利用常规观测资料对2008年7月18—19日山东潍坊出现的大暴雨天气过程进行诊断分析，结果表明，由于副高和贝加尔湖阻高的强大稳定，西风槽不断引导弱冷空气向东南方向移动，与沿台风北上的暖湿气流交汇，使位于副高西侧的潍坊地区发生强降水。此次强降水过程出现在低空辐合、高空辐散的上升运动区中，辐合层比较深厚。925hPa层是一关键层，不但提供充沛的水汽，而且该层较强的水汽辐合为大暴雨的产生提供了充足的水汽供应。正涡度中心区集中的时段，与强降水最集中时段相对应。大暴雨出现在相当位温陡峭密集区内的略偏北一侧。此次强降水是在对流层低层强对流不稳定（MPV1<0）的条件下发生的。降水落区与低层正MPV2分布相一致，低层MPV2的分布对暴雨落区的预报有较好的指示意义。

Based on the routine observational data, a diagnostic analysis is performed of the severe storm on 18—19 July 2008 in Weifang, Shandong Province. It is shown that the heavy storm is caused by the interaction between a weak cool front in the westerlies and the warm and wet air along the path of typhoon owing to the powerfulness and stability of the subtropical high and atmospheric blocking in Baikal. The southeast warm and wet air along the path of typhoon is the main vapour source of the rainstorm. The heavy rain occurs in the powerful updraft condition with convergence at low level and divergence at high level. The convergence layer is thick, which is the cause of heavy rain. The 925hPa layer is an important layer with respect to the event because of its role in supplying plentiful vapour. Concentrated period of time of positive vorticity center corresponds to the period of heavy rain, which is propitious to the development of convection. It occurred in the north of the very stiff and dense section of moist isentropes and in the low troposphere of strong convective instability (MPV1<0). The region of positive MPV2 at low level has a very good correlation with the location of rainstorm. The distribution of MPV2 at low level may provide a good indicator for the forecast of rainstorm region.