HANYU, Juro

The hail precipitated in the large extent of Kanto Plain in April 24th, 1985. The damage reached about 500, 000, 000 yen which was less than expected from the strength and the scale of the hail precipitation. One of the reason is that it occurred in the early cropping season. In this study, meteorological factors on this hail event were analyzed with paying attention to the forecast of hail precipitation, because the strength and the scale were so large. As the results, following features were found: 1. Arrival of the upper cold air mass could be predicted by using the movement speed of the 500mb height air mass over the continent. 2. In the day of the hail precipitation, the convective instability of air column existed upto 3000m height from the surface. The lower layer than lOOOm height was moistened and the wind had a southern component. On the other hand, the wind in the upper layer had a northern component. 3. The prediction of hail precipitation was better when an air mass of 900mb was used instead of 850mb in the method of Sowalter instability index. 4. The relations among the wind direction, the wind speed and the temperature depression which were found in the south of the radar echo clusters were different from that found in the east. 5. The hail precipitation and the peak of wind speed were observed after 30-40min of the change in wind direction. 6. The area of the maximum precipitation was apart from the area of the maximum temperature depression. It was considered from the trajectories of the temperature depression curves that the maximum temperature depression was due to multiple passages of thunderstorms.