Causes of heavy rains in northwest China

The heavy rain process is a southwest airflow type on the northwest side of a subtropical high in the eastern part of the northwest region. This heavy rain is a strong convective precipitation caused by medium-α and medium-β scale convective clouds. The clouds over the Tibetan Plateau are renewed after they move to northwest Sichuan, and new clouds are formed in front of the old clouds when they die. After the cold front cloud belt reaches the Hedong area of ??Gansu Province, its front edge also triggers convective cloud clusters. Affected by the strong water vapor transport belt in the Sichuan Basin, new cloud clusters are generally generated on the left side of the water vapor transport belt. Heavy rain areas occur when cold front cloud belts combine with convective clouds. The development of convective clouds is the result of the combined effects of water vapor transport and weather system convergence, as well as favorable local environmental conditions such as double-layer convective instability and topography. . Regional heavy rain occurs in the overlapping area of ??cold front cloud belts and convective clouds, where precipitation efficiency is high. Most of the heavy rain areas are located in the northwest or northeast of the convective clouds and the cold front cloud belt.

Time: I remember once in March 1999 and once in June 2003.