Causes of Hail in West Sichuan Plateau in May

Causes of Hail Occurring in Western Sichuan Plateau in May;

Hail weather in Aba Prefecture mainly occurs from March to 10, with the most hail days in May. In terms of daily variation characteristics, hail is mainly concentrated in14 ~19; The spatial distribution of hail is mainly concentrated in the northwest area above 3000 meters above sea level. The severe hail weather situation in Aba Prefecture can be divided into three typical types: Tibet high pressure type, northwest airflow type and plateau shear type. In general, due to the unstable stratification and the influence of cold air on the ground, strong convective weather such as heavy hail is prone to occur. According to environmental parameters, 75. 8% cases reached the unstable state of dry upper and wet lower; More than 75% of the heavy hail occurred in unstable stratification with vertical temperature difference of 400～600 HPA above 65438 07℃, with 500hPa upward movement and negative BLI. The vertical wind shear corresponding to 400 ~ 600 hectopascals mostly exceeds 8.2 m s ~ (-1); CAPE values are mostly above 325 J kg- 1, and CIN values are mostly below 14.4J kg- 1. SSI values are mostly greater than 226. 4.