Abstract:Severe rainstorms struck South China on 7 May 2018, which were related to front-driven mesoscale convective system (MCS) and quasi-stationary MCS in warm zone. South-moving frontal MCS led to wide range of un-uniform precipitation, and warm-sector MCSs with short life time induced multiple mesoscale rainbands within the range of 30-200 km south to surface front. Quasi-stationary line-type MCS along the coast of South China grew up to 300 km in length, sustained more than 12 h and induced extremely severe rainfall beyond 300 mm. All types of MCS showed the low-echo-centroid structure on the vertical section of reflectivity, and the averaged 35 dBz echo-top was at the height of 5.5 km for frontal MCS cells, compared with 4.7 km for convective cells in warm sector. Analysis of raindrop size distribution revealed that MCS in coastal zone was with larger raindrop diameter and higher nuclei concentration compared with frontal MCS. Averaged large-scale precipitation efficiency of frontal convective system was at about 10%-15% according to ERA5 reanalysis, while the precipitation efficiency of MCS in warm zone could increase instantaneously more than 90%. Operational numerical models showed limited predictivity for convective precipitation in warm zone, while EC-Reforecasts showed improved performance on ensemble spread for the convective precipitation near South China coast. Mesoscale model’s forecast showed basic patterns of frontal MCS and warm-sector MCS, however obvious bias existed in the organization and intensity of MCS along coastal zone. Ensemble sensitivity analysis indicated that frontal MCS showed high sensitivity to synoptic forcing related to low pressure trough and low-level jet intensity, while convection in warm sector showed high sensitivity to CAPE in upstream environment.