By using the objective similaritymethod, A short - range forecastmodel of hail in Gannan Plateau was comp leted. The system comp iled by four parts, including a history database of hail, similar case and judgment, viewing history weathermap and comparing with intraday actually happening, adding new hail data. The result shows that the model has a good effect in short - range forecast of hail, and it is an effective method of short - range forecast.

By using the data of eightweather stations’records of thunderstorms over Gannan p lateau from the beginning of each station’s establishment to 2005, the temporal and spatial distribution features of thunderstormswere analyzed. The results show that thunderstorm occurred more frequently inMaqu, Luqu and Hezuo counties; The annual thunderstorm days p resented descending trend and the trend ismore obvious after the middle of the 1990 s, but the variation of the duration days between the beginning and the ending time of thunderstorm occurring in Gannan p lateau is not very distinct; Summer is thunderstorm season and July is the month in which thundstorms occurmost frequently, and the percentage of thundstorm times in July is 20. 2%. The late sp ring and early summer, the third ten - day of June, the second and third ten - day of July, the third ten - day ofAugust are the peak periods for thunderstorms occurring in Gannan; The daily thunderstorm occurring peak time is 14: 00 - 15: 00, and the percentage of thundstorm times is 30. 3% in this period.

An abrup t severe storm occurred on August 30 - 31 of 2006 in the Gannan Plateau was analyzed. Results show that the combination of convective clouds from the southeast of Qinghai and the local convective cloud ismain cause resulting in this p rocess, and the severe storm and hail occurred on the front of right side of the convective cloud. The development of airflow leaning east at the height of 600 - 700 hPa over the eastern part of Gannan p lateau is very important to the severe storm’s occurring and develop ing. The distributions ofθse high energy center at 700 hPa level,θse departure between 500 hPa and 700 hPa, the helicity and vapor flux divergency fields at 700 hPa level are meaningful to estimate the occurring region of this severe storm.