Abstract
In summer, localized heavy rainfall in a short time on Kofu Basin is caused by a cumulonimbus cloud. We analyzed the characteristics of distribution and preceding surface conditions of cumulonimbus clouds appeared on Kofu Basin using X-MP radar and surface observation data from July to September in 2012. The frequency of the cumulonimbus clouds appeared on Kofu Basin was low. However, the rainfall amount brought by such a cumulonimbus cloud was large. The first appearance of cumulonimbus clouds concentrated from east side to center of Kofu Basin. Before the appearance of a cumulonimbus cloud, south-southwesterly wind with warmish and moist air from the inlet of the valley on southwest side of Kofu Basin and southeasterly wind with warmish and semimoist air crossing the mountains on east side of Kofu Basin co-existed at surface on Kofu Basin with warm and low moist air. The winds formed the convergence and the airs formed the conditional instability on Kofu basin, which formed the environment of the appearance of a cumulonimbus cloud on Kofu Basin.
