Characteristics of atmospheric conditions, clouds and precipitation in a winter convective snowfall event over the Kanto Plain in Japan

Convective precipitation in the Kanto Plain of Japan during winter is not well understood due to limited detailed observations of atmospheric conditions, cloud and precipitation characteristics. This study analyzed a convective precipitation event on 26 January 2019, using surface meteorological observations, radar data, and measurements from a ground-based microwave radiometer and disdrometer at Tsukuba. The results revealed that convective clouds developed along a convergence line in the lower atmosphere, within a synoptic field characterized by an intensified winter monsoon. Stability indices derived from the microwave radiometer indicated increasing atmospheric instability prior to the precipitation event, which was attributed to increasing surface temperatures combined with the inflow of cold air into the upper atmosphere. During the event, two separate precipitation events were recorded at Tsukuba. A rapid increase in liquid water path was observed approximately 10 minutes before the first event. Disdrometer analysis revealed that graupel particles in the first event and graupel and small particles in the second were dominant, respectively. The average particle mass was also larger in the first event. Photographs of precipitation particles from citizen science showed that particles in the first event were more densely rimed compared to those in the second. These differences in precipitation characteristics are suggested to result from variations in the convective clouds, either isolated or organized. These findings could contribute to improved nowcasting of convective snowfall in the Kanto Plain during winter.