The development of slantwise vorticity near a weakened tropical .
减弱热带气旋附近的倾斜涡度发展。
The combined action of surface front , mesoscale convergence line and sub synoptic scale cold vortex accompanied with positive vorticity advection resulted in rising airflow which made thunderstorm produce first in south central shanxi . The thunderstorm moved towards southeast from the taihang mountain to henan and developed vigorously in the advantageous environment .