For the purpose of the clarification of meso-scale winter snow storms, Nagoya University installed dual Doppler Radar system on the coast of the Sea of Japan during the period from December 2002 to February 2003. On January 29th 2003, the strong cold air moved over the northern Japan and active snow clouds were observed over the Sea of Japan. On this day, during the period from 1800JST to 2000JST, dual Doppler Radar system observed selectively developed snowband, whose echo top height was exceed 5 km. The upper layer cold air was leaving away from the Hokuriku district, influence of geographical feature and land-breeze were not found. This snowband occurred at a distance from band-like cloud associated with the Japan Sea Polar-airmass Convergence Zone (JPCZ), it was suggested the snowband was differ from the disturbance occurred along the JPCZ. Moreover, the snowband developed in situation that band-like cloud associated with JPCZ was decaying. To reveal the structure and formation process of those kind of developed snowband, we investigated dual Doppler Radar data and numerical simulation model.

From the Doppler Radar observation, this snowband was composed of number of convective cells. These convective cells are occurred both in upstream and downstream of the snowband, lined up along predominant wind direction and organized linear structure. In lower layer, west-northwesterly wind was observed in north side of the snowband, while westerly wind was observed in south side of the snowband. Therefore, clear convergence line was formed along the snowband in lower layer. In particular, downstream region of the snowband northwesterly inflow from a long distance was observed, low level convergence was intensified locally there. It is suggested that an enhancement of low level convergence played an important role in maintenance of the linear structure of the snowband and occurrence of convective cells in downstream region of the snowband.

In result of numerical experiments, when the snowfall system associated with JPCZ was began to decaying, the snowband was formed on south side of JPCZ. At low the level, the cold air was present in southern edge of the snowband, and high equivalent potential temperature air was inflowing from north side of the snowband. Owing to convergence of these airmass high equivalent potential temperature airmass was lifted up, and formed convective cells. As a result, the snowband was developed on south side of JPCZ. Furthermore, it is important to reach high equivalent potential temperature airmass to the south of JPCZ, the snowfall system associated with JPCZ should be in the decaying stage because the upper layer cold-air was moving away from over the Sea of Japan and the stability of atmosphere was increasing.