Based on the numerical prediction interpretation techniques and forecast experiences，the short － term objective forecast system
of meteorological elements for Northwest China is established． With the aid of meteorological data of real － time observation，the
verification and assessments of objective forecast from the system － output for air temperature and precipitation in winter of 2006 have
been performed． The results show: ( 1) The forecast accuracy of maximum and minimum temperature is much higher than that of precipitation
with the accurate rates of 70% and 34%，respectively． ( 2) The factors affecting the forecast accuracies of temperature and
precipitation are the static stability of atmosphere and relative humidity． ( 3) If the system established on month scale，the forecast accuracy
of temperature is expected to have a 10% improvement．

Based on the reflectivity factor of CINRAD ( the constant altitude p lan data) interpolated with 3D - Barnes scheme assuming that the reflectivity factor of solid water drop would accord with the experiential relation of the reflectivity factor induced by the liquid water drop, Vertically IntegratedWater Content (V IWC) including solid and liquid water was calculated with the method of discrete sum instead of vertical integral. The ratio ofV IWC and the up right height of hail cloud is defined asVertically IntegratedWater Content Density(V IWCD) , the maximum V IWCD ( shortened form: V IWCDmax) is identified by use ofMAX function. With methods of statistic and regression equation, the correlation between the V IWCDmax of hail cloud during hailing p rocess and the maximum hail diameter on the ground is analyzed in detail for 54 hail clouds observed by Lanzhou CINRAD during 2004 - 2006. Results show that the magnitude about number density of hail pellet coming from hail embryo in hail clouds with the same maximum diameter is equivalent during hailing p rocess, and hail pellet scale is an important factor which determined hail cloud echo intensity and hail size on the
ground; the p iecewise function (6) which is affected by two important factors of hail cloud tilted structure and radar scanmodel reflects the correlation between the V IWCDmax of hail cloud during hailing p rocess and the maximum hail diameter.