A wind gust of F0 scale occurred in Shonai town, Yamagata Prefecture, Japan, on 4 December 2015. It damaged some houses in a narrow valley 24 km from the coast of the Japan Sea. Around that time, one of many isolated convective clouds greater than 6 km in height traveled over the area. Observation of two Doppler radars with high resolution in time and space showed that a cyclonic vortex generated at the south edge of the convective cloud after landfall from the Japan Sea rapidly developed with increasing vorticity as it moved inland. The vortex traveled across a mountain, and its southern part near its center subsequently passed over the damaged area. The radius and vorticity of the vortex were 0.64 km (misoscale) and 0.048 s?1, respectively. A hook-shaped echo, a vault-shaped echo, and a couplet of maximum and minimum Doppler velocities, which indicate the existence of a vertically oriented vortex tube, are clearly shown. This study discusses the development of the winter misocyclone observed by the radars in terms of the relationship with the behavior of the parent cloud and the possible topographical influence of the mountain and valley on the vortex structure.
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