Abstract: With the isentropic coordinates system we have calculated many synoptic types (perpendicular motion) of precipitation of the (objective analysis) model atmosphere of T₁₀₆L₁₉ in June and July 1998. Two types of synoptic (scale) precipitation are condensation function and moisture flux divergence that have their positive and negative distributions and are both continuous "waves" (called precipitation and inverse precipitation). There are two more types of a mass moist-unstable precipitation and an air layer moist convection precipitation in the atmosphere,which have their selective-random characters. This paper has made it known that there will be two above-mentioned types of Mei-yu Front's precipitation above the Yangtze River's basin. And the moist air masses maintain long time and transport rapidly, and the non-isentropic saturation-adiabatic process comes into being moist convection precipitation, that is the synoptic causes of the rain gust. Therefore, with a few factors of precipitation of the forecast model atmosphere, which are continuous fields, it has been possible to forecast actual precipitation of real atmosphere with statistical & probable method (include Kalman filter). So linearization on statistics between the predictors and the predicated has come true in fact.