Abstract:The weather process of the snowstorm happened in Hami Xinjiang during 1 8—20 November 2005 and the snow was heavier in the south than that in the north. Based o n NCEP 1°×1° 6h interval reanalyzed data and the non conventional data, dyna mic and thermodynamic diagnoses of the snowstorm caused by the vortex are discuss ed. And the methods of the Q vector and the helicity are also used to the fu rther analysis. The results are as follows: (1) With the development and eastward mo vement of the ridge in the west of Xinjiang, the vortex in Sayangling moved into Hami area and caused the snowstorm. (2) This Sayanling vortex was a deep er and cyclonic system with upward motion. There was a convergence in the low leve ls and a divergence in the high levels. (3) The obvious temperature advection an d temperature gradient can be revealed, so the baroclinicity was favorable to th e intensification and development of the vortex. (4) The convergence area of the Q vector and the positive helicity area were consistent with the vortex, wh ich can be used as an indicator in forecasting the snow in Hami.