Abstract: In this paper,the variation characteristics of hail stone in the range of May to August from 2005 to 2014 were analyzed by using the observation records of meteorological stations on the north side of Tianshan Mountains,the records of artificial hailings,Karamay sounding data and detection data of four radars. The radar echo characteristics and the moving path of the hail cloud were studied and forecast index and radar warning index of the hail cloud are determined based on the percentile method. Moreover,the forecast and forecasting indexes were validated by the hail record data and radar detection data in the rage of 2015 to 2016. The results showed as follows: (1)Hail stone appeared on the north side of the Tianshan Mountains in the past 10 years,focused on the period from May to August and most appear in July,especially at 16:00-22:00 PM and most at 19:00 PM. (2)Echo tops (ET)of 7.0-13.0 km (average 10.34 km),40 dBz echo depth (ED)of 4.88-11.40 km (average 8.42 km),45 dBz echo depth (ED)of 3.86-10.65 km (average 7.44 km),50 dBz echo depth (ED)of 2.90-9.51 km (average 6.55 km). Maximum echo intensity of 51.4-65.8 dBz (average 57 dBz),combined reflectivity of 49-62 dBz (average 54.5 dBz)and vertical accumulation of liquid water content of 3.2-35.3 kg·m^-2 (average 16.7 kg·m^-2)are the radar characteristics for hail stone disaster from May to August. (3)Hail stone in the north of the Tianshan Mountains was formed in the Torrey Mountains (the west of Karamay City)and the Aiding Lake Valley (west of Wusu County). The three migration paths of hail cloud were northwest,northwest and west,southwest and west. (4)The potential forecasting index of hail cloud in the range of May to August is 0 ℃ layer height difference smaller than 3 872 m,freezing layer thickness is less than 3 236 m,K index is bigger than 23 ℃ and SI index is smaller than 3.85. (5)The Radar warning indexes of hail cloud in the range of May- August before hail 30 min are: the echo top height is bigger than 7.0 km,0 ℃ layer height difference bigger than 3.47 km. 40,45,50 dBz echo height is respectively greater than 4.96 km,4.38 km,4.18 km and the 0 ℃ layer height difference is bigger than 1.75 km,1.06 km,0.69 km. Moreover,the combined reflectance is greater than 42.9 dBz,vertical cumulative liquid water content is greater than 3.1 kg·m^-2. The Radar warning indexes of hail cloud in the range of May-August before hail 15 min are: the echo top height is bigger than 8.0 km,and the 0 ℃ height difference is bigger than 4.81 km. 40,45,50 dBz echo height is respectively greater than 5.99 km,5.10 km, 4.80 km and the 0 ℃ layer height difference is bigger than 2.78 km,2.03 km,1.14 km. In addition,combined reflectivity bigger than 47.5 dBz,vertical cumulative liquid water content bigger than 4.54 kg·m^-2,thickness of upwind zone in the radial wind field is exceeds 3km and existing wind cyclonic convergence in velocity field. The validation test of the forecast indexes and the radar warning indexes of the hail cloud in the rage of 2015 to 2016 shows that these indexed can play decisive role for forecast and early warning.

Key words: echo tops(ET), vert integrated liquid(VIL), composite reflectance(CR), moving path, nowcasting indicators