Analysis of Observational Characteristics of Extra-large Hail in Shandong Peninsula on 1 October 2021

Based on observational data, ERA5 hourly reanalysis data, and s-band dual-polarization radar data, the extremely severe convective weather happening in Shandong Peninsula on 1 October 2021 is analyzed. The results show that: The process was affected by the upper-level cold vortex, and extremely severe convective weather happened from west to east in the northern area of Shandong Peninsula. Extra-large hail occurred in this process. The upper-level cold vortex provided the synoptic-scale dynamic forcing and unstable thermal stratification conditions, which were conducive to the occurrence of severe convective weather. About 2400 J•kg^-1 sufficient CAPE and 30.2 m•s^-1 strong vertical wind shear between 0 and 6 km altitude prompted this severe convective weather to arise in October. Due to the special coastal geographical environment of Shandong Peninsula, the surface sea-breeze front triggered this severe convection process, and the movement of the surface convergence line stimulated the occurrence and development of convection nearby upstream and downstream. The mean values of the maximum reflectivity (DBZM), cells-vertical integrated liquid (C-VIL), the top height of the strong reflectivity center (HT) and the top height of the cell (TOP) of the supercell storm which lasting for about 3 h were 70.7 dBZ, 68.9 kg•m^-2, 3.2 km, and 11.4 km respectively. The three-body scatter spike (TBBS) and bounded weak echo region (BWER) of the storm were very significant. The value of Z_DR is lower below 0℃ layer than that above 0℃ layer，meanwhile the values of CC and K_DP is higher below 0℃ layer than that above 0℃ layer. There were two Z_DR columns on the east and west sides in the supercell storm and the height of east Z_DR column top exceeds that of the -20 °C layer. The thickness of the east Z_DR column (about 3.2 km) was thicker than that of west Z_DR column (about 2.2 km). These all indicate that the storm had a deep updraft, which was conducive to the formation and growth of hail. There were also two K_DP columns on the east and west sides of the BWER, which had almost the same thickness about 3.2 km, and both extended beyond the height of the -20°C layer. The thickness of the strong reflectivity above 65 dBZ reaches 7 km, and the thickness of the Z_DR column and K_DP column reaches 2-3 km can be used as a reference for predicting extra-large hail in autumn short-term forecasting.