A Mie scattering laser radar with a powerful flashlamp-pumped dye laser has been developed to measure “Yamase” fog which is caused by very cold air intrusion as a result of Okhotsk high pressure. The inner structure of the “Yamase” fog—height profile, horizontal distribution, speed, thickness of the fog layer and its time development, periodic movement and dominant periods were observed and analyzed for the first time by laser radar of our institute.