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 basic observationaldata and automaticweather station data, a regionalheavy dust storm occurred onApril29,2009 inHexiCorridorwas analyzed from the causes of the synopticmeteorology, physics quantity fields and so on.The results show that itwas a duststorm thatcaused by the gale behind the cold front, and ithappened in the zone ofstrong pressure gradient. Groundmeteorological elements had a strong response to the outbreak of the dust storm, which can be used as a reference for forecast of dust storms. Therewas an obvious upwardmotion in the outbreak area ofduststorm with the lower level convergence and the high-leveldivergence. The frontogenesis function and helicity indicated the area of dust storm verywel.l
The app lication of K drought index for droughtmonitor operation in Gansu was introduced in this paper, and the mainly analysiswas as follows: the definition, grades, criterion, app lication of K drought index, and the comparison between monitor results of K drought index and actual drought situation. Results indicate that there is a good effect in droughtmonitorwith K index compared to actual drought situation in sp ring, May, June, July to August, and Sep tember in 2008 in Gansu p rovince.
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.
A preliminary analysis on the first regional hail process which occurred on May 14 to 15 in 2004 was given,including its atmospheric circulation,the background of previous climate and the field of physical quantities,and the conditions under which this type of weather process occurs was established .This has certain instructing meaning to forcast such process accurately within short and medium terms.
