An infrequent continuous rain weather process occurred from September 25 to October 14 in 2007 in northwestChina was studied from theweather and climate background, upper and lower level circulation, surface situation and some physical factors. The results show that frequent activity of thewesterly trough and anomaly of the subtropic high pressure location resulted in this infrequent continuous autumn rain. Moreover, the position ofSouthAsia high at the levelof100 hPa, 500 hPawind field and the position of zero line has some significance for rainfall prediction.

A severe convective storm process occured in the middle of Gansu province on May 30，2005 was analyzed by using CIN·RAD／CC Doppler weather radar data．It is found that the main meso—scale system causing this 8evere convective storm was the squall hne．The storln first appeared at 15：00，then moved to the southeast，and from 16：15 to 17：03 the multi—cell storm became more strongly and developed into the super—cel storm with the characteristics of vortex and zonal echoes．Th ere were two obvious outflow boundaries observed in south of the supercel lying to the southwest and southeast of the hook echo of the storm ，respectively．The shape of the low elevation reflectivity in the left front flank of the superceU was an inverted“V”，the maximum of echo intensity ap-poared in the bounded weak echo zone with the value over 70 dBZ．Th e corresponding radial velocity maps showed a strong mature me·so—cyclone feature．In this period the maximum vertical integrated liquid water(VIL)reached above 70 ks／m and the height of echo top(ET)was 17—18 km．Hence，this storm presented the typical features of superceU storms．

Using the daily snowfall，temperature data during1995~2000（in November，December，January，February）and 500，700 hPa circulation situation pictures of high altitude and ground in 1990~2000（in November，December，January，February），thepaper analyzed the temperature，precipitation variation tendency and 24 snowfall examples in winter of the past 50 years，demonstrated the weather situation background for snowfall and its occurring，developing as well，and set up the clearer forecast mentality，forecast model and forecast examples to rehouse