Abstract:Extreme rainstorms struck Henan Province during 17 to 22 July 2021. With the enhancing of the upper tropospheric cold low (UTCL) over the China East Sea, the precipitation in Henan burst almost simultaneously, indicating that UTCL has potential impact on the development of the precipitation. From 19 to 22 July, the upper-level short-wave trough over Hetao Area, the high ridge over Huanghuai Region, UTCL and the blocking high over Japan Sea formed a wave train which led to the almost stationary synoptic circulations. During the heavy rainfall, UTCL stagnated over the eastern seas of China, resulting in large-scale divergence in westerly jet over Henan Provice and its eastern region. The establishment and enhancement of the upper-level divergence over Henan was clearly related to the acceleration of northwest jet on the west part of UTCL. Meanwhile, south flow jet on the eastside of UTCL enhanced the upper-level outflows of Typhoon In-fa, which was conducive to the growth of In-fa’s circulation and the water vapor transportation to the rainstorm area of Henan. On the other hand, the upper-level sinking caused by UTCL enhanced the stability of the subtropical high, and also enhanced the low-level water vapor transportation from the East China Sea to Henan. The UTCL showed obvious forecast uncertainty. From adjacent forecast cycles, the center of UTCL continued to adjust to the north, intensifying and the heavy rainfall area in Henan also tended to adjust to the east direction. The comparison between strong and weak UTCL circulation among ensemble members shows that, strong UTCL circulation was conducive to enhance the anticyclonic divergent outflow over Henan and was more conducive to the enhancement of precipitation in Henan, which has been also proved by ensemble sensitivity analysis.