Numerical Simulation of a Case of Heavy Rainfall in the Northern Tohoku Region of Japan on 9 August 2013

Two quasi-stationary quasi-linear convective systems caused local heavy rainfall on 9 August 2013 in the northern Tohoku region of Japan. We investigate this rare event in the region using a numerical simulation and examine airflow structures and mechanisms. The amount and locations of the simulated precipitation agree well with the observed values. The environment is favorable to convective systems, and analyses based on forward trajectories and composites of convective cells clarify airflow structures. Mountains upstream of the extreme precipitation areas trigger the back-building convective systems, whereas humid low-level inflows converging below the convective systems play a role in maintaining the convective systems downstream where there are no significant mountains.