The result of detailed analysis of the severe hailstorm of 7 June 1966 is presented. The storm caused more than 10 million dollar over wide area (Fig. 3). Synoptic conditions on this day were apparently favorable to the formation of severe convective storms in Kanto region (Fig. 1, 2, 13).
Although the information concerning to hailstroms on this day was not sufficient to locate all individual hailclouds, behavior of some of these are investigated in detail. It seems that at least 10 individual hail clouds were formed on this day. These are grouped into 4 systems. One of the system (No. IV) moved relatively dense surface observational network, thus allowed detailed examination of its structure.
This storm developed into an extraordinarily size, compared with most thunderstorms which develop in this area, within short time. The storm accompanied hail about 6 hours, the whole life time was more than 7 hours. Severe to moderate hail-damage occurred along its path for a continuous belt of 150km in length. Very intense rain was observed. 35.0mm in 10 minutes was an official record at the site of the Japan Meteorological Agency. Stronger rain, perhaps up to 50mm/10min, . might occur at some areas in Saitama Prefecture, north of Tokyo. Distribution of surface weather at 8pm shown in Fig. 10, reaveals that the storm structure was very much similar to a SR-storm dicsussed by Browning (1964). An interesting event occurred between 8pm and 9pm, namely, at 9pm the storm was already a squall mesosystem (Fujita, 1963) with several cells, some of them accompanied hail and intense rain. The transition form a single cell structure to a multi-cell system was apparent. It seems this change was related to weakening of the whole convective storm unit. Unfortunaely it was not possible to examine the course of this change because PPI pictures were available about one hour intervals. Most of the other hail clouds were small and the lack of data prevented detailed study of these storms.