Abstract
　Winter thunderstorms have often occurred in Ishikawa prefecture. In this report, a case of the cloud-to-ground discharge on December l986 is analyzed according to the data of“The Thunderstrm Detection Systems” in the Komatsu air base near the cloud-to-ground discharge point.
　The followings were concluded;
1) The cloud-to-ground discharge occurred in the area of surface positive strong electric field. (over 20 kV/m)
2) And this discharge point was located in the leading edge of the strong radar echo.(over 50 dBZ)
3) By using the data of field mills and weather radar, we can forecast hazards of cloud-to-ground discharges befor about half an hour.

【キーワード】：落雷, レーダーエコー, 雷電探知システム

*防衛大学校地学教室
Inst. of Ceosciences ＆ Astronomy, The National Defense Academy