This study conducted synoptic and mesoscale analyses to understand the cause of Japan Tsukuba tornado development, which occurred at 0340 UTC 6 May 2012. Prior to the tornado occurrence, there was a circular jet stream over Japan, and the surface was moist due to overnight precipitation. The circular jet stream brought cold and dry air to the upper-level atmosphere which let strong solar radiation heat the ground with clearing of sky cover. A tornadic supercell developed in the area of potentially unstable atmosphere. Sounding data at Tateno showed a capping inversion at 900 hPa at 0000 UTC 6 May. Strong insolation in early morning hours and removal of the inversion instigated vigorous updraft with rotation due to vertical shear in the upper-level atmosphere. This caused multiple tornadoes to occur from 0220 to 0340 UTC 6 May 2012. When comparing Tateno’s climatological temperature and dew-point temperature profile on the day of event, the mid-level atmosphere was moister than typical sounding in the region. This study showed that tornado development in Tsukuba was caused by a combination of (a) topography and potential vorticity anomaly, which increased vorticity over the Kanto Plain; (b) vertical shear, which produced horizontal vortex line; and c) thermal instability, which triggered supercell and tilted the vortex line in the vertical.

Abstract
 Introduction
 Data and Analysis Method
  Analysis data
  Analysis method
 Analysis Results
  Synoptic analysis
  Moisture and thermodynamic analyses
  Dynamic analysis
 Summary and Conclusions
 References

• Seonhee Choo(Forecast Technology Division, Forecast Bureau, Korea Meteorological Administration)
• Ki-Hong Min(Major in Atmospheric Sciences, School of Earth System Sciences, Kyungpook National University) Corresponding author
• Kyung-Eak Kim(Applied Meteorology Research Division, National Institute of Meteorological Sciences)
• Gyuwon Lee(Major in Atmospheric Sciences, School of Earth System Sciences, Kyungpook National University)