Abstract:By using the reflectivity, radial velocity,Vertically Integrating L iquid (V IL) Water Content and other p roducts of Chengde
Dopp ler radar, a squall line p rocess happened in Chengde on 25 June 2008 was analyzed combining circulation situation and automatic
weather station data. Itwas discussed how Dopp ler radar echoes of the squall line in Chengde evolved. The results show the strongwind
locates in bulge spot of the bow squall line echo. The negative center value of radial velocity increased gradually then more than 27 m /
s and app roached the radar,which indicated that the strong wind would occur. V IL value increasing rap idly, reducing sharp ly and the
continued high Echo Top s (ET) value have corresponding relationship swith the strong wind, hail and so on.

By using the theory ofmoist potential vorticity(MPV) , a rainstorm occurred in northeast of Hebei Province on 25 June 2008 was analyzed. The results show that the heavy rain occurred in the neighborhood of the stiff and dense section of Pseudo - equivalent potential temperature lines, where the convective stabilitywas so small that itwas beneficial to the development ofmoist baroclinic vorticity. The overlapp ing of the positive and negativeMPV1 areas at the lower and upper levelwas advantageous to the development and appearance of rainstorm, and the rainstorm was located near the zero line ofMPV1. MPV1 < 0 andMPV2 > 0 at the level of 850 hPa can be a useful condition for rainstorm occurring in the north of Hebei Province.

Based on the conventional data, satellite cloud images and Dopp ler Radar data, the snow storm weather occurred in sp ring of
2007 in Chengde was analyzed from the large - scale background, water vapor and dynamic conditions. The results indicate that the
block from the eastern p ressure ridge leads to themerger and intensification of the north and the south low - p ressure systems, andmov2
ing slowly of the low - p ressure system results in this storm event. The convergence in the lower level and the foundation of low level jet
made large - scale water vapor convergence and continualwater vapor transmission, and the deep - thick atmosphere wet layer p rovides
a favourable surrounding condition and the divergence, vertical velocity and k - helicity fields are dynamic conditions for this heavy rain.