Abstract:The features and formation of a severe convection process are studied by using the conventional observation data, automatic weather station data, GFS analysis field data with special resolution of 0.5° and temporal resolution of 6 h, Doppler radar, radar wind profiler and microwave radiometer data collected in Zhejiang Province on 26 July 2014. The results suggest that the severe convection process near the edge of subtropical high was due to the penetration of cold air caused by the east movement of the upper trough and accumulation of unstable energy, as well as the ambient background of dry and cold in upper layer but wet and warm in low layer, such unstable stratification condition and background was favorable for occurrence of the severe convection. Good predictability was provided when low level 925 hPa mesoscale convergence line overlaid the vertical upward region in the middle of troposphere at 700 hPa. This means that severe convection could happen near the mesoscale convergence line in next 6 h under such situation. The Ningbo mesoscale convergence line, which was produced by confluence of southerly flow and northeasterly flow, triggered the severe convection in Ningbo. What’s more, the convergence line already existed under the orographic influence of coastal line and Hangzhou Bay. In contrast, the Hangzhou mesoscale convergence line, resulting from the convergence of ambient northeasterly current and easterly airflow enhanced by surface outflow of Ningbo thunderstorm, gave rise to the outbreak of the severe convection around Hangzhou.