Abstract: From a large number of operational numerical predictions with the barotropic model, it is found that the, development of the pressure systems at 500 mb isobaric surface can sometimes be,well oredicted to. some extent, even though the zonal current is nredominent in the initial stream. tielcl. Vn the other hand, It is well-known from synoptic experience that the developinecit.of pressure pattern is closely related to the, change of curvature vorticitv and shearing vorticitv. Therefore, for the sake of investiaatina the proniem of aeveiopment,two equations for preaicang the two quantities are aerlvea. It can be shown that each of them is not conservative and, they can be transformed into each other in confluent.or defluent stream region under certain circumstances, regardless of the effect of variation of Coriolis parameter with latitude.From these results, the phenomena previouslyo mentioned may be explained. Finally, for the purpose of practical use, some rules for weather prediction are proposed」herefrom.