Abstract
Based on the analyses of weather maps of scales from local through Asiatic to northern hemispheric, the author studies in this paper some mesoclimatological problems of the mesoscale disturbances observed during the period of heavy snow in the Hokuriku District. The main problems treated are as follows:-
First, the statistical characters of the so-called plain heavy snow free from mountain effect and of mountain heavy snow are examined. According to the statistics on the frequency of heavy snowfalls for 9 winters from 1953 to 1961, mountain heavy snow is the most frequent, accounting for more than half of the total occurrences. On the contrary, the frequency of plain snow is comparatively low, as the mean occurrence of plain snow is only 2.5 days during one winter season. Plain heavy snow is mainly related to the bulge of isobars on the weather chart in which a cold vortex is located over the Japan Sea. Especially it seems that, under the prevalence of the bulge pressure pattern, there occur heavy snow and rainfall, thunderstorms and gusts with the passing of a mesoscale disturbance, throughout the year. Therefore this pressure pattern has great importance in forecasting severe storms around the Japan Sea side of the Japanese mainland.
