) advection decreases (increases) upward.The neccessity and difficulty for higher approximation to the true wind is discussed.It is found that the available wind data given in the present code is not sufficiently accurate for the direct evaluation of the wind divergence,In solving Poisson equation a pattern of group relaxation is designed.