The purpose of this paper is to reconsider the “Synoptic Climatology” described by W. C. Jacobs and to interpret the local and small scale weather features. W. C. Jacobs intended to reduce the mean climatic picture, a fictitious average, into its component of actual weather patterns, classified the daily sea level series of historical weather maps for Far East Asia according to the derection of gradient air flow over the Hokkaido, and expressed the distribution of percentage frequency of days with precipitation amount for the preceding 6 hourly period greater than 1mm for each air flow pattern.<br> However, this classification is not suitable to all days. The direction of gradient wind over the Hokkaido is very difficult to determine by surface weather chart, as isobar has a degree of curvacure over the area of Hokkaido. Moreover, data of precipitation for 6 hourly period are too sparse to represent the detailed weather distribution.<br> In this paper, daily precipitation amounts were treated (the location of the stations was shown in fig. 2.).<br> Primarily, the daily sea level weather charts were classified into monsoon type and cyclonic one; secondly the former was classified into 16 direction of gradient flow at 850mb surface and the latter into several patterns by the path of cyclones.<br> Results were illustrated in figs. 3 and 4.;<br> Fig. 3. The percentage frequency distribution of days with daily precipitation amounts greater than 5mm for monsoon type.<br> Fig. 4. Only the following two example were shown, when daily precipitation amounts exceed 10mm, <br> (a) cyclone passing over Sakhalin and the associated cold fronts running over Hokkaido.<br> (b) cyclones advanced along the south coast of Hokkaido.<br> All of these charts show the detailed distribution of precipitation corresponding to the surface feature of topography and wind direction. For instance, heavy snowfall area in monsoon patterns moved from mountaineous region of southwestern Hokkaido (Shiribeshi District) to northwestern Hokkaido (Teshio Mts. Area) with the change of wind direction. The influence of Rishiri Island, pointed out by Mr. Suzuki on this volume pp. 321_??_326 is distinctly recognized<br> Then the distribution of computed values of precipitation intensity caused by orographical vertical motion with the west wind (fig. 5 (a) was compared with the percentage frequency distribution of precipitation amounts greater than 10mm with west wind (fig. 5 (b)). Generally speaking, the distribution pattern on both charts were similar, but heavy snowfall area was not coincident with each other, and its area in actual pattern was situated on the inner part of the mountaineous region. Furthermore, the paticular weather distribution was discovered in some parts on this chart, and therefore the typical weather feature over Ishikari Plain was illustrated on fig. 6, for west wind flow pattern at 850 mb surface. Stream lines drawn by cloud direction seemed to relate to weather distribution, discontinuous line between clear weather and snowfall region.<br> Finally, these results were applied to climatic variation. Three charts of fig. 7 showes the possibility of explanation of climatic variation by synoptic climatology. Figs. 7 (a), (b); January precipitation ratio in 1945 and 1953 to the normal, and discontinuous lines of January precipitation ratio during the period of 1941-1960.