Based on the mathematical forecast product“T639”and snowfall data in the middle part of the north slope of Tian Mountain，this paper analyzed the synoptic character and causes of the torrential snowfall weather ocurred there on February 23 of 2010．Results show that Ural ridge and Siberian cold vortex moving to eastward provided large scale circumfluent background for this snowfall weather，and the mesoscale short wave，southwest jet stream，700 hPa mesoscale convergence belt，850 hPa shear line，middle－high pressure，middle－low pressure and ground cold front were direct influence systems of this snowfall weather．The high－low level situation field，jet stream and front regions，and the favorable cooperation of middle scale momentum and water vapor，these all provided necessary conditions for this torrential snowfall weather．The high－level jet stream increased vertical movement，the strong low－level southwest warm and humid jet stream transported instable air flow with high temperature and humidity from the Caspian Sea and Black Sea to the middle level of Tian Mountain north slope，which provided heat，water vapor and unstable energy conditions for this orrential snowfall weather．

The paper analyzed a hailstone weather occurred in the Zhunger south edge’s region on June 28，2010 based on the routine
data，automatic meteorological station data and CINRAD/CC Doppler radar data．The results showed that the heavy convection weather
occurred under the condition of high altitude trough cooperated with ground cold front and instable atmospheric stratification，dry and cold in middle－high layer and warm and wet in low layer，abundant water vapor，fitting height of 0℃layer and－2．0℃layer，meanwhile there was heavy vertical wind shear．Doppler radar reflectivity factor PPI appeared＞50 dBZ heavy echo section and＞60dBZ heavy echo center．The RHI appeared cove configuration，and the height of＞50 dBZ echo section was more higher than that of 0 ℃layer．The radial velocity map showed mesocyclone，against the wind section．It presented low layer convergence and high layer divergence in hailstone area．Updraft in PPI of different elevations showed circumrotating and rising．Strong echo section corresponded well to against the wind section and mesocyclone，meanwhile VIL，mesocyclone and storm track information products had good indication for hailstone drop．