Extended Abstract

abFig.1 (a) Total precipitation (mm) from 08:00 BST on 18 July to 8:00 BST on 19 July, 2007; and (b) totalprecipitation (mm) from 17:00 BST to 20:00 BST on July 18, 2007 at Jinan automatic weather stations(the shadedareas indicate the Jinan urban area).2. DataThe data include the conventional observations, FY-2 satellite infrared and visiblecloud images, and the meso-scale automatic weather station data.3. Background before the PECS formationThe east Asian trough presented near the mid-latitudes of Japan at 200 hPa, andless moved (Fig. 2a). A long wave trough situated from inner Mongolia to Xinjiangprovince. Between the two troughs was the power South Asia high. The upper-levelwesterly jet was located in the north of the South Asia high, and the maximum windsexceeded 48m/s , with obvious anti-cyclonic curvature( Fig.2a).Figure 2b gives theGeopotential height, temperature and wind fields at 850hPa. Obviously, the maximumwind speed of low-level jet that over 18m/s existed in south China. On the left of thelow level jet was Shangdong province. From figure 2c, the lower southwest flow in thenorthwest side of subtropical high transported vapor to north China continuously. Atthis time, Jinan city was the center of strongest water vapor flux convergence zone.This weather situation caused a wide range of wet unstable energy region(θse500-θse850